1
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Nageshan RK, Ortega R, Krogan N, Cooper JP. Fate of telomere entanglements is dictated by the timing of anaphase midregion nuclear envelope breakdown. Nat Commun 2024; 15:4707. [PMID: 38830842 PMCID: PMC11148042 DOI: 10.1038/s41467-024-48382-2] [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: 01/21/2024] [Accepted: 04/29/2024] [Indexed: 06/05/2024] Open
Abstract
Persisting replication intermediates can confer mitotic catastrophe. Loss of the fission yeast telomere protein Taz1 (ortholog of mammalian TRF1/TRF2) causes telomeric replication fork (RF) stalling and consequently, telomere entanglements that stretch between segregating mitotic chromosomes. At ≤20 °C, these entanglements fail to resolve, resulting in lethality. Rif1, a conserved DNA replication/repair protein, hinders the resolution of telomere entanglements without affecting their formation. At mitosis, local nuclear envelope (NE) breakdown occurs in the cell's midregion. Here we demonstrate that entanglement resolution occurs in the cytoplasm following this NE breakdown. However, in response to taz1Δ telomeric entanglements, Rif1 delays midregion NE breakdown at ≤20 °C, in turn disfavoring entanglement resolution. Moreover, Rif1 overexpression in an otherwise wild-type setting causes cold-specific NE defects and lethality, which are rescued by membrane fluidization. Hence, NE properties confer the cold-specificity of taz1Δ lethality, which stems from postponement of NE breakdown. We propose that such postponement promotes clearance of simple stalled RFs, but resolution of complex entanglements (involving strand invasion between nonsister telomeres) requires rapid exposure to the cytoplasm.
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Affiliation(s)
- Rishi Kumar Nageshan
- Department of Biochemistry and Molecular Genetics, University of Colorado Anschutz Medical Campus, Aurora, CO, 80045, USA.
| | - Raquel Ortega
- Department of Molecular Cellular and Developmental Biology, University of Colorado, Boulder, CO, USA
| | - Nevan Krogan
- Quantitative Biosciences Institute (QBI), University of California, San Francisco, CA, 94158, USA
- Department of Cellular and Molecular Pharmacology, University of California, San Francisco, CA, 94158, USA
- Gladstone Institute of Data Science and Biotechnology, J. David Gladstone Institutes, San Francisco, CA, 94158, USA
| | - Julia Promisel Cooper
- Department of Biochemistry and Molecular Genetics, University of Colorado Anschutz Medical Campus, Aurora, CO, 80045, USA.
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2
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Kuse R, Ishii K. Flexible Attachment and Detachment of Centromeres and Telomeres to and from Chromosomes. Biomolecules 2023; 13:1016. [PMID: 37371596 DOI: 10.3390/biom13061016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2023] [Revised: 06/15/2023] [Accepted: 06/18/2023] [Indexed: 06/29/2023] Open
Abstract
Accurate transmission of genomic information across multiple cell divisions and generations, without any losses or errors, is fundamental to all living organisms. To achieve this goal, eukaryotes devised chromosomes. Eukaryotic genomes are represented by multiple linear chromosomes in the nucleus, each carrying a centromere in the middle, a telomere at both ends, and multiple origins of replication along the chromosome arms. Although all three of these DNA elements are indispensable for chromosome function, centromeres and telomeres possess the potential to detach from the original chromosome and attach to new chromosomal positions, as evident from the events of telomere fusion, centromere inactivation, telomere healing, and neocentromere formation. These events seem to occur spontaneously in nature but have not yet been elucidated clearly, because they are relatively infrequent and sometimes detrimental. To address this issue, experimental setups have been developed using model organisms such as yeast. In this article, we review some of the key experiments that provide clues as to the extent to which these paradoxical and elusive features of chromosomally indispensable elements may become valuable in the natural context.
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Affiliation(s)
- Riku Kuse
- Laboratory of Chromosome Function and Regulation, Graduate School of Engineering, Kochi University of Technology, Kochi 782-8502, Japan
| | - Kojiro Ishii
- Laboratory of Chromosome Function and Regulation, Graduate School of Engineering, Kochi University of Technology, Kochi 782-8502, Japan
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3
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Hill HJ, Bonser D, Golic KG. Dicentric chromosome breakage in Drosophila melanogaster is influenced by pericentric heterochromatin and occurs in nonconserved hotspots. Genetics 2023; 224:iyad052. [PMID: 37010100 PMCID: PMC10213500 DOI: 10.1093/genetics/iyad052] [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: 10/18/2022] [Revised: 10/18/2022] [Accepted: 03/13/2023] [Indexed: 04/04/2023] Open
Abstract
Chromosome breakage plays an important role in the evolution of karyotypes and can produce deleterious effects within a single individual, such as aneuploidy or cancer. Forces that influence how and where chromosomes break are not fully understood. In humans, breakage tends to occur in conserved hotspots called common fragile sites (CFS), especially during replication stress. By following the fate of dicentric chromosomes in Drosophila melanogaster, we find that breakage under tension also tends to occur in specific hotspots. Our experimental approach was to induce sister chromatid exchange in a ring chromosome to generate a dicentric chromosome with a double chromatid bridge. In the following cell division, the dicentric bridges may break. We analyzed the breakage patterns of 3 different ring-X chromosomes. These chromosomes differ by the amount and quality of heterochromatin they carry as well as their genealogical history. For all 3 chromosomes, breakage occurs preferentially in several hotspots. Surprisingly, we found that the hotspot locations are not conserved between the 3 chromosomes: each displays a unique array of breakage hotspots. The lack of hotspot conservation, along with a lack of response to aphidicolin, suggests that these breakage sites are not entirely analogous to CFS and may reveal new mechanisms of chromosome fragility. Additionally, the frequency of dicentric breakage and the durability of each chromosome's spindle attachment vary significantly between the 3 chromosomes and are correlated with the origin of the centromere and the amount of pericentric heterochromatin. We suggest that different centromere strengths could account for this.
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Affiliation(s)
- Hunter J Hill
- School of Biological Sciences, University of Utah, Salt Lake City, UT 84112, USA
| | - Danielle Bonser
- School of Biological Sciences, University of Utah, Salt Lake City, UT 84112, USA
| | - Kent G Golic
- School of Biological Sciences, University of Utah, Salt Lake City, UT 84112, USA
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4
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Takeuchi C, Yokoshi M, Kondo S, Shibuya A, Saito K, Fukaya T, Siomi H, Iwasaki Y. Mod(mdg4) variants repress telomeric retrotransposon HeT-A by blocking subtelomeric enhancers. Nucleic Acids Res 2022; 50:11580-11599. [PMID: 36373634 PMCID: PMC9723646 DOI: 10.1093/nar/gkac1034] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2022] [Revised: 10/17/2022] [Accepted: 10/22/2022] [Indexed: 11/16/2022] Open
Abstract
Telomeres in Drosophila are composed of sequential non-LTR retrotransposons HeT-A, TART and TAHRE. Although they are repressed by the PIWI-piRNA pathway or heterochromatin in the germline, the regulation of these retrotransposons in somatic cells is poorly understood. In this study, we demonstrated that specific splice variants of Mod(mdg4) repress HeT-A by blocking subtelomeric enhancers in ovarian somatic cells. Among the variants, we found that the Mod(mdg4)-N variant represses HeT-A expression the most efficiently. Subtelomeric sequences bound by Mod(mdg4)-N block enhancer activity within subtelomeric TAS-R repeats. This enhancer-blocking activity is increased by the tandem association of Mod(mdg4)-N to repetitive subtelomeric sequences. In addition, the association of Mod(mdg4)-N couples with the recruitment of RNA polymerase II to the subtelomeres, which reinforces its enhancer-blocking function. Our findings provide novel insights into how telomeric retrotransposons are regulated by the specific variants of insulator proteins associated with subtelomeric sequences.
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Affiliation(s)
- Chikara Takeuchi
- Department of Molecular Biology, Keio University School of Medicine, Tokyo 160-8582, Japan
| | - Moe Yokoshi
- Laboratory of Transcription Dynamics, Research Center for Biological Visualization, Institute for Quantitative Biosciences, The University of Tokyo, Tokyo 113-0032, Japan
| | - Shu Kondo
- Department of Chromosome Science, National Institute of Genetics, Research Organization of Information and Systems (ROIS), Shizuoka 411-8540, Japan
| | - Aoi Shibuya
- Department of Molecular Biology, Keio University School of Medicine, Tokyo 160-8582, Japan
| | - Kuniaki Saito
- Department of Chromosome Science, National Institute of Genetics, Research Organization of Information and Systems (ROIS), Shizuoka 411-8540, Japan
| | - Takashi Fukaya
- Laboratory of Transcription Dynamics, Research Center for Biological Visualization, Institute for Quantitative Biosciences, The University of Tokyo, Tokyo 113-0032, Japan,Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, Tokyo 113-0032, Japan
| | | | - Yuka W Iwasaki
- To whom correspondence should be addressed. Tel: +81 3 5363 3529; Fax: +81 3 5363 3266;
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5
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Vaurs M, Audry J, Runge KW, Géli V, Coulon S. A proto-telomere is elongated by telomerase in a shelterin-dependent manner in quiescent fission yeast cells. Nucleic Acids Res 2022; 50:11682-11695. [PMID: 36330920 PMCID: PMC9723628 DOI: 10.1093/nar/gkac986] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2022] [Revised: 10/08/2022] [Accepted: 10/17/2022] [Indexed: 11/06/2022] Open
Abstract
Telomere elongation is coupled with genome replication, raising the question of the repair of short telomeres in post-mitotic cells. We investigated the fate of a telomere-repeat capped end that mimics a single short telomere in quiescent fission yeast cells. We show that telomerase is able to elongate this single short telomere during quiescence despite the binding of Ku to the proto-telomere. While Taz1 and Rap1 repress telomerase in vegetative cells, both shelterin proteins are required for efficient telomere extension in quiescent cells, underscoring a distinct mode of telomerase control. We further show that Rad3ATR and Tel1ATM are redundantly required for telomere elongation in quiescence through the phosphorylation of Ccq1 and that Rif1 and its associated-PP1 phosphatases negatively regulate telomerase activity by opposing Ccq1 phosphorylation. The distinct mode of telomerase regulation in quiescent fission yeast cells may be relevant to that in human stem and progenitor cells.
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Affiliation(s)
- Mélina Vaurs
- CNRS, INSERM, Aix Marseille Univ, Institut Paoli-Calmettes, CRCM, Equipe labellisée par la Ligue Nationale contre le Cancer, Marseille, F-13009, France
| | - Julien Audry
- Department of Inflammation and Immunity, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, OH, USA
| | - Kurt W Runge
- Department of Inflammation and Immunity, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, OH, USA,Department of Genetics and Genome Sciences, Case Western Reserve University, Cleveland, OH, USA
| | - Vincent Géli
- Correspondence may also be addressed to Vincent Géli.
| | - Stéphane Coulon
- To whom correspondence should be addressed. Tel: +33 4 86 97 74 07; Fax: +33 4 86 97 74 99;
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6
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Pan L, Tormey D, Bobon N, Baumann P. Rap1 prevents fusions between long telomeres in fission yeast. EMBO J 2022; 41:e110458. [PMID: 36059259 PMCID: PMC9574727 DOI: 10.15252/embj.2021110458] [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: 12/15/2021] [Revised: 08/04/2022] [Accepted: 08/08/2022] [Indexed: 11/15/2022] Open
Abstract
The conserved Rap1 protein is part of the shelterin complex that plays critical roles in chromosome end protection and telomere length regulation. Previous studies have addressed how fission yeast Rap1 contributes to telomere length maintenance, but the mechanism by which the protein inhibits end fusions has remained elusive. Here, we use a mutagenesis screen in combination with high‐throughput sequencing to identify several amino acid positions in Rap1 that have key roles in end protection. Interestingly, mutations at these sites render cells susceptible to genome instability in a conditional manner, whereby longer telomeres are prone to undergoing end fusions, while telomeres within the normal length range are sufficiently protected. The protection of long telomeres is in part dependent on their nuclear envelope attachment mediated by the Rap1–Bqt4 interaction. Our data demonstrate that long telomeres represent a challenge for the maintenance of genome integrity, thereby providing an explanation for species‐specific upper limits on telomere length.
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Affiliation(s)
- Lili Pan
- Department of Biology, Johannes Gutenberg University, Mainz, Germany
| | - Duncan Tormey
- Stowers Institute for Medical Research, Kansas City, MO, USA
| | - Nadine Bobon
- Department of Biology, Johannes Gutenberg University, Mainz, Germany
| | - Peter Baumann
- Department of Biology, Johannes Gutenberg University, Mainz, Germany.,Institute of Molecular Biology, Mainz, Germany
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7
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Wang L, Wu B, Ma Y, Ren Z, Li W. The blooming of an old story on the bouquet. Biol Reprod 2022; 107:289-300. [PMID: 35470849 DOI: 10.1093/biolre/ioac075] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2021] [Revised: 03/09/2022] [Accepted: 04/12/2022] [Indexed: 11/13/2022] Open
Abstract
As an evolutionarily conserved process, the bouquet stage during meiosis was discovered over a century ago, and active research on this important stage continues. Since the discovery of the first bouquet-related protein Taz1p in 1998, several bouquet formation-related proteins have been identified in various eukaryotes. These proteins are involved in the interaction between telomeres and the inner nuclear membrane (INM), and once these interactions are disrupted, meiotic progression is arrested, leading to infertility. Recent studies have provided significant insights into the relationships and interactions among bouquet formation-related proteins. In this review, we summarize the components involved in telomere-INM interactions and focus on their roles in bouquet formation and telomere homeostasis maintenance. In addition, we examined bouquet-related proteins in different species from an evolutionary viewpoint, highlighting the potential interactions among them.
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Affiliation(s)
- Lina Wang
- State Key Laboratory of Stem Cell and Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, China.,Department of Respiratory, China National Clinical Research Center of Respiratory Diseases, Beijing Children's Hospital, Capital Medical University, National Center for Children's Health, Beijing 100045, China.,University of the Chinese Academy of Sciences, Beijing 100049, China
| | - Bingbing Wu
- State Key Laboratory of Stem Cell and Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, China.,University of the Chinese Academy of Sciences, Beijing 100049, China
| | - Yanjie Ma
- State Key Laboratory of Stem Cell and Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, China.,University of the Chinese Academy of Sciences, Beijing 100049, China
| | - Zhengxing Ren
- State Key Laboratory of Stem Cell and Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, China.,University of the Chinese Academy of Sciences, Beijing 100049, China
| | - Wei Li
- State Key Laboratory of Stem Cell and Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, China.,University of the Chinese Academy of Sciences, Beijing 100049, China.,Institute of Reproductive Health and Perinatology, Guangzhou Women and Children's Medical Center, Guangzhou Medical University, 510623 Guangzhou, China
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8
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Apte MS, Masuda H, Wheeler DL, Cooper JP. RNAi and Ino80 complex control rate limiting translocation step that moves rDNA to eroding telomeres. Nucleic Acids Res 2021; 49:8161-8176. [PMID: 34244792 PMCID: PMC8373062 DOI: 10.1093/nar/gkab586] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2021] [Revised: 06/18/2021] [Accepted: 07/01/2021] [Indexed: 01/21/2023] Open
Abstract
The discovery of HAATIrDNA, a telomerase-negative survival mode in which canonical telomeres are replaced with ribosomal DNA (rDNA) repeats that acquire chromosome end-protection capability, raised crucial questions as to how rDNA tracts 'jump' to eroding chromosome ends. Here, we show that HAATIrDNA formation is initiated and limited by a single translocation that juxtaposes rDNA from Chromosome (Chr) III onto subtelomeric elements (STE) on Chr I or II; this rare reaction requires RNAi and the Ino80 nucleosome remodeling complex (Ino80C), thus defining an unforeseen relationship between these two machineries. The unique STE-rDNA junction created by this initial translocation is efficiently copied to the remaining STE chromosome ends, independently of RNAi or Ino80C. Intriguingly, both RNAi and Ino80C machineries contain a component that plays dual roles in HAATI subtype choice. Dcr1 of the RNAi pathway and Iec1 of Ino80C both promote HAATIrDNA formation as part of their respective canonical machineries, but both also inhibit formation of the exceedingly rare HAATISTE (where STE sequences mobilize throughout the genome and assume chromosome end protection capacity) in non-canonical, pathway-independent manners. This work provides a glimpse into a previously unrecognized crosstalk between RNAi and Ino80C in controlling unusual translocation reactions that establish telomere-free linear chromosome ends.
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Affiliation(s)
- Manasi S Apte
- Laboratory of Biochemistry and Molecular Biology, NCI, NIH, Bethesda, MD 20892, USA
| | - Hirohisa Masuda
- Department of Biochemistry and Molecular Genetics, University of Colorado Anschutz Medical Campus, Aurora, CO 80045, USA
| | - David Lee Wheeler
- Laboratory of Biochemistry and Molecular Biology, NCI, NIH, Bethesda, MD 20892, USA
| | - Julia Promisel Cooper
- Department of Biochemistry and Molecular Genetics, University of Colorado Anschutz Medical Campus, Aurora, CO 80045, USA
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9
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Li B. Keeping Balance Between Genetic Stability and Plasticity at the Telomere and Subtelomere of Trypanosoma brucei. Front Cell Dev Biol 2021; 9:699639. [PMID: 34291053 PMCID: PMC8287324 DOI: 10.3389/fcell.2021.699639] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2021] [Accepted: 06/08/2021] [Indexed: 12/13/2022] Open
Abstract
Telomeres, the nucleoprotein complexes at chromosome ends, are well-known for their essential roles in genome integrity and chromosome stability. Yet, telomeres and subtelomeres are frequently less stable than chromosome internal regions. Many subtelomeric genes are important for responding to environmental cues, and subtelomeric instability can facilitate organismal adaptation to extracellular changes, which is a common theme in a number of microbial pathogens. In this review, I will focus on the delicate and important balance between stability and plasticity at telomeres and subtelomeres of a kinetoplastid parasite, Trypanosoma brucei, which causes human African trypanosomiasis and undergoes antigenic variation to evade the host immune response. I will summarize the current understanding about T. brucei telomere protein complex, the telomeric transcript, and telomeric R-loops, focusing on their roles in maintaining telomere and subtelomere stability and integrity. The similarities and differences in functions and underlying mechanisms of T. brucei telomere factors will be compared with those in human and yeast cells.
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Affiliation(s)
- Bibo Li
- Center for Gene Regulation in Health and Disease, Department of Biological, Geological, and Environmental Sciences, College of Sciences and Health Professions, Cleveland State University, Cleveland, OH, United States.,Case Comprehensive Cancer Center, Case Western Reserve University, Cleveland, OH, United States.,Department of Inflammation and Immunity, Lerner Research Institute, Cleveland Clinic, Cleveland, OH, United States.,Center for RNA Science and Therapeutics, Case Western Reserve University, Cleveland, OH, United States
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10
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Jones CE, Forsburg SL. Monitoring Schizosaccharomyces pombe genome stress by visualizing end-binding protein Ku. Biol Open 2021; 10:bio.054346. [PMID: 33579693 PMCID: PMC7904001 DOI: 10.1242/bio.054346] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Studies of genome stability have exploited visualization of fluorescently tagged proteins in live cells to characterize DNA damage, checkpoint, and repair responses. In this report, we describe a new tool for fission yeast, a tagged version of the end-binding protein Pku70 which is part of the KU protein complex. We compare Pku70 localization to other markers upon treatment to various genotoxins, and identify a unique pattern of distribution. Pku70 provides a new tool to define and characterize DNA lesions and the repair response. Summary: The authors describe a fluorescently tagged Ku70 protein to monitor replication stress in live S. pombe cells.
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Affiliation(s)
- Chance E Jones
- Program in Molecular & Computational Biology, University of Southern California, Los Angeles, CA 90089, USA
| | - Susan L Forsburg
- Program in Molecular & Computational Biology, University of Southern California, Los Angeles, CA 90089, USA
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11
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Hu Y, Bennett HW, Liu N, Moravec M, Williams JF, Azzalin CM, King MC. RNA-DNA Hybrids Support Recombination-Based Telomere Maintenance in Fission Yeast. Genetics 2019; 213:431-447. [PMID: 31405990 PMCID: PMC6781888 DOI: 10.1534/genetics.119.302606] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2019] [Accepted: 08/09/2019] [Indexed: 11/18/2022] Open
Abstract
A subset of cancers rely on telomerase-independent mechanisms to maintain their chromosome ends. The predominant "alternative lengthening of telomeres" pathway appears dependent on homology-directed repair (HDR) to maintain telomeric DNA. However, the molecular changes needed for cells to productively engage in telomeric HDR are poorly understood. To gain new insights into this transition, we monitored the state of telomeres during serial culture of fission yeast (Schizosaccharomyces pombe) lacking the telomerase recruitment factor Ccq1. Rad52 is loaded onto critically short telomeres shortly after germination despite continued telomere erosion, suggesting that recruitment of recombination factors is not sufficient to maintain telomeres in the absence of telomerase function. Instead, survivor formation coincides with the derepression of telomeric repeat-containing RNA (TERRA). In this context, degradation of TERRA associated with the telomere in the form of R-loops drives a severe growth crisis, ultimately leading to a novel type of survivor with linear chromosomes and altered cytological telomere characteristics, including the loss of the shelterin component Rap1 (but not the TRF1/TRF2 ortholog, Taz1) from the telomere. We demonstrate that deletion of Rap1 is protective in this context, preventing the growth crisis that is otherwise triggered by degradation of telomeric R-loops in survivors with linear chromosomes. These findings suggest that upregulation of telomere-engaged TERRA, or altered recruitment of shelterin components, can support telomerase-independent telomere maintenance.
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Affiliation(s)
- Yan Hu
- Department of Cell Biology, Yale School of Medicine, New Haven, Connecticut 06520-8002
| | - Henrietta W Bennett
- Department of Cell Biology, Yale School of Medicine, New Haven, Connecticut 06520-8002
| | - Na Liu
- Department of Cell Biology, Yale School of Medicine, New Haven, Connecticut 06520-8002
| | - Martin Moravec
- Institute of Biochemistry (IBC), Eidgenössische Technische Hochschule Zürich (ETHZ), 8093, Switzerland
| | - Jessica F Williams
- Department of Cell Biology, Yale School of Medicine, New Haven, Connecticut 06520-8002
| | - Claus M Azzalin
- Instituto de Medicina Molecular João Lobo Antunes (iMM), Faculdade de Medicina da Universidade de Lisboa, 1649-028, Portugal
| | - Megan C King
- Department of Cell Biology, Yale School of Medicine, New Haven, Connecticut 06520-8002
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12
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Irie H, Yamamoto I, Tarumoto Y, Tashiro S, Runge KW, Ishikawa F. Telomere-binding proteins Taz1 and Rap1 regulate DSB repair and suppress gross chromosomal rearrangements in fission yeast. PLoS Genet 2019; 15:e1008335. [PMID: 31454352 PMCID: PMC6733473 DOI: 10.1371/journal.pgen.1008335] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2019] [Revised: 09/09/2019] [Accepted: 07/28/2019] [Indexed: 11/19/2022] Open
Abstract
Genomic rearrangements (gross chromosomal rearrangements, GCRs) threatens genome integrity and cause cell death or tumor formation. At the terminus of linear chromosomes, a telomere-binding protein complex, called shelterin, ensures chromosome stability by preventing chromosome end-to-end fusions and regulating telomere length homeostasis. As such, shelterin-mediated telomere functions play a pivotal role in suppressing GCR formation. However, it remains unclear whether the shelterin proteins play any direct role in inhibiting GCR at non-telomeric regions. Here, we have established a GCR assay for the first time in fission yeast and measured GCR rates in various mutants. We found that fission yeast cells lacking shelterin components Taz1 or Rap1 (mammalian TRF1/2 or RAP1 homologues, respectively) showed higher GCR rates compared to wild-type, accumulating large chromosome deletions. Genetic dissection of Rap1 revealed that Rap1 contributes to inhibiting GCRs via two independent pathways. The N-terminal BRCT-domain promotes faithful DSB repair, as determined by I-SceI-mediated DSB-induction experiments; moreover, association with Poz1 mediated by the central Poz1-binding domain regulates telomerase accessibility to DSBs, leading to suppression of de novo telomere additions. Our data highlight unappreciated functions of the shelterin components Taz1 and Rap1 in maintaining genome stability, specifically by preventing non-telomeric GCRs.
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Affiliation(s)
- Hiroyuki Irie
- Department of Gene Mechanisms, Graduate School of Biostudies, Kyoto University, Sakyo-ku, Kyoto, Japan
| | - Io Yamamoto
- Department of Gene Mechanisms, Graduate School of Biostudies, Kyoto University, Sakyo-ku, Kyoto, Japan
| | - Yusuke Tarumoto
- Department of Gene Mechanisms, Graduate School of Biostudies, Kyoto University, Sakyo-ku, Kyoto, Japan
| | - Sanki Tashiro
- Department of Gene Mechanisms, Graduate School of Biostudies, Kyoto University, Sakyo-ku, Kyoto, Japan
| | - Kurt W. Runge
- Department of Molecular Genetics, Cleveland Clinic Lerner College of Medicine, Cleveland, Ohio, United States of America
| | - Fuyuki Ishikawa
- Department of Gene Mechanisms, Graduate School of Biostudies, Kyoto University, Sakyo-ku, Kyoto, Japan
- * E-mail:
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13
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Telomere DNA length-dependent regulation of DNA replication timing at internal late replication origins. Sci Rep 2019; 9:9946. [PMID: 31289327 PMCID: PMC6617677 DOI: 10.1038/s41598-019-46229-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2019] [Accepted: 06/20/2019] [Indexed: 02/07/2023] Open
Abstract
DNA replication is initiated at replication origins on chromosomes at their scheduled time during S phase of the cell cycle. Replication timing control is highly conserved among eukaryotes but the underlying mechanisms are not fully understood. Recent studies have revealed that some telomere-binding proteins regulate replication timing at late-replicating origins throughout the genome. To investigate the molecular basis of this process, we analyzed the effects of excessive elongation of telomere DNA on replication timing by deleting telomere-associated shelterin proteins in Schizosaccharomyces pombe. We found that rap1∆ and poz1∆ cells showed abnormally accelerated replication at internal late origins but not at subtelomere regions. These defects were suppressed by removal of telomere DNA and by deletion of the telomere-binding protein Taz1. Furthermore, Sds21—a counter protein phosphatase against Dbf4-dependent kinase (DDK)—accumulated at elongated telomeres in a Taz1-dependent manner but was depleted at internal late origins, indicating that highly elongated telomeres sequester Sds21 at telomeres and perturb replication timing at internal regions. These results demonstrate that telomere DNA length is an important determinant of replication timing at internal regions of chromosomes in eukaryotes.
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14
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Greenwood J, Patel H, Cech TR, Cooper JP. Fission yeast telosomes: non-canonical histone-containing chromatin structures dependent on shelterin and RNA. Nucleic Acids Res 2018; 46:8865-8875. [PMID: 29992245 PMCID: PMC6158490 DOI: 10.1093/nar/gky605] [Citation(s) in RCA: 7] [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: 03/02/2018] [Revised: 05/25/2018] [Accepted: 06/25/2018] [Indexed: 12/16/2022] Open
Abstract
Despite the prime importance of telomeres in chromosome stability, significant mysteries surround the architecture of telomeric chromatin. Through micrococcal nuclease mapping, we show that fission yeast chromosome ends are assembled into distinct protected structures ('telosomes') encompassing the telomeric DNA repeats and over half a kilobase of subtelomeric DNA. Telosome formation depends on the conserved telomeric proteins Taz1 and Rap1, and surprisingly, RNA. Although yeast telomeres have long been thought to be free of histones, we show that this is not the case; telomere repeats contain histones. While telomeric histone H3 bears the heterochromatic lys9-methyl mark, we show that this mark is dispensable for telosome formation. Therefore, telomeric chromatin is organized at an architectural level, in which telomere-binding proteins and RNAs impose a unique nucleosome arrangement, and a second level, in which histone modifications are superimposed upon the higher order architecture.
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Affiliation(s)
- Jessica Greenwood
- Telomere Biology Laboratory, Cancer Research UK, London Research Institute, London, WC2A 3LY, UK
- Cell Cycle Lab, The Francis Crick Institute, 1 Midland Road, London NW1 1AT, UK
| | - Harshil Patel
- Bioinformatics and Biostatistics, The Francis Crick Institute, 1 Midland Road, London NW1 1AT, UK
| | - Thomas R Cech
- Howard Hughes Medical Institute, Department of Chemistry and Biochemistry, BioFrontiers Institute, University of Colorado, Boulder, CO 80309, USA
| | - Julia Promisel Cooper
- Telomere Biology Laboratory, Cancer Research UK, London Research Institute, London, WC2A 3LY, UK
- Howard Hughes Medical Institute, Department of Chemistry and Biochemistry, BioFrontiers Institute, University of Colorado, Boulder, CO 80309, USA
- Telomere Biology Section, Laboratory of Biochemistry and Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
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15
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Armstrong CA, Tomita K. Fundamental mechanisms of telomerase action in yeasts and mammals: understanding telomeres and telomerase in cancer cells. Open Biol 2018; 7:rsob.160338. [PMID: 28330934 PMCID: PMC5376709 DOI: 10.1098/rsob.160338] [Citation(s) in RCA: 49] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2016] [Accepted: 02/20/2017] [Indexed: 12/12/2022] Open
Abstract
Aberrant activation of telomerase occurs in 85–90% of all cancers and underpins the ability of cancer cells to bypass their proliferative limit, rendering them immortal. The activity of telomerase is tightly controlled at multiple levels, from transcriptional regulation of the telomerase components to holoenzyme biogenesis and recruitment to the telomere, and finally activation and processivity. However, studies using cancer cell lines and other model systems have begun to reveal features of telomeres and telomerase that are unique to cancer. This review summarizes our current knowledge on the mechanisms of telomerase recruitment and activation using insights from studies in mammals and budding and fission yeasts. Finally, we discuss the differences in telomere homeostasis between normal cells and cancer cells, which may provide a foundation for telomere/telomerase targeted cancer treatments.
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Affiliation(s)
- Christine A Armstrong
- Chromosome Maintenance Group, UCL Cancer Institute, University College London, 72 Huntley Street, London WC1E 6DD, UK
| | - Kazunori Tomita
- Chromosome Maintenance Group, UCL Cancer Institute, University College London, 72 Huntley Street, London WC1E 6DD, UK
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16
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Begnis M, Apte MS, Masuda H, Jain D, Wheeler DL, Cooper JP. RNAi drives nonreciprocal translocations at eroding chromosome ends to establish telomere-free linear chromosomes. Genes Dev 2018; 32:537-554. [PMID: 29654060 PMCID: PMC5959237 DOI: 10.1101/gad.311712.118] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2018] [Accepted: 03/29/2018] [Indexed: 12/19/2022]
Abstract
In this study, Begnis et al. show that HAATI, which is a mode of telomerase-minus survival in which canonical telomeres are superseded by blocks of nontelomeric rDNA heterochromatin that have spread to all chromosome ends, is formed and maintained. Their findings demonstrate that HAATI arises when telomere loss triggers a newly recognized illegitimate recombination pathway that requires RNAi factors, uncovering novel roles for ncRNAs in assembling a telomere-free chromosome end protection device. The identification of telomerase-negative HAATI (heterochromatin amplification-mediated and telomerase-independent) cells, in which telomeres are superseded by nontelomeric heterochromatin tracts, challenged the idea that canonical telomeres are essential for chromosome linearity and raised crucial questions as to how such tracts translocate to eroding chromosome ends and confer end protection. Here we show that HAATI arises when telomere loss triggers a newly recognized illegitimate translocation pathway that requires RNAi factors. While RNAi is necessary for the translocation events that mobilize ribosomal DNA (rDNA) tracts to all chromosome ends (forming “HAATIrDNA” chromosomes), it is dispensable for HAATIrDNA maintenance. Surprisingly, Dicer (Dcr1) plays a separate, RNAi-independent role in preventing formation of the rare HAATI subtype in which a different repetitive element (the subtelomeric element) replaces telomeres. Using genetics and fusions between shelterin components and rDNA-binding proteins, we mapped the mechanism by which rDNA loci engage crucial end protection factors—despite the absence of telomere repeats—and secure end protection. Sequence analysis of HAATIrDNA genomes allowed us to propose RNA and DNA polymerase template-switching models for the mechanism of RNAi-triggered rDNA translocations. Collectively, our results reveal unforeseen roles for noncoding RNAs (ncRNAs) in assembling a telomere-free chromosome end protection device.
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Affiliation(s)
- Martina Begnis
- Telomere Biology Section, Laboratory of Biochemistry and Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.,Telomere Biology Laboratory, Cancer Research UK, London Research Institute, London WC2A 3LY, United Kingdom
| | - Manasi S Apte
- Telomere Biology Section, Laboratory of Biochemistry and Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA
| | - Hirohisa Masuda
- Telomere Biology Section, Laboratory of Biochemistry and Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA
| | - Devanshi Jain
- Molecular Biology Program, Memorial Sloan Kettering Cancer Center, New York, New York 10065, USA
| | - David Lee Wheeler
- Laboratory of Biochemistry and Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA
| | - Julia Promisel Cooper
- Telomere Biology Section, Laboratory of Biochemistry and Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.,Telomere Biology Laboratory, Cancer Research UK, London Research Institute, London WC2A 3LY, United Kingdom
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17
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Stewart JA, Wang Y, Ackerson SM, Schuck PL. Emerging roles of CST in maintaining genome stability and human disease. Front Biosci (Landmark Ed) 2018; 23:1564-1586. [PMID: 29293451 DOI: 10.2741/4661] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
The human CTC1-STN1-TEN1 (CST) complex is a single-stranded DNA binding protein that shares homology with RPA and interacts with DNA polymerase alpha/primase. CST complexes are conserved from yeasts to humans and function in telomere maintenance. A common role of CST across species is in the regulation of telomere extension by telomerase and C-strand fill-in synthesis. However, recent studies also indicate that CST promotes telomere duplex replication as well the rescue of stalled DNA replication at non-telomeric sites. Furthermore, CST dysfunction and mutation is associated with several genetic diseases and cancers. In this review, we will summarize what is known about CST with a particular focus on the emerging roles of CST in DNA replication and human disease.
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Affiliation(s)
- Jason A Stewart
- Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, USA,
| | - Yilin Wang
- Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, USA
| | - Stephanie M Ackerson
- Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, USA
| | - Percy Logan Schuck
- Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, USA
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18
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Hou H, Cooper JP. Stretching, scrambling, piercing and entangling: Challenges for telomeres in mitotic and meiotic chromosome segregation. Differentiation 2018; 100:12-20. [PMID: 29413748 DOI: 10.1016/j.diff.2018.01.002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2017] [Revised: 01/21/2018] [Accepted: 01/23/2018] [Indexed: 12/24/2022]
Abstract
The consequences of telomere loss or dysfunction become most prominent when cells enter the nuclear division stage of the cell cycle. At this climactic stage when chromosome segregation occurs, telomere fusions or entanglements can lead to chromosome breakage, wreaking havoc on genome stability. Here we review recent progress in understanding the mechanisms of detangling and breaking telomere associations at mitosis, as well as the unique ways in which telomeres are processed to allow regulated sister telomere separation. Moreover, we discuss unexpected roles for telomeres in orchestrating nuclear envelope breakdown and spindle formation, crucial processes for nuclear division. Finally, we discuss the discovery that telomeres create microdomains in the nucleus that are conducive to centromere assembly, cementing the unexpectedly influential role of telomeres in mitosis.
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Affiliation(s)
- Haitong Hou
- Telomere Biology Section, LBMB, NCI, NIH, Building 37, Room 6050, Bethesda MD 20892, USA
| | - Julia Promisel Cooper
- Telomere Biology Section, LBMB, NCI, NIH, Building 37, Room 6050, Bethesda MD 20892, USA.
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19
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Shelterin components mediate genome reorganization in response to replication stress. Proc Natl Acad Sci U S A 2017; 114:5479-5484. [PMID: 28490498 DOI: 10.1073/pnas.1705527114] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
The dynamic nature of genome organization impacts critical nuclear functions including the regulation of gene expression, replication, and DNA damage repair. Despite significant progress, the mechanisms responsible for reorganization of the genome in response to cellular stress, such as aberrant DNA replication, are poorly understood. Here, we show that fission yeast cells carrying a mutation in the DNA-binding protein Sap1 show defects in DNA replication progression and genome stability and display extensive changes in genome organization. Chromosomal regions such as subtelomeres that show defects in replication progression associate with the nuclear envelope in sap1 mutant cells. Moreover, high-resolution, genome-wide chromosome conformation capture (Hi-C) analysis revealed prominent contacts between telomeres and chromosomal arm regions containing replication origins proximal to binding sites for Taz1, a component of the Shelterin telomere protection complex. Strikingly, we find that Shelterin components are required for interactions between Taz1-associated chromosomal arm regions and telomeres. These analyses reveal an unexpected role for Shelterin components in genome reorganization in cells experiencing replication stress, with important implications for understanding the mechanisms governing replication and genome stability.
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20
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Nonhomologous End-Joining with Minimal Sequence Loss Is Promoted by the Mre11-Rad50-Nbs1-Ctp1 Complex in Schizosaccharomyces pombe. Genetics 2017; 206:481-496. [PMID: 28292918 DOI: 10.1534/genetics.117.200972] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2017] [Accepted: 02/24/2017] [Indexed: 11/18/2022] Open
Abstract
While the Mre11-Rad50-Nbs1 (MRN) complex has known roles in repair processes like homologous recombination and microhomology-mediated end-joining, its role in nonhomologous end-joining (NHEJ) is unclear as Saccharomyces cerevisiae, Schizosaccharomyces pombe, and mammals have different requirements for repairing cut DNA ends. Most double-strand breaks (DSBs) require nucleolytic processing prior to DNA ligation. Therefore, we studied repair using the Hermes transposon, whose excision leaves a DSB capped by hairpin ends similar to structures generated by palindromes and trinucleotide repeats. We generated single Hermes insertions using a novel S. pombe transient transfection system, and used Hermes excision to show a requirement for MRN in the NHEJ of nonligatable ends. NHEJ repair was indicated by the >1000-fold decrease in excision in cells lacking Ku or DNA ligase 4. Most repaired excision sites had <5 bp of sequence loss or mutation, characteristic for NHEJ and similar excision events in metazoans, and in contrast to the more extensive loss seen in S. cerevisiaeS. pombe NHEJ was reduced >1000-fold in cells lacking each MRN subunit, and loss of MRN-associated Ctp1 caused a 30-fold reduction. An Mre11 dimer is thought to hold DNA ends together for repair, and Mre11 dimerization domain mutations reduced repair 300-fold. In contrast, a mre11 mutant defective in endonucleolytic activity, the same mutant lacking Ctp1, or the triple mutant also lacking the putative hairpin nuclease Pso2 showed wild-type levels of repair. Thus, MRN may act to recruit the hairpin opening activity that allows subsequent repair.
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21
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Braun S, Barrales RR. Beyond Tethering and the LEM domain: MSCellaneous functions of the inner nuclear membrane Lem2. Nucleus 2016; 7:523-531. [PMID: 27797637 DOI: 10.1080/19491034.2016.1252892] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
The nuclear envelope plays a pivotal role in the functional organization of chromatin. Various inner nuclear membrane (INM) proteins associate with transcriptionally repressed chromatin, which is often found at the nuclear periphery. A prominent example is the conserved family of LEM (LAP2-Emerin-MAN1) domain proteins that interact with DNA-binding proteins and have been proposed to mediate tethering of chromatin to the nuclear membrane. We recently reported that the fission yeast protein Lem2, a homolog of metazoan LEM proteins, contributes to perinuclear localization and silencing of heterochromatin. 1 We demonstrate that binding and tethering of centromeric chromatin depends on the LEM domain of Lem2. Unexpectedly, this domain is dispensable for heterochromatin silencing, which is instead mediated by a different structural domain of Lem2, the MSC (MAN1-Src1 C-terminal) domain. Hence, silencing and tethering by Lem2 can be mechanistically separated. Notably, the MSC domain has multiple functions beyond heterochromatic silencing. Here we discuss the implications of these novel findings for the understanding of this conserved INM protein.
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Affiliation(s)
- Sigurd Braun
- a Department of Physiological Chemistry , Biomedical Center (BMC), Ludwig-Maximilians-University of Munich , Martinsried , Germany
| | - Ramón Ramos Barrales
- a Department of Physiological Chemistry , Biomedical Center (BMC), Ludwig-Maximilians-University of Munich , Martinsried , Germany.,b Present address: Centro Andaluz de Biología del Desarrollo. Universidad Pablo de Olavide, Sevilla-CSIC-Junta de Andalucía , Sevilla , Spain
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22
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Ohno Y, Ogiyama Y, Kubota Y, Kubo T, Ishii K. Acentric chromosome ends are prone to fusion with functional chromosome ends through a homology-directed rearrangement. Nucleic Acids Res 2015; 44:232-44. [PMID: 26433224 PMCID: PMC4705696 DOI: 10.1093/nar/gkv997] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2015] [Accepted: 09/23/2015] [Indexed: 01/19/2023] Open
Abstract
The centromeres of many eukaryotic chromosomes are established epigenetically on potentially variable tandem repeats; hence, these chromosomes are at risk of being acentric. We reported previously that artificially created acentric chromosomes in the fission yeast Schizosaccharomyces pombe can be rescued by end-to-end fusion with functional chromosomes. Here, we show that most acentric/functional chromosome fusion events in S. pombe cells harbouring an acentric chromosome I differed from the non-homologous end-joining-mediated rearrangements that result in deleterious dicentric fusions in normal cells, and were elicited by a previously unidentified homologous recombination (HR) event between chromosome end-associated sequences. The subtelomere repeats associated with the non-fusogenic ends were also destabilized in the surviving cells, suggesting a causal link between general subtelomere destabilization and acentric/functional chromosome fusion. A mutational analysis indicated that a non-canonical HR pathway was involved in the rearrangement. These findings are indicative of a latent mechanism that conditionally induces general subtelomere instability, presumably in the face of accidental centromere loss events, resulting in rescue of the fatal acentric chromosomes by interchromosomal HR.
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Affiliation(s)
- Yuko Ohno
- Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka 565-0871, Japan
| | - Yuki Ogiyama
- Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka 565-0871, Japan
| | - Yoshino Kubota
- Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka 565-0871, Japan
| | - Takuya Kubo
- Graduate School of Environmental Science, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan
| | - Kojiro Ishii
- Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka 565-0871, Japan Institute for Academic Initiatives, Osaka University, Suita, Osaka 565-0871, Japan
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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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Reyes C, Serrurier C, Gauthier T, Gachet Y, Tournier S. Aurora B prevents chromosome arm separation defects by promoting telomere dispersion and disjunction. ACTA ACUST UNITED AC 2015; 208:713-27. [PMID: 25778919 PMCID: PMC4362453 DOI: 10.1083/jcb.201407016] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The segregation of centromeres and telomeres at mitosis is coordinated at multiple levels to prevent the formation of aneuploid cells, a phenotype frequently observed in cancer. Mitotic instability arises from chromosome segregation defects, giving rise to chromatin bridges at anaphase. Most of these defects are corrected before anaphase onset by a mechanism involving Aurora B kinase, a key regulator of mitosis in a wide range of organisms. Here, we describe a new role for Aurora B in telomere dispersion and disjunction during fission yeast mitosis. Telomere dispersion initiates in metaphase, whereas disjunction takes place in anaphase. Dispersion is promoted by the dissociation of Swi6/HP1 and cohesin Rad21 from telomeres, whereas disjunction occurs at anaphase after the phosphorylation of condensin subunit Cnd2. Strikingly, we demonstrate that deletion of Ccq1, a telomeric shelterin component, rescued cell death after Aurora inhibition by promoting the loading of condensin on chromosome arms. Our findings reveal an essential role for telomeres in chromosome arm segregation.
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Affiliation(s)
- Céline Reyes
- Laboratoire de biologie cellulaire et moléculaire du contrôle de la prolifération, Université de Toulouse, F-31062 Toulouse, France Centre National de la Recherche Scientifique, LBCMCP-UMR5088, F-31062 Toulouse, France
| | - Céline Serrurier
- Laboratoire de biologie cellulaire et moléculaire du contrôle de la prolifération, Université de Toulouse, F-31062 Toulouse, France Centre National de la Recherche Scientifique, LBCMCP-UMR5088, F-31062 Toulouse, France
| | - Tiphaine Gauthier
- Laboratoire de biologie cellulaire et moléculaire du contrôle de la prolifération, Université de Toulouse, F-31062 Toulouse, France Centre National de la Recherche Scientifique, LBCMCP-UMR5088, F-31062 Toulouse, France
| | - Yannick Gachet
- Laboratoire de biologie cellulaire et moléculaire du contrôle de la prolifération, Université de Toulouse, F-31062 Toulouse, France Centre National de la Recherche Scientifique, LBCMCP-UMR5088, F-31062 Toulouse, France
| | - Sylvie Tournier
- Laboratoire de biologie cellulaire et moléculaire du contrôle de la prolifération, Université de Toulouse, F-31062 Toulouse, France Centre National de la Recherche Scientifique, LBCMCP-UMR5088, F-31062 Toulouse, France
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25
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Lorenzi LE, Bah A, Wischnewski H, Shchepachev V, Soneson C, Santagostino M, Azzalin CM. Fission yeast Cactin restricts telomere transcription and elongation by controlling Rap1 levels. EMBO J 2014; 34:115-29. [PMID: 25398909 DOI: 10.15252/embj.201489559] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
The telomeric transcriptome comprises multiple long non-coding RNAs generated by transcription of linear chromosome ends. In a screening performed in Schizosaccharomyces pombe, we identified factors modulating the cellular levels of the telomeric transcriptome. Among these factors, Cay1 is the fission yeast member of the conserved family of Cactins, uncharacterized proteins crucial for cell growth and survival. In cay1∆ mutants, the cellular levels of the telomeric factor Rap1 are drastically diminished due to defects in rap1+ pre-mRNA splicing and Rap1 protein stability. cay1∆ cells accumulate histone H3 acetylated at lysine 9 at telomeres, which become transcriptionally desilenced, are over-elongated by telomerase and cause chromosomal aberrations in the cold. Overexpressing Rap1 in cay1+ deleted cells significantly reverts all telomeric defects. Additionally, cay1∆ mutants accumulate unprocessed Tf2 retrotransposon RNA through Rap1-independent mechanisms. Thus, Cay1 plays crucial roles in cells by ultimately harmonizing expression of transcripts originating from seemingly unrelated genomic loci.
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Affiliation(s)
- Luca E Lorenzi
- Institute of Biochemistry (IBC) Eidgenössische Technische Hochschule Zürich (ETHZ), Zürich, Switzerland
| | - Amadou Bah
- Institute of Biochemistry (IBC) Eidgenössische Technische Hochschule Zürich (ETHZ), Zürich, Switzerland
| | - Harry Wischnewski
- Institute of Biochemistry (IBC) Eidgenössische Technische Hochschule Zürich (ETHZ), Zürich, Switzerland
| | - Vadim Shchepachev
- Institute of Biochemistry (IBC) Eidgenössische Technische Hochschule Zürich (ETHZ), Zürich, Switzerland
| | - Charlotte Soneson
- Bioinformatics Core Facility, SIB Swiss Institute of Bioinformatics, Lausanne, Switzerland
| | - Marco Santagostino
- Dipartimento di Biologia e Biotecnologie "L. Spallanzani", Università degli Studi di Pavia, Pavia, Italy
| | - Claus M Azzalin
- Institute of Biochemistry (IBC) Eidgenössische Technische Hochschule Zürich (ETHZ), Zürich, Switzerland
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26
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Marcand S. How do telomeres and NHEJ coexist? Mol Cell Oncol 2014; 1:e963438. [PMID: 27308342 PMCID: PMC4904885 DOI: 10.4161/23723548.2014.963438] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2014] [Revised: 08/01/2014] [Accepted: 08/07/2014] [Indexed: 12/21/2022]
Abstract
The telomeres of eukaryotes are stable open double-strand ends that coexist with nonhomologous end joining (NHEJ), the repair pathway that directly ligates DNA ends generated by double-strand breaks. Since a single end-joining event between 2 telomeres generates a circular chromosome or an unstable dicentric chromosome, NHEJ must be prevented from acting on telomeres. Multiple mechanisms mediated by telomere factors act in synergy to achieve this inhibition.
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Affiliation(s)
- Stéphane Marcand
- CEA; DSV/IRCM/SIGRR/LTR; Fontenay-aux-roses; France; INSERM UMR 967; Fontenay-aux-roses; France
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27
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Rossiello F, Herbig U, Longhese MP, Fumagalli M, d'Adda di Fagagna F. Irreparable telomeric DNA damage and persistent DDR signalling as a shared causative mechanism of cellular senescence and ageing. Curr Opin Genet Dev 2014; 26:89-95. [PMID: 25104620 PMCID: PMC4217147 DOI: 10.1016/j.gde.2014.06.009] [Citation(s) in RCA: 93] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2013] [Revised: 06/22/2014] [Accepted: 06/25/2014] [Indexed: 12/13/2022]
Abstract
The DNA damage response (DDR) orchestrates DNA repair and halts cell cycle. If damage is not resolved, cells can enter into an irreversible state of proliferative arrest called cellular senescence. Organismal ageing in mammals is associated with accumulation of markers of cellular senescence and DDR persistence at telomeres. Since the vast majority of the cells in mammals are non-proliferating, how do they age? Are telomeres involved? Also oncogene activation causes cellular senescence due to altered DNA replication and DDR activation in particular at the telomeres. Is there a common mechanism shared among apparently distinct types of cellular senescence? And what is the role of telomeric DNA damage?
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Affiliation(s)
- Francesca Rossiello
- IFOM Foundation - FIRC Institute of Molecular Oncology Foundation, Milan 20139, Italy
| | - Utz Herbig
- Department of Microbiology and Molecular Genetics, New Jersey Medical School - Cancer Center, Rutgers Biomedical and Health Sciences, Rutgers University, Newark, NJ 07103, USA
| | - Maria Pia Longhese
- Dipartimento di Biotecnologie e Bioscienze, Università di Milano-Bicocca, Milan 20126, Italy
| | - Marzia Fumagalli
- IFOM Foundation - FIRC Institute of Molecular Oncology Foundation, Milan 20139, Italy
| | - Fabrizio d'Adda di Fagagna
- IFOM Foundation - FIRC Institute of Molecular Oncology Foundation, Milan 20139, Italy; Istituto di Genetica Molecolare, Consiglio Nazionale delle Ricerche, Pavia 27100, Italy.
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28
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Chang YT, Moser BA, Nakamura TM. Fission yeast shelterin regulates DNA polymerases and Rad3(ATR) kinase to limit telomere extension. PLoS Genet 2013; 9:e1003936. [PMID: 24244195 PMCID: PMC3820796 DOI: 10.1371/journal.pgen.1003936] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2013] [Accepted: 09/17/2013] [Indexed: 11/19/2022] Open
Abstract
Studies in fission yeast have previously identified evolutionarily conserved shelterin and Stn1-Ten1 complexes, and established Rad3ATR/Tel1ATM-dependent phosphorylation of the shelterin subunit Ccq1 at Thr93 as the critical post-translational modification for telomerase recruitment to telomeres. Furthermore, shelterin subunits Poz1, Rap1 and Taz1 have been identified as negative regulators of Thr93 phosphorylation and telomerase recruitment. However, it remained unclear how telomere maintenance is dynamically regulated during the cell cycle. Thus, we investigated how loss of Poz1, Rap1 and Taz1 affects cell cycle regulation of Ccq1 Thr93 phosphorylation and telomere association of telomerase (Trt1TERT), DNA polymerases, Replication Protein A (RPA) complex, Rad3ATR-Rad26ATRIP checkpoint kinase complex, Tel1ATM kinase, shelterin subunits (Tpz1, Ccq1 and Poz1) and Stn1. We further investigated how telomere shortening, caused by trt1Δ or catalytically dead Trt1-D743A, affects cell cycle-regulated telomere association of telomerase and DNA polymerases. These analyses established that fission yeast shelterin maintains telomere length homeostasis by coordinating the differential arrival of leading (Polε) and lagging (Polα) strand DNA polymerases at telomeres to modulate Rad3ATR association, Ccq1 Thr93 phosphorylation and telomerase recruitment. Stable maintenance of telomeres is critical to maintain a stable genome and to prevent accumulation of undesired mutations that may lead to formation of tumors. Telomere dysfunction can also lead to premature aging due to depletion of the stem cell population, highlighting the importance of understanding the regulatory mechanisms that ensure stable telomere maintenance. Based on careful analysis of cell cycle-regulated changes in telomere association of telomerase, DNA polymerases, Replication Protein A, checkpoint kinases, telomere protection complex shelterin, and Stn1-Ten1 complex, we will provide here a new and dynamic model of telomere length regulation in fission yeast, which suggests that shelterin-dependent regulation of differential arrival of leading and lagging strand DNA polymerase at telomeres is responsible for modulating Rad3ATR checkpoint kinase accumulation and Rad3ATR-dependent phosphorylation of shelterin subunit Ccq1 to control telomerase recruitment to telomeres.
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Affiliation(s)
- Ya-Ting Chang
- Department of Biochemistry and Molecular Genetics, College of Medicine, University of Illinois at Chicago, Chicago, Illinois, United States of America
| | - Bettina A. Moser
- Department of Biochemistry and Molecular Genetics, College of Medicine, University of Illinois at Chicago, Chicago, Illinois, United States of America
| | - Toru M. Nakamura
- Department of Biochemistry and Molecular Genetics, College of Medicine, University of Illinois at Chicago, Chicago, Illinois, United States of America
- * E-mail:
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Teresa Avelar A, Perfeito L, Gordo I, Godinho Ferreira M. Genome architecture is a selectable trait that can be maintained by antagonistic pleiotropy. Nat Commun 2013; 4:2235. [DOI: 10.1038/ncomms3235] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2012] [Accepted: 07/03/2013] [Indexed: 12/29/2022] Open
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Webb CJ, Wu Y, Zakian VA. DNA repair at telomeres: keeping the ends intact. Cold Spring Harb Perspect Biol 2013; 5:5/6/a012666. [PMID: 23732473 DOI: 10.1101/cshperspect.a012666] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The molecular era of telomere biology began with the discovery that telomeres usually consist of G-rich simple repeats and end with 3' single-stranded tails. Enormous progress has been made in identifying the mechanisms that maintain and replenish telomeric DNA and the proteins that protect them from degradation, fusions, and checkpoint activation. Although telomeres in different organisms (or even in the same organism under different conditions) are maintained by different mechanisms, the disparate processes have the common goals of repairing defects caused by semiconservative replication through G-rich DNA, countering the shortening caused by incomplete replication, and postreplication regeneration of G tails. In addition, standard DNA repair mechanisms must be suppressed or modified at telomeres to prevent their being recognized and processed as DNA double-strand breaks. Here, we discuss the players and processes that maintain and regenerate telomere structure.
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Affiliation(s)
- Christopher J Webb
- Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544, USA
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31
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Almeida H, Godinho Ferreira M. Spontaneous telomere to telomere fusions occur in unperturbed fission yeast cells. Nucleic Acids Res 2013; 41:3056-67. [PMID: 23335786 PMCID: PMC3597658 DOI: 10.1093/nar/gks1459] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Telomeres protect eukaryotic chromosomes from illegitimate end-to-end fusions. When this function fails, dicentric chromosomes are formed, triggering breakage-fusion-bridge cycles and genome instability. How efficient is this protection mechanism in normal cells is not fully understood. We created a positive selection assay aimed at capturing chromosome-end fusions in Schizosaccharomyces pombe. We placed telomere sequences with a head to head arrangement in an intron of a selectable marker contained on a plasmid. By linearizing the plasmid between the telomere sequences, we generated a stable mini-chromosome that fails to express the reporter gene. Whenever the ends of the mini-chromosome join, the marker gene is reconstituted and fusions are captured by direct selection. Using telomerase mutants, we recovered several fusion events that lacked telomere sequences. The end-joining reaction involved specific homologous subtelomeric sequences capable of forming hairpins, suggestive of ssDNA stabilization prior to fusing. These events occurred via microhomology-mediated end-joining (MMEJ)/single-strand annealing (SSA) repair and also required MRN/Ctp1. Strikingly, we were able to capture spontaneous telomere-to-telomere fusions in unperturbed cells. Similar to disruption of the telomere regulator Taz1/TRF2, end-joining reactions occurred via non-homologous end-joining (NHEJ) repair. Thus, telomeres undergo fusions prior to becoming critically short, possibly through transient deprotection. These dysfunction events induce chromosome instability and may underlie early tumourigenesis.
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Affiliation(s)
- Hugo Almeida
- Instituto Gulbenkian de Ciência, Rua da Quinta Grande 6, 2780-156 Oeiras, Portugal
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32
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A single internal telomere tract ensures meiotic spindle formation. EMBO Rep 2013; 14:252-60. [PMID: 23295325 DOI: 10.1038/embor.2012.218] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2012] [Revised: 12/03/2012] [Accepted: 12/04/2012] [Indexed: 11/09/2022] Open
Abstract
Contact between telomeres and the fission yeast spindle pole body during meiotic prophase is crucial for subsequent spindle assembly, but the feature of telomeres that confers their ability to promote spindle formation remains mysterious. Here we show that while strains harbouring circular chromosomes devoid of telomere repeat tracts undergo aberrant meiosis with defective spindles, the insertion of a single internal telomere repeat stretch rescues the spindle defects. Moreover, the telomeric overhang-binding protein Pot1 is dispensable for rescue of spindle formation. Hence, an inherent feature of the double-strand telomeric region endows telomeres with the capacity to promote spindle formation.
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33
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Abstract
Telomeres protect the natural ends of chromosomes from being repaired as deleterious DNA breaks. In fission yeast, absence of Taz1 (homologue of human TRF1 and TRF2) renders telomeres vulnerable to DNA repair. During the G1 phase, when non-homologous end joining (NHEJ) is upregulated, taz1Δ cells undergo telomere fusions with consequent loss of viability. Here, we show that disruption of the fission yeast MRN (Rad23(MRE11)-Rad50-Nbs1) complex prevents NHEJ at telomeres and, as a result, rescues taz1Δ lethality in G1. Neither Tel1(ATM) activation nor 5'-end resection was required for telomere fusion. Nuclease activity of Rad32(MRE11) was also dispensable for NHEJ. Mutants unable to coordinate metal ions required for nuclease activity were proficient in NHEJ repair. In contrast, Rad32(MRE11) mutations that affect binding and/or positioning of DNA ends leaving the nuclease function largely unaffected also impaired NHEJ at telomeres and restored the viability of taz1Δ in G1. Consistently, MRN structural integrity but not nuclease function is also required for NHEJ of independent DNA ends in a novel split-molecule plasmid assay. Thus, MRN acts to tether unlinked DNA ends, allowing for efficient NHEJ.
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Fujita I, Tanaka M, Kanoh J. Identification of the functional domains of the telomere protein Rap1 in Schizosaccharomyces pombe. PLoS One 2012; 7:e49151. [PMID: 23133674 PMCID: PMC3487762 DOI: 10.1371/journal.pone.0049151] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2012] [Accepted: 10/04/2012] [Indexed: 01/10/2023] Open
Abstract
The telomere at the end of a linear chromosome plays crucial roles in genome stability. In the fission yeast Schizosaccharomyces pombe, the Rap1 protein, one of the central players at the telomeres, associates with multiple proteins to regulate various telomere functions, such as the maintenance of telomere DNA length, telomere end protection, maintenance of telomere heterochromatin, and telomere clustering in meiosis. The molecular bases of the interactions between Rap1 and its partners, however, remain largely unknown. Here, we describe the identification of the interaction domains of Rap1 with its partners. The Bqt1/Bqt2 complex, which is required for normal meiotic progression, Poz1, which is required for telomere length control, and Taz1, which is required for the recruitment of Rap1 to telomeres, bind to distinct domains in the C-terminal half of Rap1. Intriguingly, analyses of a series of deletion mutants for rap1+ have revealed that the long N-terminal region (1–456 a.a. [amino acids]) of Rap1 (full length: 693 a.a.) is not required for telomere DNA length control, telomere end protection, and telomere gene silencing, whereas the C-terminal region (457–693 a.a.) containing Poz1- and Taz1-binding domains plays important roles in those functions. Furthermore, the Bqt1/Bqt2- and Taz1-binding domains are essential for normal spore formation after meiosis. Our results suggest that the C-terminal half of Rap1 is critical for the primary telomere functions, whereas the N-terminal region containing the BRCT (BRCA1 C-terminus) and Myb domains, which are evolutionally conserved among the Rap1 family proteins, does not play a major role at the telomeres.
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Affiliation(s)
- Ikumi Fujita
- Institute for Protein Research, Osaka University, Suita, Osaka, Japan
| | - Makiko Tanaka
- Institute for Protein Research, Osaka University, Suita, Osaka, Japan
| | - Junko Kanoh
- Institute for Protein Research, Osaka University, Suita, Osaka, Japan
- * E-mail:
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Dehé PM, Rog O, Ferreira M, Greenwood J, Cooper J. Taz1 Enforces Cell-Cycle Regulation of Telomere Synthesis. Mol Cell 2012; 46:797-808. [DOI: 10.1016/j.molcel.2012.04.022] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2011] [Revised: 02/21/2012] [Accepted: 04/13/2012] [Indexed: 01/14/2023]
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Vannier JB, Pavicic-Kaltenbrunner V, Petalcorin MIR, Ding H, Boulton SJ. RTEL1 dismantles T loops and counteracts telomeric G4-DNA to maintain telomere integrity. Cell 2012; 149:795-806. [PMID: 22579284 DOI: 10.1016/j.cell.2012.03.030] [Citation(s) in RCA: 343] [Impact Index Per Article: 28.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2011] [Revised: 01/11/2012] [Accepted: 03/02/2012] [Indexed: 11/19/2022]
Abstract
T loops and telomeric G-quadruplex (G4) DNA structures pose a potential threat to genome stability and must be dismantled to permit efficient telomere replication. Here we implicate the helicase RTEL1 in the removal of telomeric DNA secondary structures, which is essential for preventing telomere fragility and loss. In the absence of RTEL1, T loops are inappropriately resolved by the SLX4 nuclease complex, resulting in loss of the telomere as a circle. Depleting SLX4 or blocking DNA replication abolished telomere circles (TCs) and rescued telomere loss in RTEL1(-/-) cells but failed to suppress telomere fragility. Conversely, stabilization of telomeric G4-DNA or loss of BLM dramatically enhanced telomere fragility in RTEL1-deficient cells but had no impact on TC formation or telomere loss. We propose that RTEL1 performs two distinct functions at telomeres: it disassembles T loops and also counteracts telomeric G4-DNA structures, which together ensure the dynamics and stability of the telomere.
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Affiliation(s)
- Jean-Baptiste Vannier
- DNA Damage Response laboratory, London Research Institute, Cancer Research UK, Clare Hall, South Mimms, UK
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37
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Arora R, Brun CMC, Azzalin CM. TERRA: Long Noncoding RNA at Eukaryotic Telomeres. PROGRESS IN MOLECULAR AND SUBCELLULAR BIOLOGY 2011; 51:65-94. [PMID: 21287134 DOI: 10.1007/978-3-642-16502-3_4] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Telomeres protect the ends of linear eukaryotic chromosomes from being recognized as DNA double-stranded breaks, thereby maintaining the stability of our genome. The highly heterochromatic nature of telomeres had, for a long time, reinforced the idea that telomeres were transcriptionally silent. Since a few years, however, we know that DNA-dependent RNA polymerase II transcribes telomeric DNA into TElomeric Repeat-containing RNA (TERRA) molecules in a large variety of eukaryotes. In this chapter, we summarize the current knowledge of telomere structure and function and extensively review data accumulated on TERRA biogenesis and regulation. We also discuss putative functions of TERRA in preserving telomere stability and propose future directions for research encompassing this novel and exciting aspect of telomere biology.
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Affiliation(s)
- Rajika Arora
- Institute of Biochemistry, ETHZ-Eidgenössische Technische Hochschule Zürich, CH-8093, Zürich, Switzerland
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38
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Affiliation(s)
- Devanshi Jain
- Telomere Biology Laboratory, Cancer Research UK, London Research Institute, London WC2A 3PX, United Kingdom;
| | - Julia Promisel Cooper
- Telomere Biology Laboratory, Cancer Research UK, London Research Institute, London WC2A 3PX, United Kingdom;
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39
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Carneiro T, Khair L, Reis CC, Borges V, Moser BA, Nakamura TM, Ferreira MG. Telomeres avoid end detection by severing the checkpoint signal transduction pathway. Nature 2010; 467:228-32. [PMID: 20829797 DOI: 10.1038/nature09353] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2009] [Accepted: 07/14/2010] [Indexed: 01/30/2023]
Abstract
Telomeres protect the normal ends of chromosomes from being recognized as deleterious DNA double-strand breaks. Recent studies have uncovered an apparent paradox: although DNA repair is prevented, several proteins involved in DNA damage processing and checkpoint responses are recruited to telomeres in every cell cycle and are required for end protection. It is currently not understood how telomeres prevent DNA damage responses from causing permanent cell cycle arrest. Here we show that fission yeast (Schizosaccharomyces pombe) cells lacking Taz1, an orthologue of human TRF1 and TRF2 (ref. 2), recruit DNA repair proteins (Rad22(RAD52) and Rhp51(RAD51), where the superscript indicates the human orthologue) and checkpoint sensors (RPA, Rad9, Rad26(ATRIP) and Cut5/Rad4(TOPBP1)) to telomeres. Despite this, telomeres fail to accumulate the checkpoint mediator Crb2(53BP1) and, consequently, do not activate Chk1-dependent cell cycle arrest. Artificially recruiting Crb2(53BP1) to taz1Δ telomeres results in a full checkpoint response and cell cycle arrest. Stable association of Crb2(53BP1) to DNA double-strand breaks requires two independent histone modifications: H4 dimethylation at lysine 20 (H4K20me2) and H2A carboxy-terminal phosphorylation (γH2A). Whereas γH2A can be readily detected, telomeres lack H4K20me2, in contrast to internal chromosome locations. Blocking checkpoint signal transduction at telomeres requires Pot1 and Ccq1, and loss of either Pot1 or Ccq1 from telomeres leads to Crb2(53BP1) foci formation, Chk1 activation and cell cycle arrest. Thus, telomeres constitute a chromatin-privileged region of the chromosomes that lack essential epigenetic markers for DNA damage response amplification and cell cycle arrest. Because the protein kinases ATM and ATR must associate with telomeres in each S phase to recruit telomerase, exclusion of Crb2(53BP1) has a critical role in preventing telomeres from triggering cell cycle arrest.
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Affiliation(s)
- Tiago Carneiro
- Instituto Gulbenkian de Ciência, Oeiras 2781-901, Portugal
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40
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HAATI survivors replace canonical telomeres with blocks of generic heterochromatin. Nature 2010; 467:223-7. [DOI: 10.1038/nature09374] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2009] [Accepted: 07/21/2010] [Indexed: 01/25/2023]
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41
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Giraud-Panis MJ, Pisano S, Poulet A, Le Du MH, Gilson E. Structural identity of telomeric complexes. FEBS Lett 2010; 584:3785-99. [PMID: 20696167 DOI: 10.1016/j.febslet.2010.08.004] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2010] [Revised: 08/02/2010] [Accepted: 08/02/2010] [Indexed: 02/01/2023]
Abstract
A major issue in telomere research is to understand how the integrity of chromosome ends is controlled. Although several nucleoprotein complexes have been described at the telomeres of different organisms, it is still unclear how they confer a structural identity to chromosome ends in order to mask them from DNA repair and to ensure their proper replication. In this review, we describe how telomeric nucleoprotein complexes are structured, comparing different organisms and trying to link these structures to telomere biology. It emerges that telomeres are formed by a complex and specific network of interactions between DNA, RNA and proteins. The fact that these interactions and associated activities are reinforcing each other might help to guaranty the robustness of telomeric functions across the cell cycle and in the event of cellular perturbations. We propose that telomeric nucleoprotein complexes orient cell fate through dynamic transitions in their structures and their organization.
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Affiliation(s)
- Marie-Josèphe Giraud-Panis
- University de Nice, Laboratory of Biology and Pathology of Genomes, UMR 6267 CNRS U998 INSERM, Faculté de Médecine, Nice, France
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42
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Dehé PM, Cooper JP. Fission yeast telomeres forecast the end of the crisis. FEBS Lett 2010; 584:3725-33. [PMID: 20682311 DOI: 10.1016/j.febslet.2010.07.045] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2010] [Revised: 07/27/2010] [Accepted: 07/27/2010] [Indexed: 10/19/2022]
Abstract
Recent years have placed fission yeast at the forefront of telomere research, as this organism combines a high level of conservation with human telomeres and precise genetic manipulability. Here we highlight some of the latest knowledge of fission yeast telomere maintenance and dysfunction, and illustrate how principles arising from fission yeast research are raising novel questions about telomere plasticity and function in all eukaryotes.
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Affiliation(s)
- Pierre-Marie Dehé
- Telomere Biology Laboratory, Cancer Research UK, London, United Kingdom
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43
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Telomere capping in non-dividing yeast cells requires Yku and Rap1. EMBO J 2010; 29:3007-19. [PMID: 20628356 DOI: 10.1038/emboj.2010.155] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2009] [Accepted: 06/18/2010] [Indexed: 01/13/2023] Open
Abstract
The assembly of a protective cap onto the telomeres of eukaryotic chromosomes suppresses genomic instability through inhibition of DNA repair activities that normally process accidental DNA breaks. We show here that the essential Cdc13-Stn1-Ten1 complex is entirely dispensable for telomere protection in non-dividing cells. However, Yku and Rap1 become crucially important for this function in these cells. After inactivation of Yku70 in G1-arrested cells, moderate but significant telomere degradation occurs. As the activity of cyclin-dependent kinases (CDK) promotes degradation, these results suggest that Yku stabilizes G1 telomeres by blocking the access of CDK1-independent nucleases to telomeres. The results indeed show that both Exo1 and the Mre11/Rad50/Xrs2 complex are required for telomeric resection after Yku loss in non-dividing cells. Unexpectedly, both asynchronously growing and quiescent G0 cells lacking Rap1 display readily detectable telomere degradation, suggesting an earlier unanticipated function for this protein in suppression of nuclease activities at telomeres. Together, our results show a high flexibility of the telomeric cap and suggest that distinct configurations may provide for efficient capping in dividing versus non-dividing cells.
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44
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Pitt CW, Cooper JP. Pot1 inactivation leads to rampant telomere resection and loss in one cell cycle. Nucleic Acids Res 2010; 38:6968-75. [PMID: 20601686 PMCID: PMC2978358 DOI: 10.1093/nar/gkq580] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Removal of the conserved telomere protein, Pot1, confers the immediate loss of fission yeast telomeres. This drastic phenotype has established the centrality of Pot1 for telomere maintenance but prohibited elucidation of the intermediate steps leading to telomere loss. To circumvent this problem, we have generated a conditional allele, pot1–1. We show that loss of Pot1 function during G1 leads to rapid telomere erosion during the ensuing S/G2 period. Precipitous telomere loss depends upon S-phase progression and is preceded by 5′ telomeric resection. Telomere loss is accompanied by ATR- and Chk1-mediated checkpoint activation, but is not caused by checkpoint arrest.
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45
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SNMIB/Apollo protects leading-strand telomeres against NHEJ-mediated repair. EMBO J 2010; 29:2230-41. [PMID: 20551906 DOI: 10.1038/emboj.2010.58] [Citation(s) in RCA: 90] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2010] [Accepted: 05/19/2010] [Indexed: 11/08/2022] Open
Abstract
Progressive telomere attrition or deficiency of the protective shelterin complex elicits a DNA damage response as a result of a cell's inability to distinguish dysfunctional telomeric ends from DNA double-strand breaks. SNMIB/Apollo is a shelterin-associated protein and a member of the SMN1/PSO2 nuclease family that localizes to telomeres through its interaction with TRF2. Here, we generated SNMIB/Apollo knockout mouse embryo fibroblasts (MEFs) to probe the function of SNMIB/Apollo at mammalian telomeres. SNMIB/Apollo null MEFs exhibit an increased incidence of G2 chromatid-type fusions involving telomeres created by leading-strand DNA synthesis, reflective of a failure to protect these telomeres after DNA replication. Mutations within SNMIB/Apollo's conserved nuclease domain failed to suppress this phenotype, suggesting that its nuclease activity is required to protect leading-strand telomeres. SNMIB/Apollo(-/-)ATM(-/-) MEFs display robust telomere fusions when Trf2 is depleted, indicating that ATM is dispensable for repair of uncapped telomeres in this setting. Our data implicate the 5'-3' exonuclease function of SNM1B/Apollo in the generation of 3' single-stranded overhangs at newly replicated leading-strand telomeres to protect them from engaging the non-homologous end-joining pathway.
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46
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Kinsky S, Mihalikova A, Kramara J, Nosek J, Tomaska L. Lack of the catalytic subunit of telomerase leads to growth defects accompanied by structural changes at the chromosomal ends in Yarrowia lipolytica. Curr Genet 2010; 56:413-25. [PMID: 20549213 DOI: 10.1007/s00294-010-0310-6] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2010] [Revised: 05/26/2010] [Accepted: 05/28/2010] [Indexed: 12/01/2022]
Abstract
Comparative analysis of the telomeres of distantly related species has proven to be helpful for identifying novel components involved in telomere maintenance. We therefore initiated such a study in the nonconventional yeast Yarrowia lipolytica. Its genome encodes only a small fraction of the proteins that are typically associated with telomeres in other yeast models, indicating that its telomeres may employ noncanonical means for their stabilization and maintenance. In this report, we have measured the size of the telomeric fragments in wild-type strains, and characterized the catalytic subunit of telomerase (YlEst2p). In silico analysis of the YlEst2 amino acid sequence revealed the presence of domains typical for telomerase reverse transcriptases. Disruption of YlEST2 is not lethal, but results in retarded growth accompanied by a rapid loss of the telomeric sequences. This phenotype is associated with structural changes at the chromosomal ends in the ΔYlest2 mutants, likely the circularization of all six chromosomes. An apparent absence of several typical telomere-associated factors, as well as the presence of an efficient means of telomerase-independent telomere maintenance, qualify Y. lipolytica as an attractive model for the study of telomere maintenance mechanisms and a promising source of novel players in telomere dynamics.
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Affiliation(s)
- Slavomir Kinsky
- Department of Genetics, Comenius University, Bratislava, Slovakia
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47
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Subramanian L, Nakamura TM. To fuse or not to fuse: how do checkpoint and DNA repair proteins maintain telomeres? FRONT BIOSCI-LANDMRK 2010; 15:1105-18. [PMID: 20515744 PMCID: PMC2880829 DOI: 10.2741/3664] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
DNA damage checkpoint and DNA repair mechanisms play critical roles in the stable maintenance of genetic information. Various forms of DNA damage that arise inside cells due to common errors in normal cellular processes, such as DNA replication, or due to exposure to various DNA damaging agents, must be quickly detected and repaired by checkpoint signaling and repair factors. Telomeres, the natural ends of linear chromosomes, share many features with undesired "broken" DNA, and are recognized and processed by various DNA damage checkpoint and DNA repair proteins. However, their modes of action at telomeres must be altered from their actions at other DNA damage sites to avoid telomere fusions and permanent cell cycle arrest. Interestingly, accumulating evidence indicates that DNA damage checkpoint and DNA repair proteins are essential for telomere maintenance. In this article, we review our current knowledge on various mechanisms by which DNA damage checkpoint and DNA repair proteins are modulated at telomeres and how they might contribute to telomere maintenance in eukaryotes.
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Affiliation(s)
- Lakxmi Subramanian
- Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago, Chicago, IL 60607, USA
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48
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Abstract
Nonhomologous end-joining (NHEJ) inhibition at telomeres ensures that native chromosome ends do not fuse together. But the occurrence and consequences of rare telomere fusions are not well understood. It is notably unclear whether a telomere fusion could be processed to restore telomere ends. Here we address the behavior of individual dicentrics formed by telomere fusion in the yeast Saccharomyces cerevisiae. Our approach was to first stabilize and amplify fusions between two chromosomes by temporarily inactivating one centromere. Next we analyzed dicentric breakage following centromere reactivation. Unexpectedly, dicentrics often break at the telomere fusions during progression through mitosis, a process that restores the parental chromosomes. This unforeseen result suggests a rescue pathway able to process telomere fusions and to back up NHEJ inhibition at telomeres.
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Affiliation(s)
- Sabrina Pobiega
- Commissariat à l'Energie Atomique, Direction des Sciences du Vivant, Institut de Radiobiologie Cellulaire et Moléculaire, Service Instabilité Génétique Réparation et Recombinaison, Laboratoire Télmère et Réparation du Chromosome, Fontenay-aux-roses 92260, France
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Gunisova S, Bartosova Z, Kramara J, Nosek J, Tomaska L. Formation of C-terminally truncated version of the Taz1 protein employs cleavage-box structure in mRNA. Biochem Biophys Res Commun 2010; 392:391-6. [PMID: 20074552 DOI: 10.1016/j.bbrc.2010.01.033] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2010] [Accepted: 01/08/2010] [Indexed: 10/20/2022]
Abstract
When expressed in various hosts the taz1(+) gene encoding the fission yeast telomere-binding protein produces two forms of polypeptides: full-length (Taz1p) and truncated (Taz1pDeltaC) version lacking almost entire Myb-domain. Whereas Taz1p binds telomeric DNA in vitro, Taz1pDeltaC forms long filaments unable of DNA binding. The formation of Taz1pDeltaC is a result of neither site-specific proteolysis, nor premature termination of transcription. In silico analysis of the taz1(+) RNA transcript revealed a stem-loop structure at the site of cleavage (cleavage box; CB). In order to explore whether it possesses inherent destabilizing effects, we cloned CB sequence into the open reading frame (ORF) of glutathione-S-transferase (GST) and observed that when expressed in Escherichia coli the engineered gene produced two forms of the reporter protein. The formation of the truncated version of GST was abolished, when CB was replaced with recoded sequence containing synonymous codons thus indicating that the truncation is based on structural properties of taz1(+) mRNA.
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HipHop interacts with HOAP and HP1 to protect Drosophila telomeres in a sequence-independent manner. EMBO J 2010; 29:819-29. [PMID: 20057353 DOI: 10.1038/emboj.2009.394] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2009] [Accepted: 12/08/2009] [Indexed: 12/30/2022] Open
Abstract
Telomeres prevent chromosome ends from being repaired as double-strand breaks (DSBs). Telomere identity in Drosophila is determined epigenetically with no sequence either necessary or sufficient. To better understand this sequence-independent capping mechanism, we isolated proteins that interact with the HP1/ORC-associated protein (HOAP) capping protein, and identified HipHop as a subunit of the complex. Loss of one protein destabilizes the other and renders telomeres susceptible to fusion. Both HipHop and HOAP are enriched at telomeres, where they also interact with the conserved HP1 protein. We developed a model telomere lacking repetitive sequences to study the distribution of HipHop, HOAP and HP1 using chromatin immunoprecipitation (ChIP). We discovered that they occupy a broad region >10 kb from the chromosome end and their binding is independent of the underlying DNA sequence. HipHop and HOAP are both rapidly evolving proteins yet their telomeric deposition is under the control of the conserved ATM and Mre11-Rad50-Nbs (MRN) proteins that modulate DNA structures at telomeres and at DSBs. Our characterization of HipHop and HOAP reveals functional analogies between the Drosophila proteins and subunits of the yeast and mammalian capping complexes, implicating conservation in epigenetic capping mechanisms.
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