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Musmaker K, Wells J, Tsai MC, Comeron JM, Malkova A. Alternative Lengthening of Telomeres in Yeast: Old Questions and New Approaches. Biomolecules 2024; 14:113. [PMID: 38254712 PMCID: PMC10813009 DOI: 10.3390/biom14010113] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2023] [Revised: 01/11/2024] [Accepted: 01/12/2024] [Indexed: 01/24/2024] Open
Abstract
Alternative lengthening of telomeres (ALT) is a homologous recombination-based pathway utilized by 10-15% of cancer cells that allows cells to maintain their telomeres in the absence of telomerase. This pathway was originally discovered in the yeast Saccharomyces cerevisiae and, for decades, yeast has served as a robust model to study ALT. Using yeast as a model, two types of ALT (RAD51-dependent and RAD51-independent) have been described. Studies in yeast have provided the phenotypic characterization of ALT survivors, descriptions of the proteins involved, and implicated break-induced replication (BIR) as the mechanism responsible for ALT. Nevertheless, many questions have remained, and answering them has required the development of new quantitative methods. In this review we discuss the historic aspects of the ALT investigation in yeast as well as new approaches to investigating ALT, including ultra-long sequencing, computational modeling, and the use of population genetics. We discuss how employing new methods contributes to our current understanding of the ALT mechanism and how they may expand our understanding of ALT in the future.
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Affiliation(s)
- Kendra Musmaker
- Department of Biology, University of Iowa, Iowa City, IA 52242, USA (J.W.)
| | - Jacob Wells
- Department of Biology, University of Iowa, Iowa City, IA 52242, USA (J.W.)
| | - Meng-Chia Tsai
- Department of Biology, University of Iowa, Iowa City, IA 52242, USA (J.W.)
| | - Josep M. Comeron
- Department of Biology, University of Iowa, Iowa City, IA 52242, USA (J.W.)
- Interdisciplinary Graduate Program in Genetics, University of Iowa, Iowa City, IA 52242, USA
| | - Anna Malkova
- Department of Biology, University of Iowa, Iowa City, IA 52242, USA (J.W.)
- Interdisciplinary Graduate Program in Genetics, University of Iowa, Iowa City, IA 52242, USA
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2
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D’Angiolo M, Yue JX, De Chiara M, Barré BP, Giraud Panis MJ, Gilson E, Liti G. Telomeres are shorter in wild Saccharomyces cerevisiae isolates than in domesticated ones. Genetics 2023; 223:iyac186. [PMID: 36563016 PMCID: PMC9991508 DOI: 10.1093/genetics/iyac186] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2022] [Revised: 11/02/2022] [Accepted: 12/03/2022] [Indexed: 12/24/2022] Open
Abstract
Telomeres are ribonucleoproteins that cap chromosome-ends and their DNA length is controlled by counteracting elongation and shortening processes. The budding yeast Saccharomyces cerevisiae has been a leading model to study telomere DNA length control and dynamics. Its telomeric DNA is maintained at a length that slightly varies between laboratory strains, but little is known about its variation at the species level. The recent publication of the genomes of over 1,000 S. cerevisiae strains enabled us to explore telomere DNA length variation at an unprecedented scale. Here, we developed a bioinformatic pipeline (YeaISTY) to estimate telomere DNA length from whole-genome sequences and applied it to the sequenced S. cerevisiae collection. Our results revealed broad natural telomere DNA length variation among the isolates. Notably, telomere DNA length is shorter in those derived from wild rather than domesticated environments. Moreover, telomere DNA length variation is associated with mitochondrial metabolism, and this association is driven by wild strains. Overall, these findings reveal broad variation in budding yeast's telomere DNA length regulation, which might be shaped by its different ecological life-styles.
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Affiliation(s)
- Melania D’Angiolo
- Institute for Research on Cancer and Aging (IRCAN), Université Côte d’Azur, 28 Avenue de Valombrose, 06107 Nice, France
| | - Jia-Xing Yue
- Institute for Research on Cancer and Aging (IRCAN), Université Côte d’Azur, 28 Avenue de Valombrose, 06107 Nice, France
- State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Guangdong Key Laboratory of Nasopharyngeal Carcinoma Diagnosis and Therapy, Sun Yat-sen University Cancer Center (SYSUCC), 651 Dongfeng Road East, China
| | - Matteo De Chiara
- Institute for Research on Cancer and Aging (IRCAN), Université Côte d’Azur, 28 Avenue de Valombrose, 06107 Nice, France
| | - Benjamin P Barré
- Institute for Research on Cancer and Aging (IRCAN), Université Côte d’Azur, 28 Avenue de Valombrose, 06107 Nice, France
| | - Marie-Josèphe Giraud Panis
- Institute for Research on Cancer and Aging (IRCAN), Université Côte d’Azur, 28 Avenue de Valombrose, 06107 Nice, France
| | - Eric Gilson
- Institute for Research on Cancer and Aging (IRCAN), Université Côte d’Azur, 28 Avenue de Valombrose, 06107 Nice, France
- Department of Genetics, CHU, 06107 Nice, France
| | - Gianni Liti
- Institute for Research on Cancer and Aging (IRCAN), Université Côte d’Azur, 28 Avenue de Valombrose, 06107 Nice, France
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3
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Misino S, Busch A, Wagner CB, Bento F, Luke B. TERRA increases at short telomeres in yeast survivors and regulates survivor associated senescence (SAS). Nucleic Acids Res 2022; 50:12829-12843. [PMID: 36513120 PMCID: PMC9825167 DOI: 10.1093/nar/gkac1125] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2022] [Revised: 10/25/2022] [Accepted: 11/08/2022] [Indexed: 12/15/2022] Open
Abstract
Cancer cells achieve immortality by employing either homology-directed repair (HDR) or the telomerase enzyme to maintain telomeres. ALT (alternative lengthening of telomeres) refers to the subset of cancer cells that employ HDR. Many ALT features are conserved from yeast to human cells, with the yeast equivalent being referred to as survivors. The non-coding RNA TERRA, and its ability to form RNA-DNA hybrids, has been implicated in ALT/survivor maintenance by promoting HDR. It is not understood which telomeres in ALT/survivors engage in HDR, nor is it clear which telomeres upregulate TERRA. Using yeast survivors as a model for ALT, we demonstrate that HDR only occurs at telomeres when they become critically short. Moreover, TERRA levels steadily increase as telomeres shorten and decrease again following HDR-mediated recombination. We observe that survivors undergo cycles of senescence, in a similar manner to non-survivors following telomerase loss, which we refer to as survivor associated senescence (SAS). Similar to 'normal' senescence, we report that RNA-DNA hybrids slow the rate of SAS, likely through the elongation of critically short telomeres, however decreasing the rate of telomere shortening may contribute to this effect. In summary, TERRA RNA-DNA hybrids regulate telomere dysfunction-induced senescence before and after survivor formation.
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Affiliation(s)
| | - Anke Busch
- Institute of Molecular Biology (IMB), Mainz, Germany
| | | | - Fabio Bento
- Institute of Developmental Biology and Neurobiology (IDN), Johannes Gutenberg-Universität, Mainz, Germany
| | - Brian Luke
- Institute of Molecular Biology (IMB), Mainz, Germany.,Institute of Developmental Biology and Neurobiology (IDN), Johannes Gutenberg-Universität, Mainz, Germany
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4
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Malyavko AN, Petrova OA, Zvereva MI, Polshakov VI, Dontsova OA. Telomere length regulation by Rif1 protein from Hansenula polymorpha. eLife 2022; 11:75010. [PMID: 35129114 PMCID: PMC8820739 DOI: 10.7554/elife.75010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2021] [Accepted: 01/14/2022] [Indexed: 11/17/2022] Open
Abstract
Rif1 is a large multifaceted protein involved in various processes of DNA metabolism – from telomere length regulation and replication to double-strand break repair. The mechanistic details of its action, however, are often poorly understood. Here, we report functional characterization of the Rif1 homologue from methylotrophic thermotolerant budding yeast Hansenula polymorpha DL-1. We show that, similar to other yeast species, H. polymorpha Rif1 suppresses telomerase-dependent telomere elongation. We uncover two novel modes of Rif1 recruitment at H. polymorpha telomeres: via direct DNA binding and through the association with the Ku heterodimer. Both of these modes (at least partially) require the intrinsically disordered N-terminal extension – a region of the protein present exclusively in yeast species. We also demonstrate that Rif1 binds Stn1 and promotes its accumulation at telomeres in H. polymorpha.
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Affiliation(s)
- Alexander N Malyavko
- Faculty of Chemistry and Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, Russian Federation
| | - Olga A Petrova
- Faculty of Chemistry and Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, Russian Federation
| | - Maria I Zvereva
- Faculty of Chemistry and Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, Russian Federation
| | - Vladimir I Polshakov
- Center for Magnetic Tomography and Spectroscopy, Faculty of Fundamental Medicine, Lomonosov Moscow State University, Moscow, Russian Federation
| | - Olga A Dontsova
- Faculty of Chemistry and Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, Russian Federation.,Center of Life Sciences, Skolkovo Institute of Science and Technology, Moscow, Russian Federation.,Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry of the Russian Academy of Sciences, Moscow, Russian Federation
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5
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Sholes SL, Karimian K, Gershman A, Kelly TJ, Timp W, Greider CW. Chromosome-specific telomere lengths and the minimal functional telomere revealed by nanopore sequencing. Genome Res 2021; 32:616-628. [PMID: 34702734 PMCID: PMC8997346 DOI: 10.1101/gr.275868.121] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2021] [Accepted: 10/20/2021] [Indexed: 11/26/2022]
Abstract
We developed a method to tag telomeres and measure telomere length by nanopore sequencing in the yeast S. cerevisiae. Nanopore allows long-read sequencing through the telomere, through the subtelomere, and into unique chromosomal sequence, enabling assignment of telomere length to a specific chromosome end. We observed chromosome end–specific telomere lengths that were stable over 120 cell divisions. These stable chromosome-specific telomere lengths may be explained by slow clonal variation or may represent a new biological mechanism that maintains equilibrium unique to each chromosome end. We examined the role of RIF1 and TEL1 in telomere length regulation and found that TEL1 is epistatic to RIF1 at most telomeres, consistent with the literature. However, at telomeres that lack subtelomeric Y′ sequences, tel1Δ rif1Δ double mutants had a very small, but significant, increase in telomere length compared with the tel1Δ single mutant, suggesting an influence of Y′ elements on telomere length regulation. We sequenced telomeres in a telomerase-null mutant (est2Δ) and found the minimal telomere length to be ∼75 bp. In these est2Δ mutants, there were apparent telomere recombination events at individual telomeres before the generation of survivors, and these events were significantly reduced in est2Δ rad52Δ double mutants. The rate of telomere shortening in the absence of telomerase was similar across all chromosome ends at ∼5 bp per generation. This new method gives quantitative, high-resolution telomere length measurement at each individual chromosome end and suggests possible new biological mechanisms regulating telomere length.
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6
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The Power of Stress: The Telo-Hormesis Hypothesis. Cells 2021; 10:cells10051156. [PMID: 34064566 PMCID: PMC8151059 DOI: 10.3390/cells10051156] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2021] [Revised: 04/29/2021] [Accepted: 05/06/2021] [Indexed: 02/06/2023] Open
Abstract
Adaptative response to stress is a strategy conserved across evolution to promote survival. In this context, the groundbreaking findings of Miroslav Radman on the adaptative value of changing mutation rates opened new avenues in our understanding of stress response. Inspired by this work, we explore here the putative beneficial effects of changing the ends of eukaryotic chromosomes, the telomeres, in response to stress. We first summarize basic principles in telomere biology and then describe how various types of stress can alter telomere structure and functions. Finally, we discuss the hypothesis of stress-induced telomere signaling with hormetic effects.
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7
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Bonnell E, Pasquier E, Wellinger RJ. Telomere Replication: Solving Multiple End Replication Problems. Front Cell Dev Biol 2021; 9:668171. [PMID: 33869233 PMCID: PMC8047117 DOI: 10.3389/fcell.2021.668171] [Citation(s) in RCA: 42] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2021] [Accepted: 03/10/2021] [Indexed: 12/19/2022] Open
Abstract
Eukaryotic genomes are highly complex and divided into linear chromosomes that require end protection from unwarranted fusions, recombination, and degradation in order to maintain genomic stability. This is accomplished through the conserved specialized nucleoprotein structure of telomeres. Due to the repetitive nature of telomeric DNA, and the unusual terminal structure, namely a protruding single stranded 3′ DNA end, completing telomeric DNA replication in a timely and efficient manner is a challenge. For example, the end replication problem causes a progressive shortening of telomeric DNA at each round of DNA replication, thus telomeres eventually lose their protective capacity. This phenomenon is counteracted by the recruitment and the activation at telomeres of the specialized reverse transcriptase telomerase. Despite the importance of telomerase in providing a mechanism for complete replication of telomeric ends, the majority of telomere replication is in fact carried out by the conventional DNA replication machinery. There is significant evidence demonstrating that progression of replication forks is hampered at chromosomal ends due to telomeric sequences prone to form secondary structures, tightly DNA-bound proteins, and the heterochromatic nature of telomeres. The telomeric loop (t-loop) formed by invasion of the 3′-end into telomeric duplex sequences may also impede the passage of replication fork. Replication fork stalling can lead to fork collapse and DNA breaks, a major cause of genomic instability triggered notably by unwanted repair events. Moreover, at chromosomal ends, unreplicated DNA distal to a stalled fork cannot be rescued by a fork coming from the opposite direction. This highlights the importance of the multiple mechanisms involved in overcoming fork progression obstacles at telomeres. Consequently, numerous factors participate in efficient telomeric DNA duplication by preventing replication fork stalling or promoting the restart of a stalled replication fork at telomeres. In this review, we will discuss difficulties associated with the passage of the replication fork through telomeres in both fission and budding yeasts as well as mammals, highlighting conserved mechanisms implicated in maintaining telomere integrity during replication, thus preserving a stable genome.
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Affiliation(s)
- Erin Bonnell
- Department of Microbiology and Infectious Diseases, Faculty of Medicine and Health Sciences, Cancer Research Pavilion, Université de Sherbrooke, Sherbrooke, QC, Canada
| | - Emeline Pasquier
- Department of Microbiology and Infectious Diseases, Faculty of Medicine and Health Sciences, Cancer Research Pavilion, Université de Sherbrooke, Sherbrooke, QC, Canada
| | - Raymund J Wellinger
- Department of Microbiology and Infectious Diseases, Faculty of Medicine and Health Sciences, Cancer Research Pavilion, Université de Sherbrooke, Sherbrooke, QC, Canada
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8
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Kockler ZW, Comeron JM, Malkova A. A unified alternative telomere-lengthening pathway in yeast survivor cells. Mol Cell 2021; 81:1816-1829.e5. [PMID: 33639094 DOI: 10.1016/j.molcel.2021.02.004] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2020] [Revised: 06/28/2020] [Accepted: 02/01/2021] [Indexed: 10/24/2022]
Abstract
Alternative lengthening of telomeres (ALT) is a recombination process that maintains telomeres in the absence of telomerase and helps cancer cells to survive. Yeast has been used as a robust model of ALT; however, the inability to determine the frequency and structure of ALT survivors hinders understanding of the ALT mechanism. Here, using population and molecular genetics approaches, we overcome these problems and demonstrate that contrary to the current view, both RAD51-dependent and RAD51-independent mechanisms are required for a unified ALT survivor pathway. This conclusion is based on the calculation of ALT frequencies, as well as on ultra-long sequencing of ALT products that revealed hybrid sequences containing features attributed to both recombination pathways. Sequencing of ALT intermediates demonstrates that recombination begins with Rad51-mediated strand invasion to form DNA substrates that are matured by a Rad51-independent ssDNA annealing pathway. A similar unified ALT pathway may operate in other organisms, including humans.
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Affiliation(s)
- Zachary W Kockler
- Department of Biology, University of Iowa, Iowa City, IA 52245, USA; Interdisciplinary Graduate Program in Genetics, University of Iowa, Iowa City, IA 52245, USA
| | - Josep M Comeron
- Department of Biology, University of Iowa, Iowa City, IA 52245, USA; Interdisciplinary Graduate Program in Genetics, University of Iowa, Iowa City, IA 52245, USA.
| | - Anna Malkova
- Department of Biology, University of Iowa, Iowa City, IA 52245, USA; Interdisciplinary Graduate Program in Genetics, University of Iowa, Iowa City, IA 52245, USA.
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9
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Wu ZJ, Liu JC, Man X, Gu X, Li TY, Cai C, He MH, Shao Y, Lu N, Xue X, Qin Z, Zhou JQ. Cdc13 is predominant over Stn1 and Ten1 in preventing chromosome end fusions. eLife 2020; 9:53144. [PMID: 32755541 PMCID: PMC7406354 DOI: 10.7554/elife.53144] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2019] [Accepted: 06/12/2020] [Indexed: 12/16/2022] Open
Abstract
Telomeres define the natural ends of eukaryotic chromosomes and are crucial for chromosomal stability. The budding yeast Cdc13, Stn1 and Ten1 proteins form a heterotrimeric complex, and the inactivation of any of its subunits leads to a uniformly lethal phenotype due to telomere deprotection. Although Cdc13, Stn1 and Ten1 seem to belong to an epistasis group, it remains unclear whether they function differently in telomere protection. Here, we employed the single-linear-chromosome yeast SY14, and surprisingly found that the deletion of CDC13 leads to telomere erosion and intrachromosome end-to-end fusion, which depends on Rad52 but not Yku. Interestingly, the emergence frequency of survivors in the SY14 cdc13Δ mutant was ~29 fold higher than that in either the stn1Δ or ten1Δ mutant, demonstrating a predominant role of Cdc13 in inhibiting telomere fusion. Chromosomal fusion readily occurred in the telomerase-null SY14 strain, further verifying the default role of intact telomeres in inhibiting chromosome fusion.
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Affiliation(s)
- Zhi-Jing Wu
- The State Key Laboratory of Molecular Biology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences; University of Chinese Academy of Sciences, Shanghai, China
| | - Jia-Cheng Liu
- The State Key Laboratory of Molecular Biology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences; University of Chinese Academy of Sciences, Shanghai, China
| | - Xin Man
- The State Key Laboratory of Molecular Biology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences; University of Chinese Academy of Sciences, Shanghai, China
| | - Xin Gu
- The State Key Laboratory of Molecular Biology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences; University of Chinese Academy of Sciences, Shanghai, China
| | - Ting-Yi Li
- The State Key Laboratory of Molecular Biology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences; University of Chinese Academy of Sciences, Shanghai, China
| | - Chen Cai
- The State Key Laboratory of Molecular Biology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences; University of Chinese Academy of Sciences, Shanghai, China.,School of Life Science and Technology, ShanghaiTech University, Shanghai, China
| | - Ming-Hong He
- The State Key Laboratory of Molecular Biology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences; University of Chinese Academy of Sciences, Shanghai, China
| | - Yangyang Shao
- Key Laboratory of Synthetic Biology, CAS Center for Excellence in Molecular Plant Sciences, Shanghai Institute of Plant Physiology and Ecology, Chinese Academy of Sciences; University of Chinese Academy of Sciences, Shanghai, China
| | - Ning Lu
- Key Laboratory of Synthetic Biology, CAS Center for Excellence in Molecular Plant Sciences, Shanghai Institute of Plant Physiology and Ecology, Chinese Academy of Sciences; University of Chinese Academy of Sciences, Shanghai, China
| | - Xiaoli Xue
- Key Laboratory of Synthetic Biology, CAS Center for Excellence in Molecular Plant Sciences, Shanghai Institute of Plant Physiology and Ecology, Chinese Academy of Sciences; University of Chinese Academy of Sciences, Shanghai, China
| | - Zhongjun Qin
- Key Laboratory of Synthetic Biology, CAS Center for Excellence in Molecular Plant Sciences, Shanghai Institute of Plant Physiology and Ecology, Chinese Academy of Sciences; University of Chinese Academy of Sciences, Shanghai, China
| | - Jin-Qiu Zhou
- The State Key Laboratory of Molecular Biology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences; University of Chinese Academy of Sciences, Shanghai, China.,School of Life Science and Technology, ShanghaiTech University, Shanghai, China
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10
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Srinivas N, Rachakonda S, Kumar R. Telomeres and Telomere Length: A General Overview. Cancers (Basel) 2020; 12:E558. [PMID: 32121056 PMCID: PMC7139734 DOI: 10.3390/cancers12030558] [Citation(s) in RCA: 129] [Impact Index Per Article: 32.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2020] [Revised: 02/24/2020] [Accepted: 02/26/2020] [Indexed: 02/06/2023] Open
Abstract
Telomeres are highly conserved tandem nucleotide repeats that include proximal double-stranded and distal single-stranded regions that in complex with shelterin proteins afford protection at chromosomal ends to maintain genomic integrity. Due to the inherent limitations of DNA replication and telomerase suppression in most somatic cells, telomeres undergo age-dependent incremental attrition. Short or dysfunctional telomeres are recognized as DNA double-stranded breaks, triggering cells to undergo replicative senescence. Telomere shortening, therefore, acts as a counting mechanism that drives replicative senescence by limiting the mitotic potential of cells. Telomere length, a complex hereditary trait, is associated with aging and age-related diseases. Epidemiological data, in general, support an association with varying magnitudes between constitutive telomere length and several disorders, including cancers. Telomere attrition is also influenced by oxidative damage and replicative stress caused by genetic, epigenetic, and environmental factors. Several single nucleotide polymorphisms at different loci, identified through genome-wide association studies, influence inter-individual variation in telomere length. In addition to genetic factors, environmental factors also influence telomere length during growth and development. Telomeres hold potential as biomarkers that reflect the genetic predisposition together with the impact of environmental conditions and as targets for anti-cancer therapies.
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Affiliation(s)
| | | | - Rajiv Kumar
- Division of Functional Genome Analysis, German Cancer Research Center, Im Neunheimer Feld 580, 69120 Heidelberg, Germany; (N.S.); (S.R.)
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11
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Xu Z, Teixeira MT. The many types of heterogeneity in replicative senescence. Yeast 2019; 36:637-648. [PMID: 31306505 PMCID: PMC6900063 DOI: 10.1002/yea.3433] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2019] [Revised: 07/04/2019] [Accepted: 07/07/2019] [Indexed: 11/10/2022] Open
Abstract
Replicative senescence, which is induced by telomere shortening, underlies the loss of regeneration capacity of organs and is ultimately detrimental to the organism. At the same time, it is required to protect organisms from unlimited cell proliferation that may arise from numerous stimuli or deregulations. One important feature of replicative senescence is its high level of heterogeneity and asynchrony, which promote genome instability and senescence escape. Characterizing this heterogeneity and investigating its sources are thus critical to understanding the robustness of replicative senescence. Here we review the different aspects of senescence driven by telomere attrition that are subject to variation in Saccharomyces cerevisiae, the current understanding of the molecular processes at play, and the consequences of heterogeneity in replicative senescence.
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Affiliation(s)
- Zhou Xu
- CNRS, UMR7238, Institut de Biologie Paris‐Seine, Laboratory of Computational and Quantitative BiologySorbonne UniversitéParisFrance
| | - Maria Teresa Teixeira
- CNRS, UMR8226, Institut de Biologie Physico‐Chimique, Laboratory of Molecular and Cell Biology of EukaryotesSorbonne Université, PSL Research UniversityParisFrance
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12
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Armstrong CA, Moiseeva V, Collopy LC, Pearson SR, Ullah TR, Xi ST, Martin J, Subramaniam S, Marelli S, Amelina H, Tomita K. Fission yeast Ccq1 is a modulator of telomerase activity. Nucleic Acids Res 2019; 46:704-716. [PMID: 29216371 PMCID: PMC5778466 DOI: 10.1093/nar/gkx1223] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2017] [Accepted: 11/27/2017] [Indexed: 01/05/2023] Open
Abstract
Shelterin, the telomeric protein complex, plays a crucial role in telomere homeostasis. In fission yeast, telomerase is recruited to chromosome ends by the shelterin component Tpz1 and its binding partner Ccq1, where telomerase binds to the 3' overhang to add telomeric repeats. Recruitment is initiated by the interaction of Ccq1 with the telomerase subunit Est1. However, how telomerase is released following elongation remains to be established. Here, we show that Ccq1 also has a role in the suppression of telomere elongation, when coupled with the Clr4 histone H3 methyl-transferase complex and the Clr3 histone deacetylase and nucleosome remodelling complex, SHREC. We have dissected the functions of Ccq1 by establishing a Ccq1-Est1 fusion system, which bypasses the telomerase recruitment step. We demonstrate that Ccq1 forms two distinct complexes for positive and negative telomerase regulation, with Est1 and Clr3 respectively. The negative form of Ccq1 promotes dissociation of Ccq1-telomerase from Tpz1, thereby restricting local telomerase activity. The Clr4 complex also has a negative regulation activity with Ccq1, independently of SHREC. Thus, we propose a model in which Ccq1-Est1 recruits telomerase to mediate telomere extension, whilst elongated telomeric DNA recruits Ccq1 with the chromatin-remodelling complexes, which in turn releases telomerase from the telomere.
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Affiliation(s)
- Christine A Armstrong
- Chromosome Maintenance Group, UCL Cancer Institute, University College London, London WC1E 6DD, UK
| | - Vera Moiseeva
- Chromosome Maintenance Group, UCL Cancer Institute, University College London, London WC1E 6DD, UK
| | - Laura C Collopy
- Chromosome Maintenance Group, UCL Cancer Institute, University College London, London WC1E 6DD, UK
| | - Siân R Pearson
- Chromosome Maintenance Group, UCL Cancer Institute, University College London, London WC1E 6DD, UK
| | - Tomalika R Ullah
- Chromosome Maintenance Group, UCL Cancer Institute, University College London, London WC1E 6DD, UK.,MSc Human Molecular Genetics, Faculty of Medicine, Imperial College London, London SW7 2AZ, UK
| | - Shidong T Xi
- Chromosome Maintenance Group, UCL Cancer Institute, University College London, London WC1E 6DD, UK.,Faculty of Life Sciences, University College London, London WC1E 6BT, UK
| | - Jennifer Martin
- Chromosome Maintenance Group, UCL Cancer Institute, University College London, London WC1E 6DD, UK.,MSc Human Molecular Genetics, Faculty of Medicine, Imperial College London, London SW7 2AZ, UK
| | - Shaan Subramaniam
- Chromosome Maintenance Group, UCL Cancer Institute, University College London, London WC1E 6DD, UK.,Faculty of Life Sciences, University College London, London WC1E 6BT, UK
| | - Sara Marelli
- Chromosome Maintenance Group, UCL Cancer Institute, University College London, London WC1E 6DD, UK
| | - Hanna Amelina
- Chromosome Maintenance Group, UCL Cancer Institute, University College London, London WC1E 6DD, UK
| | - Kazunori Tomita
- Chromosome Maintenance Group, UCL Cancer Institute, University College London, London WC1E 6DD, UK
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13
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Jolivet P, Serhal K, Graf M, Eberhard S, Xu Z, Luke B, Teixeira MT. A subtelomeric region affects telomerase-negative replicative senescence in Saccharomyces cerevisiae. Sci Rep 2019; 9:1845. [PMID: 30755624 PMCID: PMC6372760 DOI: 10.1038/s41598-018-38000-9] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2018] [Accepted: 12/04/2018] [Indexed: 11/21/2022] Open
Abstract
In eukaryotes, telomeres determine cell proliferation potential by triggering replicative senescence in the absence of telomerase. In Saccharomyces cerevisiae, senescence is mainly dictated by the first telomere that reaches a critically short length, activating a DNA-damage-like response. How the corresponding signaling is modulated by the telomeric structure and context is largely unknown. Here we investigated how subtelomeric elements of the shortest telomere in a telomerase-negative cell influence the onset of senescence. We found that a 15 kb truncation of the 7L subtelomere widely used in studies of telomere biology affects cell growth when combined with telomerase inactivation. This effect is likely not explained by (i) elimination of sequence homology at chromosome ends that would compromise homology-directed DNA repair mechanisms; (ii) elimination of the conserved subtelomeric X-element; (iii) elimination of a gene that would become essential in the absence of telomerase; and (iv) heterochromatinization of inner genes, causing the silencing of an essential gene in replicative senescent cells. This works contributes to better delineate subtelomere functions and their impact on telomere biology.
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Affiliation(s)
- Pascale Jolivet
- Sorbonne Université, PSL, CNRS, UMR8226, Institut de Biologie Physico-Chimique, Laboratoire de Biologie Moléculaire et Cellulaire des Eucaryotes, F-75005, Paris, France
| | - Kamar Serhal
- Sorbonne Université, PSL, CNRS, UMR8226, Institut de Biologie Physico-Chimique, Laboratoire de Biologie Moléculaire et Cellulaire des Eucaryotes, F-75005, Paris, France.,Institut de Génétique Humaine, CNRS, Université Montpellier, Montpellier, France
| | - Marco Graf
- Institute of Molecular Biology (IMB), 55128, Mainz, Germany
| | - Stephan Eberhard
- Sorbonne Université, PSL, CNRS, UMR7141, Institut de Biologie Physico-Chimique, Laboratoire de Physiologie Moléculaire et Membranaire du Chloroplaste, F-75005, Paris, France
| | - Zhou Xu
- Sorbonne Université, PSL, CNRS, UMR8226, Institut de Biologie Physico-Chimique, Laboratoire de Biologie Moléculaire et Cellulaire des Eucaryotes, F-75005, Paris, France
| | - Brian Luke
- Institute of Neurobiology and Developmental Biology, JGU Mainz, Ackermannweg 4, 55128, Mainz, Germany.,Institute of Molecular Biology (IMB), 55128, Mainz, Germany
| | - Maria Teresa Teixeira
- Sorbonne Université, PSL, CNRS, UMR8226, Institut de Biologie Physico-Chimique, Laboratoire de Biologie Moléculaire et Cellulaire des Eucaryotes, F-75005, Paris, France.
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14
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Fontana GA, Reinert JK, Thomä NH, Rass U. Shepherding DNA ends: Rif1 protects telomeres and chromosome breaks. MICROBIAL CELL 2018; 5:327-343. [PMID: 29992129 PMCID: PMC6035837 DOI: 10.15698/mic2018.07.639] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Cells have evolved conserved mechanisms to protect DNA ends, such as those at the termini of linear chromosomes, or those at DNA double-strand breaks (DSBs). In eukaryotes, DNA ends at chromosomal termini are packaged into proteinaceous structures called telomeres. Telomeres protect chromosome ends from erosion, inadvertent activation of the cellular DNA damage response (DDR), and telomere fusion. In contrast, cells must respond to damage-induced DNA ends at DSBs by harnessing the DDR to restore chromosome integrity, avoiding genome instability and disease. Intriguingly, Rif1 (Rap1-interacting factor 1) has been implicated in telomere homeostasis as well as DSB repair. The protein was first identified in Saccharomyces cerevisiae as being part of the proteinaceous telosome. In mammals, RIF1 is not associated with intact telomeres, but was found at chromosome breaks, where RIF1 has emerged as a key mediator of pathway choice between the two evolutionary conserved DSB repair pathways of non-homologous end-joining (NHEJ) and homologous recombination (HR). While this functional dichotomy has long been a puzzle, recent findings link yeast Rif1 not only to telomeres, but also to DSB repair, and mechanistic parallels likely exist. In this review, we will provide an overview of the actions of Rif1 at DNA ends and explore how exclusion of end-processing factors might be the underlying principle allowing Rif1 to fulfill diverse biological roles at telomeres and chromosome breaks.
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Affiliation(s)
- Gabriele A Fontana
- Friedrich Miescher Institute for Biomedical Research, Maulbeerstrasse 66, CH-4058 Basel, Switzerland
| | - Julia K Reinert
- Friedrich Miescher Institute for Biomedical Research, Maulbeerstrasse 66, CH-4058 Basel, Switzerland.,University of Basel, Petersplatz 10, CH-4003 Basel, Switzerland
| | - Nicolas H Thomä
- Friedrich Miescher Institute for Biomedical Research, Maulbeerstrasse 66, CH-4058 Basel, Switzerland
| | - Ulrich Rass
- Friedrich Miescher Institute for Biomedical Research, Maulbeerstrasse 66, CH-4058 Basel, Switzerland
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15
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Abstract
Telomere length is maintained in most eukaryotes by the action of a specialized enzyme, the telomerase. However, the complexity of mechanisms regulating telomeric DNA length as well as the heterogeneity in length of each telomere in a population of cells has made it very difficult to understand how telomerase is regulated in vivo. Here, we describe a method developed in Saccharomyces cerevisiae to monitor the addition of telomeric sequences to a single newly generated telomere in vivo. The primary strain consists of a HO endonuclease cleavage site that is placed directly adjacent to an 81-base-pair stretch of telomeric DNA inserted into the ADH4 locus of chromosome VII. Upon cleavage by HO, the de novo DNA end is rapidly healed by the telomerase enzyme and the analysis of this process allows to gain a mechanistic understanding of how telomerase action is regulated in the cell.
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Affiliation(s)
- Diego Bonetti
- Institute for Molecular Biology (IMB) gGMBH, Ackermannweg 4, 55128, Mainz, Germany.
- Dipartimento di Biotecnologie e Bioscienze, Università di Milano-Bicocca, Milano, Italy.
| | - Maria Pia Longhese
- Dipartimento di Biotecnologie e Bioscienze, Università di Milano-Bicocca, Milano, Italy
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16
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Harari Y, Kupiec M. Mec1 ATR is needed for extensive telomere elongation in response to ethanol in yeast. Curr Genet 2017; 64:223-234. [PMID: 28780613 DOI: 10.1007/s00294-017-0728-1] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2017] [Revised: 07/26/2017] [Accepted: 07/31/2017] [Indexed: 11/26/2022]
Abstract
Telomere length homeostasis is essential for cell survival. In humans, telomeres shorten as a function of age. Short telomeres are known determinants of cell senescence and longevity. The yeast Saccharomyces cerevisiae expresses telomerase and maintains a strict telomere length homeostasis during vegetative growth. We have previously reported that different environmental signals promote changes in telomere length in S. cerevisiae. In particular, exposure to ethanol induces an extensive telomere elongation response due to a reduction in RAP1 mRNA and protein levels. Here we show that the reduction in Rap1 protein levels disrupts the physical interaction between Rap1 and Rif1, which in turn reduces the recruitment of these two proteins to telomeres during G2-phase. Although elongation of the shortest telomeres has been shown to depend on the Rif2 telomeric protein and on the Tel1(ATM) protein kinase, we show here that the extensive telomere elongation in response to ethanol exposure is Rif1 and Mec1 (ATR)-dependent. Our results fit a model in which Rif1 and Rap1 form a complex that is loaded onto telomeres at the end of S-phase. Reduced levels of the Rap1-Rif1 complex in ethanol lead to continuous telomere elongation in a Mec1-dependent process.
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Affiliation(s)
- Yaniv Harari
- Department of Molecular Microbiology and Biotechnology, Tel Aviv University, Ramat Aviv, Tel Aviv, Israel
| | - Martin Kupiec
- Department of Molecular Microbiology and Biotechnology, Tel Aviv University, Ramat Aviv, Tel Aviv, Israel.
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17
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Graf M, Bonetti D, Lockhart A, Serhal K, Kellner V, Maicher A, Jolivet P, Teixeira MT, Luke B. Telomere Length Determines TERRA and R-Loop Regulation through the Cell Cycle. Cell 2017; 170:72-85.e14. [DOI: 10.1016/j.cell.2017.06.006] [Citation(s) in RCA: 128] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2017] [Revised: 04/21/2017] [Accepted: 06/06/2017] [Indexed: 10/19/2022]
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18
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Abstract
In this Hypothesis, Greider describes a new model for telomere length regulation, which links DNA replication and telomere elongation. Telomere length is regulated around an equilibrium set point. Telomeres shorten during replication and are lengthened by telomerase. Disruption of the length equilibrium leads to disease; thus, it is important to understand the mechanisms that regulate length at the molecular level. The prevailing protein-counting model for regulating telomerase access to elongate the telomere does not explain accumulating evidence of a role of DNA replication in telomere length regulation. Here I present an alternative model: the replication fork model that can explain how passage of a replication fork and regulation of origin firing affect telomere length.
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Affiliation(s)
- Carol W Greider
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA; Department of Biology, Johns Hopkins University, Baltimore, Maryland 21218, USA
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19
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Larcher MV, Pasquier E, MacDonald RS, Wellinger RJ. Ku Binding on Telomeres Occurs at Sites Distal from the Physical Chromosome Ends. PLoS Genet 2016; 12:e1006479. [PMID: 27930670 PMCID: PMC5145143 DOI: 10.1371/journal.pgen.1006479] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2016] [Accepted: 11/14/2016] [Indexed: 01/28/2023] Open
Abstract
The Ku complex binds non-specifically to DNA breaks and ensures repair via NHEJ. However, Ku is also known to bind directly to telomeric DNA ends and its presence there is associated with telomere capping, but avoiding NHEJ. How the complex discriminates between a DNA break and a telomeric extremity remains unknown. Our results using a tagged Ku complex, or a chromosome end capturing method, in budding yeast show that yKu association with telomeres can occur at sites distant from the physical end, on sub-telomeric elements, as well as on interstitial telomeric repeats. Consistent with previous studies, our results also show that yKu associates with telomeres in two distinct and independent ways: either via protein-protein interactions between Yku80 and Sir4 or via direct DNA binding. Importantly, yKu associates with the new sites reported here via both modes. Therefore, in sir4Δ cells, telomere bound yKu molecules must have loaded from a DNA-end near the transition of non-telomeric to telomeric repeat sequences. Such ends may have been one sided DNA breaks that occur as a consequence of stalled replication forks on or near telomeric repeat DNA. Altogether, the results predict a new model for yKu function at telomeres that involves yKu binding at one-sided DNA breaks caused by replication stalling. On telomere proximal chromatin, this binding is not followed by initiation of non-homologous end-joining, but rather by break-induced replication or repeat elongation by telomerase. After repair, the yKu-distal portion of telomeres is bound by Rap1, which in turn reduces the potential for yKu to mediate NHEJ. These results thus propose a solution to a long-standing conundrum, namely how to accommodate the apparently conflicting functions of Ku on telomeres. The Ku complex binds to and mediates the rejoining of two DNA ends that were generated by a double-stranded DNA break in the genome. However, Ku is known to be present at telomeres as well. If it would induce end-to-end joining there, it would create chromosome end-fusions that inevitably will lead to gross chromosome rearrangements and genome instability, common hallmarks for cancer initiation. Our results here show that Ku actually is associated with sites on telomeric regions that are distant from the physical ends of the chromosomes. We propose that this association serves to rescue DNA replication that has difficulty passing through telomeric chromatin. If so called one-sided breaks occur near or in telomeric repeats, they will generate critically short telomeres that need to be elongated. The binding of Ku may thus either facilitate the establishment of a specialized end-copying mechanism, called break induced replication or aid in recruiting telomerase to the short ends. These findings thus propose ways to potential solutions for the major conceptual problem that arose with the finding that Ku is associated with telomeres.
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Affiliation(s)
- Mélanie V. Larcher
- Department of Microbiology and Infectious Diseases, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, Canada
| | - Emeline Pasquier
- Department of Microbiology and Infectious Diseases, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, Canada
| | - R. Stephen MacDonald
- Department of Microbiology and Infectious Diseases, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, Canada
| | - Raymund J. Wellinger
- Department of Microbiology and Infectious Diseases, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, Canada
- * E-mail:
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20
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Heidenreich B, Kumar R. TERT promoter mutations in telomere biology. MUTATION RESEARCH-REVIEWS IN MUTATION RESEARCH 2016; 771:15-31. [PMID: 28342451 DOI: 10.1016/j.mrrev.2016.11.002] [Citation(s) in RCA: 130] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/24/2016] [Accepted: 11/10/2016] [Indexed: 02/07/2023]
Abstract
Telomere repeats at chromosomal ends, critical to genome integrity, are maintained through an elaborate network of proteins and pathways. Shelterin complex proteins shield telomeres from induction of DNA damage response to overcome end protection problem. A specialized ribonucleic protein, telomerase, maintains telomere homeostasis through repeat addition to counter intrinsic shortcomings of DNA replication that leads to gradual sequence shortening in successive mitoses. The biogenesis and recruitment of telomerase composed of telomerase reverse transcriptase (TERT) subunit and an RNA component, takes place through the intricate machinery that involves an elaborate number of molecules. The synthesis of telomeres remains a controlled and limited process. Inherited mutations in the molecules involved in the process directly or indirectly cause telomeropathies. Telomerase, while present in stem cells, is deactivated due to epigenetic silencing of the rate-limiting TERT upon differentiation in most of somatic cells with a few exceptions. However, in most of the cancer cells telomerase reactivation remains a ubiquitous process and constitutes one of the major hallmarks. Discovery of mutations within the core promoter of the TERT gene that create de novo binding sites for E-twenty-six (ETS) transcription factors provided a mechanism for cancer-specific telomerase reactivation. The TERT promoter mutations occur mainly in tumors from tissues with low rates of self-renewal. In melanoma, glioma, hepatocellular carcinoma, urothelial carcinoma and others, the promoter mutations have been shown to define subsets of patients with adverse disease outcomes, associate with increased transcription of TERT, telomerase reactivation and affect telomere length; in stem cells the mutations inhibit TERT silencing following differentiation into adult cells. The TERT promoter mutations cause an epigenetic switch on the mutant allele along with recruitment of pol II following the binding of GABPA/B1 complex that leads to mono-allelic expression. Thus, the TERT promoter mutations hold potential as biomarkers as well as future therapeutic targets.
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Affiliation(s)
| | - Rajiv Kumar
- Division of Molecular Genetic Epidemiology; German Consortium for Translational Cancer Research (DKTK), German Cancer Research Center, 69120 Heidelberg, Germany.
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21
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Simon MN, Churikov D, Géli V. Replication stress as a source of telomere recombination during replicative senescence in Saccharomyces cerevisiae. FEMS Yeast Res 2016; 16:fow085. [PMID: 27683094 DOI: 10.1093/femsyr/fow085] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/27/2016] [Indexed: 12/25/2022] Open
Abstract
Replicative senescence is triggered by short unprotected telomeres that arise in the absence of telomerase. In addition, telomeres are known as difficult regions to replicate due to their repetitive G-rich sequence prone to secondary structures and tightly bound non-histone proteins. Here we review accumulating evidence that telomerase inactivation in yeast immediately unmasks the problems associated with replication stress at telomeres. Early after telomerase inactivation, yeast cells undergo successive rounds of stochastic DNA damages and become dependent on recombination for viability long before the bulk of telomeres are getting critically short. The switch from telomerase to recombination to repair replication stress-induced damage at telomeres creates telomere instability, which may drive further genomic alterations and prepare the ground for telomerase-independent immortalization observed in yeast survivors and in 15% of human cancer.
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Affiliation(s)
- Marie-Noëlle Simon
- Centre de Recherche en Cancérologie de Marseille, 'Equipe labellisée Ligue Contre le Cancer', Inserm U1068, Marseille F-13009, France; CNRS, UMR7258, Marseille F-13009; Institut Paoli-Calmettes, Marseille F-13009, France; Aix-Marseille University, UM 105, Marseille F-13284, France
| | - Dmitri Churikov
- Centre de Recherche en Cancérologie de Marseille, 'Equipe labellisée Ligue Contre le Cancer', Inserm U1068, Marseille F-13009, France; CNRS, UMR7258, Marseille F-13009; Institut Paoli-Calmettes, Marseille F-13009, France; Aix-Marseille University, UM 105, Marseille F-13284, France
| | - Vincent Géli
- Centre de Recherche en Cancérologie de Marseille, 'Equipe labellisée Ligue Contre le Cancer', Inserm U1068, Marseille F-13009, France; CNRS, UMR7258, Marseille F-13009; Institut Paoli-Calmettes, Marseille F-13009, France; Aix-Marseille University, UM 105, Marseille F-13284, France
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22
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Multiple Rad52-Mediated Homology-Directed Repair Mechanisms Are Required to Prevent Telomere Attrition-Induced Senescence in Saccharomyces cerevisiae. PLoS Genet 2016; 12:e1006176. [PMID: 27428329 PMCID: PMC4948829 DOI: 10.1371/journal.pgen.1006176] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2016] [Accepted: 06/15/2016] [Indexed: 12/15/2022] Open
Abstract
Most human somatic cells express insufficient levels of telomerase, which can result in telomere shortening and eventually senescence, both of which are hallmarks of ageing. Homology-directed repair (HDR) is important for maintaining proper telomere function in yeast and mammals. In Saccharomyces cerevisiae, Rad52 is required for almost all HDR mechanisms, and telomerase-null cells senesce faster in the absence of Rad52. However, its role in preventing accelerated senescence has been unclear. In this study, we make use of rad52 separation-of-function mutants to find that multiple Rad52-mediated HDR mechanisms are required to delay senescence, including break-induced replication and sister chromatid recombination. In addition, we show that misregulation of histone 3 lysine 56 acetylation, which is known to be defective in sister chromatid recombination, also causes accelerated senescence. We propose a model where Rad52 is needed to repair telomere attrition-induced replication stress. Telomeres are essential structures located at the ends of chromosomes. The canonical DNA replication machinery is unable to fully replicate DNA at chromosome ends, causing telomeres to shorten with every round of cell division. This shortening can be counteracted by an enzyme called telomerase, but in most human somatic cells, there is insufficient expression of telomerase to prevent telomere shortening. Cells with critically short telomeres can enter an arrested state known as senescence. Telomere attrition has been identified as a hallmark of human ageing. Homologous recombination proteins are important for proper telomere function in yeast and mammals. Yeast lacking both telomerase and Rad52, required for almost all recombination, exhibits accelerated senescence, yet no apparent increase in the rate of telomere shortening. In this study, we explore the role of Rad52 during senescence by taking advantage of rad52 separation-of-function mutants. We find that Rad52 acts in multiple ways to overcome DNA replication problems at telomeres. Impediments to telomere replication can be dealt with by post-replication repair mechanisms, which use a newly synthesized sister chromatid as a template to replicate past the impediment, while telomere truncations, likely caused by the collapse of replication forks, can be extended by break-induced replication.
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23
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Abstract
The conserved shelterin complex is critical for chromosome capping and maintaining telomere length homeostasis. Using a combination of deletions, fusions and tethers, Pan et al. define key elements of shelterin important for telomere length regulation. The conserved shelterin complex is critical for chromosome capping and maintaining telomere length homeostasis. In fission yeast, shelterin is comprised of five proteins. Taz1, Rap1, and Poz1 function as negative regulators of telomere elongation, whereas Pot1 and Tpz1 are critical for end capping and telomerase recruitment. How the five proteins work together to safeguard chromosome ends and promote telomere length homeostasis is a matter of great interest. Using a combination of deletions, fusions, and tethers, we define key elements of shelterin important for telomere length regulation. Surprisingly, deletion of the entire Rap1 and Poz1 proteins does not impair telomere length regulation as long as a static bridge is provided between Taz1 and Tpz1. Cells harboring minishelterin display wild-type telomere length and intact subtelomeric silencing. However, protection against end fusions in G1 is compromised in the absence of Rap1. Our data reveal a remarkable plasticity in shelterin architecture and separate functions in length regulation and end protection.
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24
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Goto GH, Zencir S, Hirano Y, Ogi H, Ivessa A, Sugimoto K. Binding of Multiple Rap1 Proteins Stimulates Chromosome Breakage Induction during DNA Replication. PLoS Genet 2015; 11:e1005283. [PMID: 26263073 PMCID: PMC4532487 DOI: 10.1371/journal.pgen.1005283] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2014] [Accepted: 05/14/2015] [Indexed: 02/07/2023] Open
Abstract
Telomeres, the ends of linear eukaryotic chromosomes, have a specialized chromatin structure that provides a stable chromosomal terminus. In budding yeast Rap1 protein binds to telomeric TG repeat and negatively regulates telomere length. Here we show that binding of multiple Rap1 proteins stimulates DNA double-stranded break (DSB) induction at both telomeric and non-telomeric regions. Consistent with the role of DSB induction, Rap1 stimulates nearby recombination events in a dosage-dependent manner. Rap1 recruits Rif1 and Rif2 to telomeres, but neither Rif1 nor Rif2 is required for DSB induction. Rap1-mediated DSB induction involves replication fork progression but inactivation of checkpoint kinase Mec1 does not affect DSB induction. Rap1 tethering shortens artificially elongated telomeres in parallel with telomerase inhibition, and this telomere shortening does not require homologous recombination. These results suggest that Rap1 contributes to telomere homeostasis by promoting chromosome breakage. Telomere length is maintained primarily through equilibrium between telomerase-mediated lengthening and the loss of telomeric sequence through the end-replication problem. In budding yeast Rap1 protein binds to telomeric TG repeat and negatively regulates telomerase recruitment in a dosage-dependent manner. In this paper we provide evidence suggesting an alternative Rap1-dependent telomere shortening mechanism in which binding of multiple Rap1 proteins mediates DNA break induction during DNA replication. This process does not involve recombination events; therefore, it is distinct from loop-mediated telomere trimming.
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Affiliation(s)
- Greicy H. Goto
- Department of Microbiology, Biochemistry and Molecular Genetics, New Jersey Medical School, Rutgers, The State University of New Jersey, Newark, New Jersey, United States of America
| | - Sevil Zencir
- Department of Microbiology, Biochemistry and Molecular Genetics, New Jersey Medical School, Rutgers, The State University of New Jersey, Newark, New Jersey, United States of America
| | - Yukinori Hirano
- Department of Cell Biology and Molecular Medicine, New Jersey Medical School, Rutgers, The State University of New Jersey, Newark, New Jersey, United States of America
| | - Hiroo Ogi
- Department of Microbiology, Biochemistry and Molecular Genetics, New Jersey Medical School, Rutgers, The State University of New Jersey, Newark, New Jersey, United States of America
| | - Andreas Ivessa
- Department of Cell Biology and Molecular Medicine, New Jersey Medical School, Rutgers, The State University of New Jersey, Newark, New Jersey, United States of America
| | - Katsunori Sugimoto
- Department of Microbiology, Biochemistry and Molecular Genetics, New Jersey Medical School, Rutgers, The State University of New Jersey, Newark, New Jersey, United States of America
- Department of Cell Biology and Molecular Medicine, New Jersey Medical School, Rutgers, The State University of New Jersey, Newark, New Jersey, United States of America
- * E-mail:
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25
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Soler JJ, Ruiz Castellano C, Martínez-de la Puente J, Tomás G, Ruiz-Rodríguez M, Figuerola J. Telomere dynamics in parasitic great spotted cuckoos and their magpie hosts. J Evol Biol 2015; 28:1610-7. [DOI: 10.1111/jeb.12680] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2015] [Revised: 06/14/2015] [Accepted: 06/16/2015] [Indexed: 12/18/2022]
Affiliation(s)
- J. J. Soler
- Departamento de Ecología Funcional y Evolutiva; Estación Experimental de Zonas Áridas (CSIC); Almería Spain
| | - C. Ruiz Castellano
- Departamento de Ecología Funcional y Evolutiva; Estación Experimental de Zonas Áridas (CSIC); Almería Spain
| | | | - G. Tomás
- Departamento de Ecología Funcional y Evolutiva; Estación Experimental de Zonas Áridas (CSIC); Almería Spain
| | - M. Ruiz-Rodríguez
- Departamento de Ecología Funcional y Evolutiva; Estación Experimental de Zonas Áridas (CSIC); Almería Spain
| | - J. Figuerola
- Departamento de Ecología de Humedales; Estación Biológica Doñana (CSIC); Sevilla Spain
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26
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Kwapisz M, Ruault M, van Dijk E, Gourvennec S, Descrimes M, Taddei A, Morillon A. Expression of Subtelomeric lncRNAs Links Telomeres Dynamics to RNA Decay in S. cerevisiae. Noncoding RNA 2015; 1:94-126. [PMID: 29861418 PMCID: PMC5932542 DOI: 10.3390/ncrna1020094] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2015] [Revised: 06/17/2015] [Accepted: 06/17/2015] [Indexed: 11/24/2022] Open
Abstract
Long non-coding RNAs (lncRNAs) have been shown to regulate gene expression, chromatin domains and chromosome stability in eukaryotic cells. Recent observations have reported the existence of telomeric repeats containing long ncRNAs – TERRA in mammalian and yeast cells. However, their functions remain poorly characterized. Here, we report the existence in S. cerevisiae of several lncRNAs within Y′ subtelomeric regions. We have called them subTERRA. These belong to Cryptic Unstable Transcripts (CUTs) and Xrn1p-sensitive Unstable Transcripts (XUTs) family. subTERRA transcription, carried out mainly by RNAPII, is initiated within the subtelomeric Y’ element and occurs in both directions, towards telomeres as well as centromeres. We show that subTERRA are distinct from TERRA and are mainly degraded by the general cytoplasmic and nuclear 5′- and 3′- RNA decay pathways in a transcription-dependent manner. subTERRA accumulates preferentially during the G1/S transition and in C-terminal rap1 mutant but independently of Rap1p function in silencing. The accumulation of subTERRA in RNA decay mutants coincides with telomere misregulation: shortening of telomeres, loss of telomeric clustering in mitotic cells and changes in silencing of subtelomeric regions. Our data suggest that subtelomeric RNAs expression links telomere maintenance to RNA degradation pathways.
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Affiliation(s)
- Marta Kwapisz
- ncRNA, epigenetics and genome fluidity, Institut Curie, PSL Research University, CNRS UMR3244, Université Pierre et Marie Curie, 26 rue d’Ulm, 75248 Paris Cedex 05, France; E-Mail: (M.D.)
- Authors to whom correspondence should be addressed; E-Mails: (M.K.); (A.M.); Tel.: +33-561-335-824 (M.K.); +33-(0)-156-246-515 (A.M.); Fax: +33-524-335-886 (M.K.); +33-(0)-156-246-674 (A.M.)
| | - Myriam Ruault
- Nuclear Dynamics, Institut Curie, PSL Research University, CNRS UMR3664, Université Pierre et Marie Curie, 26 rue d’Ulm, 75248 Paris Cedex 05, France; E-Mails: (M.R.); (A.T.)
| | - Erwin van Dijk
- ncRNA, epigenetics and genome fluidity, Institut Curie, PSL Research University, CNRS UMR3244, Université Pierre et Marie Curie, 26 rue d’Ulm, 75248 Paris Cedex 05, France; E-Mail: (M.D.)
| | - Stephanie Gourvennec
- ncRNA, epigenetics and genome fluidity, Institut Curie, PSL Research University, CNRS UMR3244, Université Pierre et Marie Curie, 26 rue d’Ulm, 75248 Paris Cedex 05, France; E-Mail: (M.D.)
| | - Marc Descrimes
- ncRNA, epigenetics and genome fluidity, Institut Curie, PSL Research University, CNRS UMR3244, Université Pierre et Marie Curie, 26 rue d’Ulm, 75248 Paris Cedex 05, France; E-Mail: (M.D.)
| | - Angela Taddei
- Nuclear Dynamics, Institut Curie, PSL Research University, CNRS UMR3664, Université Pierre et Marie Curie, 26 rue d’Ulm, 75248 Paris Cedex 05, France; E-Mails: (M.R.); (A.T.)
| | - Antonin Morillon
- ncRNA, epigenetics and genome fluidity, Institut Curie, PSL Research University, CNRS UMR3244, Université Pierre et Marie Curie, 26 rue d’Ulm, 75248 Paris Cedex 05, France; E-Mail: (M.D.)
- Authors to whom correspondence should be addressed; E-Mails: (M.K.); (A.M.); Tel.: +33-561-335-824 (M.K.); +33-(0)-156-246-515 (A.M.); Fax: +33-524-335-886 (M.K.); +33-(0)-156-246-674 (A.M.)
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The pif1 helicase, a negative regulator of telomerase, acts preferentially at long telomeres. PLoS Genet 2015; 11:e1005186. [PMID: 25906395 PMCID: PMC4408051 DOI: 10.1371/journal.pgen.1005186] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2015] [Accepted: 03/30/2015] [Indexed: 11/19/2022] Open
Abstract
Telomerase, the enzyme that maintains telomeres, preferentially lengthens short telomeres. The S. cerevisiae Pif1 DNA helicase inhibits both telomerase-mediated telomere lengthening and de novo telomere addition at double strand breaks (DSB). Here, we report that the association of the telomerase subunits Est2 and Est1 at a DSB was increased in the absence of Pif1, as it is at telomeres, suggesting that Pif1 suppresses de novo telomere addition by removing telomerase from the break. To determine how the absence of Pif1 results in telomere lengthening, we used the single telomere extension assay (STEX), which monitors lengthening of individual telomeres in a single cell cycle. In the absence of Pif1, telomerase added significantly more telomeric DNA, an average of 72 nucleotides per telomere compared to the 45 nucleotides in wild type cells, and the fraction of telomeres lengthened increased almost four-fold. Using an inducible short telomere assay, Est2 and Est1 no longer bound preferentially to a short telomere in pif1 mutant cells while binding of Yku80, a telomere structural protein, was unaffected by the status of the PIF1 locus. Two experiments demonstrate that Pif1 binding is affected by telomere length: Pif1 (but not Yku80) -associated telomeres were 70 bps longer than bulk telomeres, and in the inducible short telomere assay, Pif1 bound better to wild type length telomeres than to short telomeres. Thus, preferential lengthening of short yeast telomeres is achieved in part by targeting the negative regulator Pif1 to long telomeres. Telomerase, the enzyme that maintains telomeres, preferentially lengthens short telomeres. The baker’s yeast Pif1 DNA helicase inhibits both telomerase-mediated lengthening of existing telomeres and the formation of new telomeres at double strand breaks. By virtue of its ATPase activity, Pif1 reduces the level of telomerase binding to telomeres. Here, we report that the association of the telomerase subunits Est2 and Est1 at a DNA break was increased in the absence of Pif1, suggesting that Pif1 affects telomere length and new telomere formation by similar mechanisms. In cells lacking Pif1, Est2 and Est1 no longer bound preferentially to short telomeres, a larger fraction of telomeres was lengthened and the amount of telomeric DNA added per telomere was increased compared to wild type cells. Furthermore, by two different assays, Pif1 bound preferentially to long telomeres in vivo. Thus, preferential lengthening of short telomeres is achieved in part by targeting Pif1, a negative regulator of telomerase, to long telomeres.
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Fulcher N, Teubenbacher A, Kerdaffrec E, Farlow A, Nordborg M, Riha K. Genetic architecture of natural variation of telomere length in Arabidopsis thaliana. Genetics 2015; 199:625-35. [PMID: 25488978 PMCID: PMC4317667 DOI: 10.1534/genetics.114.172163] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2014] [Accepted: 11/25/2014] [Indexed: 11/18/2022] Open
Abstract
Telomeres represent the repetitive sequences that cap chromosome ends and are essential for their protection. Telomere length is known to be highly heritable and is derived from a homeostatic balance between telomeric lengthening and shortening activities. Specific loci that form the genetic framework underlying telomere length homeostasis, however, are not well understood. To investigate the extent of natural variation of telomere length in Arabidopsis thaliana, we examined 229 worldwide accessions by terminal restriction fragment analysis. The results showed a wide range of telomere lengths that are specific to individual accessions. To identify loci that are responsible for this variation, we adopted a quantitative trait loci (QTL) mapping approach with multiple recombinant inbred line (RIL) populations. A doubled haploid RIL population was first produced using centromere-mediated genome elimination between accessions with long (Pro-0) and intermediate (Col-0) telomere lengths. Composite interval mapping analysis of this population along with two established RIL populations (Ler-2/Cvi-0 and Est-1/Col-0) revealed a number of shared and unique QTL. QTL detected in the Ler-2/Cvi-0 population were examined using near isogenic lines that confirmed causative regions on chromosomes 1 and 2. In conclusion, this work describes the extent of natural variation of telomere length in A. thaliana, identifies a network of QTL that influence telomere length homeostasis, examines telomere length dynamics in plants with hybrid backgrounds, and shows the effects of two identified regions on telomere length regulation.
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Affiliation(s)
- Nick Fulcher
- Gregor Mendel Institute, Austrian Academy of Sciences, Vienna Biocenter, Vienna 1030, Austria
| | - Astrid Teubenbacher
- Gregor Mendel Institute, Austrian Academy of Sciences, Vienna Biocenter, Vienna 1030, Austria
| | - Envel Kerdaffrec
- Gregor Mendel Institute, Austrian Academy of Sciences, Vienna Biocenter, Vienna 1030, Austria
| | - Ashley Farlow
- Gregor Mendel Institute, Austrian Academy of Sciences, Vienna Biocenter, Vienna 1030, Austria
| | - Magnus Nordborg
- Gregor Mendel Institute, Austrian Academy of Sciences, Vienna Biocenter, Vienna 1030, Austria
| | - Karel Riha
- Gregor Mendel Institute, Austrian Academy of Sciences, Vienna Biocenter, Vienna 1030, Austria Central European Institute of Technology, Masaryk University, Kamenice 753/5, Brno, Czech Republic
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Churikov D, Charifi F, Simon MN, Géli V. Rad59-facilitated acquisition of Y' elements by short telomeres delays the onset of senescence. PLoS Genet 2014; 10:e1004736. [PMID: 25375789 PMCID: PMC4222662 DOI: 10.1371/journal.pgen.1004736] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2014] [Accepted: 09/05/2014] [Indexed: 12/25/2022] Open
Abstract
Telomerase-negative yeasts survive via one of the two Rad52-dependent recombination pathways, which have distinct genetic requirements. Although the telomere pattern of type I and type II survivors is well characterized, the mechanistic details of short telomere rearrangement into highly evolved pattern observed in survivors are still missing. Here, we analyze immediate events taking place at the abruptly shortened VII-L and native telomeres. We show that short telomeres engage in pairing with internal Rap1-bound TG1–3-like tracts present between subtelomeric X and Y′ elements, which is followed by BIR-mediated non-reciprocal translocation of Y′ element and terminal TG1–3 repeats from the donor end onto the shortened telomere. We found that choice of the Y′ donor was not random, since both engineered telomere VII-L and native VI-R acquired Y′ elements from partially overlapping sets of specific chromosome ends. Although short telomere repair was associated with transient delay in cell divisions, Y′ translocation on native telomeres did not require Mec1-dependent checkpoint. Furthermore, the homeologous pairing between the terminal TG1–3 repeats at VII-L and internal repeats on other chromosome ends was largely independent of Rad51, but instead it was facilitated by Rad59 that stimulates Rad52 strand annealing activity. Therefore, Y′ translocation events taking place during presenescence are genetically separable from Rad51-dependent Y′ amplification process that occurs later during type I survivor formation. We show that Rad59-facilitated Y′ translocations on X-only telomeres delay the onset of senescence while preparing ground for type I survivor formation. In humans, telomerase is expressed in the germline and stem, but is repressed in somatic cells, which limits replicative lifespan of the latter. To unleash cell proliferation, telomerase is reactivated in most human cancers, but some cancer cells employ alternative lengthening of telomeres (ALT) based on homologous recombination (HR) to escape senescence. Recombination-based telomere maintenance similar to ALT was originally discovered in budding yeast deficient in telomerase activity. Two types of telomere arrangement that depend on two genetically distinct HR pathways (RAD51- and RAD59-dependent) were identified in post-senescent survivors, but the transition to telomere maintenance by HR is poorly understood. Here, we show that one of the earliest steps of short telomere rearrangement in telomerase-negative yeast is directly related to the “short telomere rescue pathway” proposed 20 years ago by Lundblad and Blackburn, which culminates in the acquisition of subtelomeric Y′ element by shortened telomere. We found that this telomere rearrangement depends on Rad52 strand annealing activity stimulated by Rad59, thus it is distinct from Rad51-dependent Y′ amplification process observed in type I survivors. We show that continuous repair of critically short telomeres in telomerase-negative cells delays the onset of senescence and prepares the ground for telomere maintenance by HR.
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Affiliation(s)
- Dmitri Churikov
- Marseille Cancer Research Center (CRCM), U1068 Inserm, UMR7258 CNRS, Aix Marseille University, Institut Paoli-Calmettes, LNCC (Equipe labellisée), Marseille, France
| | - Ferose Charifi
- Marseille Cancer Research Center (CRCM), U1068 Inserm, UMR7258 CNRS, Aix Marseille University, Institut Paoli-Calmettes, LNCC (Equipe labellisée), Marseille, France
| | - Marie-Noëlle Simon
- Marseille Cancer Research Center (CRCM), U1068 Inserm, UMR7258 CNRS, Aix Marseille University, Institut Paoli-Calmettes, LNCC (Equipe labellisée), Marseille, France
| | - Vincent Géli
- Marseille Cancer Research Center (CRCM), U1068 Inserm, UMR7258 CNRS, Aix Marseille University, Institut Paoli-Calmettes, LNCC (Equipe labellisée), Marseille, France
- * E-mail:
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Malyavko AN, Parfenova YY, Zvereva MI, Dontsova OA. Telomere length regulation in budding yeasts. FEBS Lett 2014; 588:2530-6. [PMID: 24914478 DOI: 10.1016/j.febslet.2014.05.049] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2014] [Revised: 05/23/2014] [Accepted: 05/23/2014] [Indexed: 11/19/2022]
Abstract
Telomeres are the nucleoprotein caps of chromosomes. Their length must be tightly regulated in order to maintain the stability of the genome. This is achieved by the intricate network of interactions between different proteins and protein-RNA complexes. Different organisms use various mechanisms for telomere length homeostasis. However, details of these mechanisms are not yet completely understood. In this review we have summarized our latest achievements in the understanding of telomere length regulation in budding yeasts.
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Affiliation(s)
- Alexander N Malyavko
- Faculty of Chemistry, Lomonosov Moscow State University, 119999 Moscow, Russia; Belozersky Institute, Moscow State University, Leninskie Gory 1, Bldg. 40, 119991 Moscow, Russia
| | - Yuliya Y Parfenova
- Faculty of Chemistry, Lomonosov Moscow State University, 119999 Moscow, Russia; Belozersky Institute, Moscow State University, Leninskie Gory 1, Bldg. 40, 119991 Moscow, Russia
| | - Maria I Zvereva
- Faculty of Chemistry, Lomonosov Moscow State University, 119999 Moscow, Russia; Belozersky Institute, Moscow State University, Leninskie Gory 1, Bldg. 40, 119991 Moscow, Russia
| | - Olga A Dontsova
- Faculty of Chemistry, Lomonosov Moscow State University, 119999 Moscow, Russia; Belozersky Institute, Moscow State University, Leninskie Gory 1, Bldg. 40, 119991 Moscow, Russia.
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31
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Soudet J, Jolivet P, Teixeira MT. Elucidation of the DNA end-replication problem in Saccharomyces cerevisiae. Mol Cell 2014; 53:954-64. [PMID: 24656131 DOI: 10.1016/j.molcel.2014.02.030] [Citation(s) in RCA: 72] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2013] [Revised: 01/15/2014] [Accepted: 01/31/2014] [Indexed: 11/26/2022]
Abstract
The model for telomere shortening at each replication cycle is currently incomplete, and the exact contribution of the telomeric 3' overhang to the shortening rate remains unclear. Here, we demonstrate key steps of the mechanism of telomere replication in Saccharomyces cerevisiae. By following the dynamics of telomeres during replication at near-nucleotide resolution, we find that the leading-strand synthesis generates blunt-end intermediates before being 5'-resected and filled in. Importantly, the shortening rate is set by positioning the last Okazaki fragments at the very ends of the chromosome. Thus, telomeres shorten in direct proportion to the 3' overhang lengths of 5-10 nucleotides that are present in parental templates. Furthermore, the telomeric protein Cdc13 coordinates leading- and lagging-strand syntheses. Taken together, our data unravel a precise choreography of telomere replication elucidating the DNA end-replication problem and provide a framework to understand the control of the cell proliferation potential.
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Affiliation(s)
- Julien Soudet
- Centre National de la Recherche Scientifique, UMR8226, Laboratoire de Biologie Moléculaire et Cellulaire des Eucaryotes, Institut de Biologie Physico-Chimique, 75005 Paris, France; Sorbonne Universités, UPMC Univ Paris 06, UMR8226, Laboratoire de Biologie Moléculaire et Cellulaire des Eucaryotes, Institut de Biologie Physico-Chimique, 75005 Paris, France
| | - Pascale Jolivet
- Centre National de la Recherche Scientifique, UMR8226, Laboratoire de Biologie Moléculaire et Cellulaire des Eucaryotes, Institut de Biologie Physico-Chimique, 75005 Paris, France; Sorbonne Universités, UPMC Univ Paris 06, UMR8226, Laboratoire de Biologie Moléculaire et Cellulaire des Eucaryotes, Institut de Biologie Physico-Chimique, 75005 Paris, France
| | - Maria Teresa Teixeira
- Centre National de la Recherche Scientifique, UMR8226, Laboratoire de Biologie Moléculaire et Cellulaire des Eucaryotes, Institut de Biologie Physico-Chimique, 75005 Paris, France; Sorbonne Universités, UPMC Univ Paris 06, UMR8226, Laboratoire de Biologie Moléculaire et Cellulaire des Eucaryotes, Institut de Biologie Physico-Chimique, 75005 Paris, France.
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Rubinstein L, Ungar L, Harari Y, Babin V, Ben-Aroya S, Merenyi G, Marjavaara L, Chabes A, Kupiec M. Telomere length kinetics assay (TELKA) sorts the telomere length maintenance (tlm) mutants into functional groups. Nucleic Acids Res 2014; 42:6314-25. [PMID: 24728996 PMCID: PMC4041441 DOI: 10.1093/nar/gku267] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Genome-wide systematic screens in yeast have uncovered a large gene network (the telomere length maintenance network or TLM), encompassing more than 400 genes, which acts coordinatively to maintain telomere length. Identifying the genes was an important first stage; the next challenge is to decipher their mechanism of action and to organize then into functional groups or pathways. Here we present a new telomere-length measuring program, TelQuant, and a novel assay, telomere length kinetics assay, and use them to organize tlm mutants into functional classes. Our results show that a mutant defective for the relatively unknown MET7 gene has the same telomeric kinetics as mutants defective for the ribonucleotide reductase subunit Rnr1, in charge of the limiting step in dNTP synthesis, or for the Ku heterodimer, a well-established telomere complex. We confirm the epistatic relationship between the mutants and show that physical interactions exist between Rnr1 and Met7. We also show that Met7 and the Ku heterodimer affect dNTP formation, and play a role in non-homologous end joining. Thus, our telomere kinetics assay uncovers new functional groups, as well as complex genetic interactions between tlm mutants.
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Affiliation(s)
- Linda Rubinstein
- Department of Molecular Microbiology and Biotechnology, Tel Aviv University, Ramat Aviv 69978, Israel
| | - Lior Ungar
- Department of Molecular Microbiology and Biotechnology, Tel Aviv University, Ramat Aviv 69978, Israel
| | - Yaniv Harari
- Department of Molecular Microbiology and Biotechnology, Tel Aviv University, Ramat Aviv 69978, Israel
| | - Vera Babin
- Department of Molecular Microbiology and Biotechnology, Tel Aviv University, Ramat Aviv 69978, Israel
| | - Shay Ben-Aroya
- Faculty of Life Sciences Bar-Ilan University, Ramat-Gan, Israel
| | - Gabor Merenyi
- Department of Medical Biochemistry and Biophysics and Laboratory for Molecular Infection Medicine Sweden (MIMS), Umeå University, Umeå 901 87, Sweden
| | - Lisette Marjavaara
- Department of Medical Biochemistry and Biophysics and Laboratory for Molecular Infection Medicine Sweden (MIMS), Umeå University, Umeå 901 87, Sweden
| | - Andrei Chabes
- Department of Medical Biochemistry and Biophysics and Laboratory for Molecular Infection Medicine Sweden (MIMS), Umeå University, Umeå 901 87, Sweden
| | - Martin Kupiec
- Department of Molecular Microbiology and Biotechnology, Tel Aviv University, Ramat Aviv 69978, Israel
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Cusanelli E, Chartrand P. Telomeric noncoding RNA: telomeric repeat-containing RNA in telomere biology. WILEY INTERDISCIPLINARY REVIEWS-RNA 2014; 5:407-19. [PMID: 24523222 DOI: 10.1002/wrna.1220] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Telomeres are nucleoprotein structures that cap the ends of eukaryotic chromosomes, protecting them from degradation and activation of DNA damage response. For this reason, functional telomeres are vital to genome stability. For years, telomeres were assumed to be transcriptionally silent, because of their heterochromatic state. It was only recently shown that, in several organisms, telomeres are transcribed, giving rise to a long noncoding RNA (lncRNA) called telomeric repeat-containing RNA (TERRA). Several lines of evidence now indicate that TERRA molecules play crucial roles in telomere homeostasis and telomere functions. Recent studies have shown that the expression and regulation of TERRA are dynamically controlled by each chromosome end. TERRA has been involved in the regulation of telomere length, telomerase activity, and heterochromatin formation at telomeres. The correct regulation of the telomeric transcripts may be essential to genome stability, and altered TERRA levels associate with tumorigenesis and cellular senescence. Thus, the study of the molecular mechanisms of TERRA biogenesis and function may advance the understanding of telomere-related diseases, including cancer and aging.
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Affiliation(s)
- Emilio Cusanelli
- Department of Biochemistry and Molecular Medicine, Université de Montréal, Montréal, Canada
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35
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Gao H, Moss DL, Parke C, Tatum D, Lustig AJ. The Ctf18RFC clamp loader is essential for telomere stability in telomerase-negative and mre11 mutant alleles. PLoS One 2014; 9:e88633. [PMID: 24533124 PMCID: PMC3923045 DOI: 10.1371/journal.pone.0088633] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2013] [Accepted: 01/13/2014] [Indexed: 11/19/2022] Open
Abstract
The function of the replication clamp loaders in the semi-conservative telomere replication and their relationship to telomerase- and recombination mechanisms of telomere addition remains ambiguous. We have investigated the variant clamp loader Ctf18 RFC (Replication Factor C). To understand the role of Ctf18 at the telomere, we first investigated genetic interactions after loss of Ctf18 and TLC1 (the yeast telomerase RNA). We find that the tlc1Δ ctf18Δ double mutant confers a rapid >1000-fold decrease in viability. The rate of loss was similar to the kinetics of cell death in rad52Δ tlc1Δ cells. However, the Ctf18 pathway is distinct from Rad52, required for the repair of DSBs, as demonstrated by the synthetic lethality of rad52▵ tlc1Δ ctf18Δ triple mutants. These data suggest that each mutant elicits non-redundant defects acting on the same substrate. Second, interactions of the yeast hyper-recombinational mutant, mre11A470T, with ctf18▵ confer a synergistic cold sensitivity. The phenotype of these double mutants ultimately results in telomere loss and the generation of recombinational survivors. We observed a similar synergism between single mutants that led to hypersensitivity to the DNA alkylating agent, methane methyl sulphonate (MMS), the replication fork inhibitor hydroxyurea (HU), and to a failure to separate telomeres of sister chromatids. Hence, ctf18Δ and mre11A470T act in different pathways on telomere substrates for multiple phenotypes. The mre11A470T cells also displayed a DNA damage response (DDR) at 15°C but not at 30°C while ctf18Δ mutants conferred a constitutive DDR activity. Both the 15°C DDR pattern and growth rate were reversible at 30°C and displayed telomerase activity in vivo. We hypothesize that Ctf18 confers protection against stalling and/or breaks at the replication fork in cells that either lack, or are compromised for, telomerase activity. This Ctf18-based function is likely to contribute another level to telomere size homeostasis.
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Affiliation(s)
- Honghai Gao
- Department of Biochemistry and Molecular Biology, Tulane University Medical Center, New Orleans, Louisiana, United States of America
| | - Daniel L. Moss
- Department of Biochemistry and Molecular Biology, Tulane University Medical Center, New Orleans, Louisiana, United States of America
| | - Courtney Parke
- Department of Biochemistry and Molecular Biology, Tulane University Medical Center, New Orleans, Louisiana, United States of America
| | - Danielle Tatum
- Department of Biochemistry and Molecular Biology, Tulane University Medical Center, New Orleans, Louisiana, United States of America
| | - Arthur J. Lustig
- Department of Biochemistry and Molecular Biology, Tulane University Medical Center, New Orleans, Louisiana, United States of America
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36
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Fallet E, Jolivet P, Soudet J, Lisby M, Gilson E, Teixeira MT. Length-dependent processing of telomeres in the absence of telomerase. Nucleic Acids Res 2014; 42:3648-65. [PMID: 24393774 PMCID: PMC3973311 DOI: 10.1093/nar/gkt1328] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
In the absence of telomerase, telomeres progressively shorten with every round of DNA replication, leading to replicative senescence. In telomerase-deficient Saccharomyces cerevisiae, the shortest telomere triggers the onset of senescence by activating the DNA damage checkpoint and recruiting homologous recombination (HR) factors. Yet, the molecular structures that trigger this checkpoint and the mechanisms of repair have remained elusive. By tracking individual telomeres, we show that telomeres are subjected to different pathways depending on their length. We first demonstrate a progressive accumulation of subtelomeric single-stranded DNA (ssDNA) through 5'-3' resection as telomeres shorten. Thus, exposure of subtelomeric ssDNA could be the signal for cell cycle arrest in senescence. Strikingly, early after loss of telomerase, HR counteracts subtelomeric ssDNA accumulation rather than elongates telomeres. We then asked whether replication repair pathways contribute to this mechanism. We uncovered that Rad5, a DNA helicase/Ubiquitin ligase of the error-free branch of the DNA damage tolerance (DDT) pathway, associates with native telomeres and cooperates with HR in senescent cells. We propose that DDT acts in a length-independent manner, whereas an HR-based repair using the sister chromatid as a template buffers precocious 5'-3' resection at the shortest telomeres.
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Affiliation(s)
- Emilie Fallet
- Laboratoire de Biologie Moléculaire et Cellulaire des Eucaryotes, Institut de Biologie Physico-Chimique, Centre National de la Recherche Scientifique, Université Pierre et Marie Curie, FRE3354, 75005 Paris, France, Laboratoire de Biologie Moléculaire de la Cellule, Centre National de la Recherche Scientifique, Ecole Normale Supérieure de Lyon, Université de Lyon 1, UMR5239, 69364 Lyon Cedex 07, France, Department of Biology, University of Copenhagen, Ole Maaløes Vej 5, DK-2200 Copenhagen N, Denmark, Institute for Research on Cancer and Aging, Nice (IRCAN), University of Nice Sophia-Antipolis, CNRS UMR7284/INSERM U1081, Faculty of Medicine, Nice F-06107, France and Department of Medical Genetics, CHU Nice, 06202 Nice cedex 3, France
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Abstract
Telomeres are the physical ends of eukaryotic linear chromosomes. Telomeres form special structures that cap chromosome ends to prevent degradation by nucleolytic attack and to distinguish chromosome termini from DNA double-strand breaks. With few exceptions, telomeres are composed primarily of repetitive DNA associated with proteins that interact specifically with double- or single-stranded telomeric DNA or with each other, forming highly ordered and dynamic complexes involved in telomere maintenance and length regulation. In proliferative cells and unicellular organisms, telomeric DNA is replicated by the actions of telomerase, a specialized reverse transcriptase. In the absence of telomerase, some cells employ a recombination-based DNA replication pathway known as alternative lengthening of telomeres. However, mammalian somatic cells that naturally lack telomerase activity show telomere shortening with increasing age leading to cell cycle arrest and senescence. In another way, mutations or deletions of telomerase components can lead to inherited genetic disorders, and the depletion of telomeric proteins can elicit the action of distinct kinases-dependent DNA damage response, culminating in chromosomal abnormalities that are incompatible with life. In addition to the intricate network formed by the interrelationships among telomeric proteins, long noncoding RNAs that arise from subtelomeric regions, named telomeric repeat-containing RNA, are also implicated in telomerase regulation and telomere maintenance. The goal for the next years is to increase our knowledge about the mechanisms that regulate telomere homeostasis and the means by which their absence or defect can elicit telomere dysfunction, which generally results in gross genomic instability and genetic diseases.
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Telomeric noncoding RNA TERRA is induced by telomere shortening to nucleate telomerase molecules at short telomeres. Mol Cell 2013; 51:780-91. [PMID: 24074956 DOI: 10.1016/j.molcel.2013.08.029] [Citation(s) in RCA: 164] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2013] [Revised: 07/05/2013] [Accepted: 08/19/2013] [Indexed: 11/20/2022]
Abstract
Elongation of a short telomere depends on the action of multiple telomerase molecules, which are visible as telomerase RNA foci or clusters associated with telomeres in yeast and mammalian cells. How several telomerase molecules act on a single short telomere is unknown. Herein, we report that the telomeric noncoding RNA TERRA is involved in the nucleation of telomerase molecules into clusters prior to their recruitment at a short telomere. We find that telomere shortening induces TERRA expression, leading to the accumulation of TERRA molecules into a nuclear focus. Simultaneous time-lapse imaging of telomerase RNA and TERRA reveals spontaneous events of telomerase nucleation on TERRA foci in early S phase, generating TERRA-telomerase clusters. This cluster is subsequently recruited to the short telomere from which TERRA transcripts originate during S phase. We propose that telomere shortening induces noncoding RNA expression to coordinate the recruitment and activity of telomerase molecules at short telomeres.
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Bonetti D, Martina M, Falcettoni M, Longhese MP. Telomere-end processing: mechanisms and regulation. Chromosoma 2013; 123:57-66. [PMID: 24122006 DOI: 10.1007/s00412-013-0440-y] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2013] [Revised: 10/04/2013] [Accepted: 10/04/2013] [Indexed: 10/26/2022]
Abstract
Telomeres are specialized nucleoprotein complexes that provide protection to the ends of eukaryotic chromosomes. Telomeric DNA consists of tandemly repeated G-rich sequences that terminate with a 3' single-stranded overhang, which is important for telomere extension by the telomerase enzyme. This structure, as well as most of the proteins that specifically bind double and single-stranded telomeric DNA, are conserved from yeast to humans, suggesting that the mechanisms underlying telomere identity are based on common principles. The telomeric 3' overhang is generated by different events depending on whether the newly synthesized strand is the product of leading- or lagging-strand synthesis. Here, we review the mechanisms that regulate these processes at Saccharomyces cerevisiae and mammalian telomeres.
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Affiliation(s)
- Diego Bonetti
- Dipartimento di Biotecnologie e Bioscienze, Università di Milano-Bicocca, Piazza della Scienza 2, 20126, Milan, Italy
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40
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Abstract
The absence of telomerase in many eukaryotes leads to the gradual shortening of telomeres, causing replicative senescence. In humans, this proliferation barrier constitutes a tumor suppressor mechanism and may be involved in cellular aging. Yet the heterogeneity of the senescence phenotype has hindered the understanding of its onset. Here we investigated the regulation of telomere length and its control of senescence heterogeneity. Because the length of the shortest telomeres can potentially regulate cell fate, we focus on their dynamics in Saccharomyces cerevisiae. We developed a stochastic model of telomere dynamics built on the protein-counting model, where an increasing number of protein-bound telomeric repeats shift telomeres into a nonextendable state by telomerase. Using numerical simulations, we found that the length of the shortest telomere is well separated from the length of the others, suggesting a prominent role in triggering senescence. We evaluated this possibility using classical genetic analyses of tetrads, combined with a quantitative and sensitive assay for senescence. In contrast to mitosis of telomerase-negative cells, which produces two cells with identical senescence onset, meiosis is able to segregate a determinant of senescence onset among the telomerase-negative spores. The frequency of such segregation is in accordance with this determinant being the length of the shortest telomere. Taken together, our results substantiate the length of the shortest telomere as being the key genetic marker determining senescence onset in S. cerevisiae.
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Pfeiffer V, Lingner J. Replication of telomeres and the regulation of telomerase. Cold Spring Harb Perspect Biol 2013; 5:a010405. [PMID: 23543032 DOI: 10.1101/cshperspect.a010405] [Citation(s) in RCA: 85] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Telomeres are the physical ends of eukaryotic chromosomes. They protect chromosome ends from DNA degradation, recombination, and DNA end fusions, and they are important for nuclear architecture. Telomeres provide a mechanism for their replication by semiconservative DNA replication and length maintenance by telomerase. Through telomerase repression and induced telomere shortening, telomeres provide the means to regulate cellular life span. In this review, we introduce the current knowledge on telomere composition and structure. We then discuss in depth the current understanding of how telomere components mediate their function during semiconservative DNA replication and how telomerase is regulated at the end of the chromosome. We focus our discussion on the telomeres from mammals and the yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe.
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Affiliation(s)
- Verena Pfeiffer
- Swiss Institute for Experimental Cancer Research (ISREC), School of Life Sciences, Frontiers in Genetics National Center of Competence in Research, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland
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42
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Abstract
The mechanisms that maintain the stability of chromosome ends have broad impact on genome integrity in all eukaryotes. Budding yeast is a premier organism for telomere studies. Many fundamental concepts of telomere and telomerase function were first established in yeast and then extended to other organisms. We present a comprehensive review of yeast telomere biology that covers capping, replication, recombination, and transcription. We think of it as yeast telomeres—soup to nuts.
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Abstract
Most human cells lack telomerase, the enzyme that elongates telomeres. The resulting telomere erosion eventually limits cell proliferation and tissue renewal, thereby impacting age-dependent pathologies. In this issue of Genes & Development, a technical tour-de-force by Chow and colleagues (pp. 1167-1178) reveals a highly choreographed sequence of events that processes newly replicated chromosome ends into mature telomeres. This sheds new light on an underappreciated contribution to telomere dynamics that may be as important as telomerase in dictating the correlation between life span and telomere length.
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Affiliation(s)
- Victoria Lundblad
- Salk Institute for Biological Studies, La Jolla, California 92037, USA.
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44
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Pfeiffer V, Lingner J. TERRA promotes telomere shortening through exonuclease 1-mediated resection of chromosome ends. PLoS Genet 2012; 8:e1002747. [PMID: 22719262 PMCID: PMC3375253 DOI: 10.1371/journal.pgen.1002747] [Citation(s) in RCA: 110] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2012] [Accepted: 04/18/2012] [Indexed: 01/30/2023] Open
Abstract
The long noncoding telomeric repeat containing RNA (TERRA) is expressed at chromosome ends. TERRA upregulation upon experimental manipulation or in ICF (immunodeficiency, centromeric instability, facial anomalies) patients correlates with short telomeres. To study the mechanism of telomere length control by TERRA in Saccharomyces cerevisiae, we mapped the transcriptional start site of TERRA at telomere 1L and inserted a doxycycline regulatable promoter upstream. Induction of TERRA transcription led to telomere shortening of 1L but not of other chromosome ends. TERRA interacts with the Exo1-inhibiting Ku70/80 complex, and deletion of EXO1 but not MRE11 fully suppressed the TERRA–mediated short telomere phenotype in presence and absence of telomerase. Thus TERRA transcription facilitates the 5′-3′ nuclease activity of Exo1 at chromosome ends, providing a means to regulate the telomere shortening rate. Thereby, telomere transcription can regulate cellular lifespan through modulation of chromosome end processing activities. Telomeres protect chromosome ends from end fusion and end degradation, and they regulate cellular lifespan. Telomerase, a reverse transcriptase, maintains telomere length. The end replication problem and the processing of DNA ends by nucleases cause telomere shortening. Telomeres are transcribed into a long noncoding RNA known as TERRA. ICF syndrome derived patient cells have short telomeres and enriched TERRA. TERRA inhibits telomerase activity in vitro. To analyze TERRA function in vivo, we used the model organism Saccharomyces cerevisiae. We identified the natural TERRA promoter at one chromosome end and replaced it with an artificial promoter to modulate TERRA transcription with a drug. TERRA induction leads to telomere shortening at this specific chromosome end. We show that telomere shortening is a consequence of increased activation of the 5′-3′ Exonuclease 1 at the transcribed telomere with no notable effects on telomerase recruitment and activity. The Ku protein controls Exonuclease 1 activity at chromosome ends. TERRA physically and genetically interacts with Ku and appears to interfere with its ability to inhibit Exonuclease 1. Thus, we demonstrate how TERRA expression controls telomere length through the regulation of the processing of chromosome ends. Therefore, telomere transcription can regulate cellular lifespan independently of telomerase.
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Affiliation(s)
| | - Joachim Lingner
- Swiss Institute for Experimental Cancer Research (ISREC), School of Life Sciences, Frontiers in Genetics National Center of Competence in Research, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
- * E-mail:
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Chow TT, Zhao Y, Mak SS, Shay JW, Wright WE. Early and late steps in telomere overhang processing in normal human cells: the position of the final RNA primer drives telomere shortening. Genes Dev 2012; 26:1167-78. [PMID: 22661228 PMCID: PMC3371406 DOI: 10.1101/gad.187211.112] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2012] [Accepted: 04/19/2012] [Indexed: 11/24/2022]
Abstract
Telomere overhangs are essential for telomere end protection and telomerase extension, but how telomere overhangs are generated is unknown. Leading daughter strands synthesized by conventional semiconservation DNA replication are initially blunt, while lagging daughter strands are shorter by at least the size of the final RNA primer, which is thought to be located at extreme chromosome ends. We developed a variety of new approaches to define the steps in the processing of these overhangs. We show that the final lagging RNA primer is not terminal but is randomly positioned ~70-100 nucleotides from the ends and is not removed for more than an hour. This identifies an important intrinsic step in replicative aging. Telomeric termini are processed in two distinct phases. During the early phase, which occupies 1-2 h following replication of the duplex telomeric DNA, several steps occur on both leading and lagging daughters. Leading telomere processing remains incomplete until late S/G2, when the C-terminal nucleotide is specified-referred to as the late phase. These observations suggest the presence of previously unsuspected complexes and signaling events required for the replication of the ends of human chromosomes.
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Affiliation(s)
- Tracy T. Chow
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
| | - Yong Zhao
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
| | - Sabrina S. Mak
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
| | - Jerry W. Shay
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
| | - Woodring E. Wright
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
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46
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Maicher A, Kastner L, Dees M, Luke B. Deregulated telomere transcription causes replication-dependent telomere shortening and promotes cellular senescence. Nucleic Acids Res 2012; 40:6649-59. [PMID: 22553368 PMCID: PMC3413150 DOI: 10.1093/nar/gks358] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Telomeres are transcribed into non-coding TElomeric Repeat containing RNAs (TERRA). We have employed a transcriptionally inducible telomere to investigate how telomere transcription affects telomere function in Saccharomyces cerevisiae. We report that telomere shortening resulting from high levels of telomere transcription stems from a DNA replication-dependent loss of telomere tracts, which can occur independent of both telomerase inhibition and homologous recombination. We show that in order for telomere loss to occur, transcription must pass through the telomere tract itself producing a TERRA molecule. We demonstrate that increased telomere transcription of a single telomere leads to a premature cellular senescence in the absence of a telomere maintenance mechanism (telomerase and homology directed repair). Similar rapid senescence and telomere shortening are also seen in sir2Δ cells with compromised telomere maintenance, where TERRA levels are increased at natural telomeres. These data suggest that telomere transcription must be tightly controlled to prevent telomere loss and early onset senescence.
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Affiliation(s)
- André Maicher
- Zentrum für Molekulare Biologie der Universität Heidelberg, DKFZ-ZMBH Allianz, Im Neuenheimer Feld 282, 69120 Heidelberg, Germany
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47
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Live cell imaging of telomerase RNA dynamics reveals cell cycle-dependent clustering of telomerase at elongating telomeres. Mol Cell 2012; 44:819-27. [PMID: 22152484 DOI: 10.1016/j.molcel.2011.09.020] [Citation(s) in RCA: 98] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2011] [Revised: 06/21/2011] [Accepted: 09/12/2011] [Indexed: 11/22/2022]
Abstract
The telomerase, which is composed of both protein and RNA, maintains genome stability by replenishing telomeric repeats at the ends of chromosomes. Here, we use live-cell imaging to follow yeast telomerase RNA dynamics and recruitment to telomeres in single cells. Tracking of single telomerase particles revealed a diffusive behavior and transient association with telomeres in G1 and G2 phases of the cell cycle. Interestingly, concurrent with telomere elongation in late S phase, a subset of telomerase enzyme clusters and stably associates with few telomeres. Our data show that this clustering represents elongating telomerase and it depends on regulators of telomerase at telomeres (MRX, Tel1, Rif1/2, and Cdc13). Furthermore, the assay revealed premature telomere elongation in G1 in a rif1/2 strains, suggesting that Rif1/2 act as cell-cycle dependent negative regulators of telomerase. We propose that telomere elongation is organized around a local and transient accumulation of several telomerases on a few telomeres.
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A balance between Tel1 and Rif2 activities regulates nucleolytic processing and elongation at telomeres. Mol Cell Biol 2012; 32:1604-17. [PMID: 22354991 DOI: 10.1128/mcb.06547-11] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Generation of G-strand overhangs at Saccharomyces cerevisiae yeast telomeres depends primarily on the MRX (Mre11-Rad50-Xrs2) complex, which is also necessary to maintain telomere length by recruiting the Tel1 kinase. MRX physically interacts with Rif2, which inhibits both resection and elongation of telomeres. We provide evidence that regulation of telomere processing and elongation relies on a balance between Tel1 and Rif2 activities. Tel1 regulates telomere nucleolytic processing by promoting MRX activity. In fact, the lack of Tel1 impairs MRX-dependent telomere resection, which is instead enhanced by the Tel1-hy909 mutant variant, which causes telomerase-dependent telomere overelongation. The Tel1-hy909 variant is more robustly associated than wild-type Tel1 to double-strand-break (DSB) ends carrying telomeric repeat sequences. Furthermore, it increases the persistence at a DSB adjacent to telomeric repeats of both MRX and Est1, which in turn likely account for the increased telomere resection and elongation in TEL1-hy909 cells. Strikingly, Rif2 is unable to negatively regulate processing and lengthening at TEL1-hy909 telomeres, indicating that the Tel1-hy909 variant overcomes the inhibitory activity exerted by Rif2 on MRX. Altogether, these findings highlight a primary role of Tel1 in overcoming Rif2-dependent negative regulation of MRX activity in telomere resection and elongation.
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Becerra SC, Thambugala HT, Erickson AR, Lee CK, Lewis LK. Reversibility of replicative senescence in Saccharomyces cerevisiae: effect of homologous recombination and cell cycle checkpoints. DNA Repair (Amst) 2011; 11:35-45. [PMID: 22071150 DOI: 10.1016/j.dnarep.2011.10.003] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2011] [Revised: 10/01/2011] [Accepted: 10/04/2011] [Indexed: 12/13/2022]
Abstract
Primary human somatic cells grown in culture divide a finite number of times, exhibiting progressive changes in metabolism and morphology before cessation of cycling. This telomere-initiated cellular senescence occurs because cells have halted production of telomerase, a DNA polymerase required for stabilization of chromosome ends. Telomerase-deficient Saccharomyces cerevisiae cells undergo a similar process, with most cells arresting growth after approximately 60 generations. In the current study we demonstrate that senescence is largely reversible. Reactivation of telomerase (EST2) expression in the growth-arrested cells led to resumption of cycling and reversal of senescent cell characteristics. Rescue was also observed after mating of senescent haploid cells with telomerase-proficient cells to form stable diploids. Although senescence was reversible in DNA damage checkpoint response mutants (mec3 and/or rad24 cells), survival of recombination-defective rad52 mutants remained low after telomerase reactivation. Telomere lengths in rescued est2 cells were initially half those of wildtype cells, but could be restored to normal by propagation for ∼70 generations in the presence of telomerase. These results place limitations on possible models for senescence and indicate that most cells, despite gross morphological changes and short, resected telomeres, do not experience lethal DNA damage and become irreversibly committed to death.
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Affiliation(s)
- Sandra C Becerra
- Department of Chemistry and Biochemistry, Texas State University, San Marcos, TX 78666, USA
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50
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Abstract
Telomeres are nucleoprotein structures that protect the ends of human chromosomes through the formation of a 'cap', thus preventing exonucleolytic degradation, inter- and intra-chromosomal fusion, and subsequent chromosomal instability. During aging, telomere shortening correlates with tissue dysfunction and loss of renewal capacity. In human cancer, telomere dysfunction is involved in early chromosome instability, long-term cellular proliferation, and possibly other processes related to cell survival and microenvironment. Telomeres constitute an attractive target for the development of novel small-molecule anti-cancer drugs. In particular, individual protein components of the core telomere higher-order chromatin structure (known as the telosome or 'shelterin' complex) are promising candidate targets for cancer therapy.
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