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Hao H, Ren C, Lian Y, Zhao M, Bo T, Xu J, Wang W. Independent and Complementary Functions of Caf1b and Hir1 for Chromatin Assembly in Tetrahymena thermophila. Cells 2023; 12:2828. [PMID: 38132148 PMCID: PMC10741905 DOI: 10.3390/cells12242828] [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: 11/17/2023] [Revised: 12/09/2023] [Accepted: 12/11/2023] [Indexed: 12/23/2023] Open
Abstract
Histones and DNA associate to form the nucleosomes of eukaryotic chromatin. Chromatin assembly factor 1 (CAF-1) complex and histone regulatory protein A (HIRA) complex mediate replication-couple (RC) and replication-independent (RI) nucleosome assembly, respectively. CHAF1B and HIRA share a similar domain but play different roles in nucleosome assembly by binding to the different interactors. At present, there is limited understanding for the similarities and differences in their respective functions. Tetrahymena thermophila contains transcriptionally active polyploid macronuclei (MAC) and transcriptionally silent diploid micronuclei (MIC). Here, the distribution patterns of Caf1b and Hir1 exhibited both similarities and distinctions. Both proteins localized to the MAC and MIC during growth, and to the MIC during conjugation. However, Hir1 exhibited additional signaling on parental MAC and new MAC during sexual reproduction and displayed a punctate signal on developing anlagen. Caf1b and Hir1 only co-localized in the MIC with Pcna1 during conjugation. Knockdown of CAF1B impeded cellular growth and arrested sexual reproductive development. Loss of HIR1 led to MIC chromosome defects and aborted sexual development. Co-interference of CAF1B and HIR1 led to a more severe phenotype. Moreover, CAF1B knockdown led to the up-regulation of HIR1 expression, while knockdown of HIR1 also led to an increase in CAF1B expression. Furthermore, Caf1b and Hir1 interacted with different interactors. These results showed that CAF-1 and Hir1 have independent and complementary functions for chromatin assembly in T. thermophila.
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Affiliation(s)
- Huijuan Hao
- Key Laboratory of Chemical Biology and Molecular Engineering of Ministry of Education, Institute of Biotechnology, Shanxi University, Taiyuan 030006, China; (H.H.); (C.R.); (Y.L.); (M.Z.); (T.B.)
| | - Chenhui Ren
- Key Laboratory of Chemical Biology and Molecular Engineering of Ministry of Education, Institute of Biotechnology, Shanxi University, Taiyuan 030006, China; (H.H.); (C.R.); (Y.L.); (M.Z.); (T.B.)
| | - Yinjie Lian
- Key Laboratory of Chemical Biology and Molecular Engineering of Ministry of Education, Institute of Biotechnology, Shanxi University, Taiyuan 030006, China; (H.H.); (C.R.); (Y.L.); (M.Z.); (T.B.)
| | - Min Zhao
- Key Laboratory of Chemical Biology and Molecular Engineering of Ministry of Education, Institute of Biotechnology, Shanxi University, Taiyuan 030006, China; (H.H.); (C.R.); (Y.L.); (M.Z.); (T.B.)
| | - Tao Bo
- Key Laboratory of Chemical Biology and Molecular Engineering of Ministry of Education, Institute of Biotechnology, Shanxi University, Taiyuan 030006, China; (H.H.); (C.R.); (Y.L.); (M.Z.); (T.B.)
| | - Jing Xu
- Key Laboratory of Chemical Biology and Molecular Engineering of Ministry of Education, Institute of Biotechnology, Shanxi University, Taiyuan 030006, China; (H.H.); (C.R.); (Y.L.); (M.Z.); (T.B.)
- School of Life Science, Shanxi University, Taiyuan 030006, China
| | - Wei Wang
- Key Laboratory of Chemical Biology and Molecular Engineering of Ministry of Education, Institute of Biotechnology, Shanxi University, Taiyuan 030006, China; (H.H.); (C.R.); (Y.L.); (M.Z.); (T.B.)
- Shanxi Key Laboratory of Biotechnology, Taiyuan 030006, China
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Lu MW, Beh LY, Yerlici VT, Fang W, Kulej K, Garcia BA, Landweber LF. Exploration of the Nuclear Proteomes in the Ciliate Oxytricha trifallax. Microorganisms 2023; 11:microorganisms11020343. [PMID: 36838311 PMCID: PMC9958989 DOI: 10.3390/microorganisms11020343] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2022] [Revised: 01/17/2023] [Accepted: 01/21/2023] [Indexed: 01/31/2023] Open
Abstract
Nuclear dimorphism is a fundamental feature of ciliated protozoa, which have separate somatic and germline genomes in two distinct organelles within a single cell. The transcriptionally active somatic genome, contained within the physically larger macronucleus, is both structurally and functionally different from the silent germline genome housed in the smaller micronucleus. This difference in genome architecture is particularly exaggerated in Oxytricha trifallax, in which the somatic genome comprises tens of thousands of gene-sized nanochromosomes maintained at a high and variable ploidy, while the germline has a diploid set of megabase-scale chromosomes. To examine the compositional differences between the nuclear structures housing the genomes, we performed a proteomic survey of both types of nuclei and of macronuclear histones using quantitative mass spectrometry. We note distinct differences between the somatic and germline nuclei, with many functional proteins being highly enriched in one of the two nuclei. To validate our conclusions and the efficacy of nuclear separation, we used protein localization through a combination of transformations and immunofluorescence. We also note that the macronuclear histones strikingly display only activating marks, consistent with the conclusion that the macronucleus is the hub of transcription. These observations suggest that the compartmentalization of different genome features into separate structures has been accompanied by a similar specialization of nuclear components that maintain and facilitate the functions of the genomes specific to each nucleus.
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Affiliation(s)
- Michael W. Lu
- Department of Biological Sciences, Columbia University, New York, NY 10025, USA
| | - Leslie Y. Beh
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - V. Talya Yerlici
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Wenwen Fang
- RNA Therapeutics Institute, UMass Chan Medical School, Worcester, MA 01655, USA
| | - Katarzyna Kulej
- Division of Protective Immunity and Division of Cancer Pathobiology, The Children’s Hospital of Philadelphia, Philadelphia, PA 19104, USA
| | - Benjamin A. Garcia
- Department of Biochemistry and Molecular Biophysics, Washington University in St. Louis, St. Louis, MO 63130, USA
| | - Laura F. Landweber
- Department of Biological Sciences, Columbia University, New York, NY 10025, USA
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
- Correspondence:
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Zhang L, Cervantes MD, Pan S, Lindsley J, Dabney A, Kapler GM. Transcriptome analysis of the binucleate ciliate Tetrahymena thermophila with asynchronous nuclear cell cycles. Mol Biol Cell 2023; 34:rs1. [PMID: 36475712 PMCID: PMC9930529 DOI: 10.1091/mbc.e22-08-0326] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Tetrahymena thermophila harbors two functionally and physically distinct nuclei within a shared cytoplasm. During vegetative growth, the "cell cycles" of the diploid micronucleus and polyploid macronucleus are offset. Micronuclear S phase initiates just before cytokinesis and is completed in daughter cells before onset of macronuclear DNA replication. Mitotic micronuclear division occurs mid-cell cycle, while macronuclear amitosis is coupled to cell division. Here we report the first RNA-seq cell cycle analysis of a binucleated ciliated protozoan. RNA was isolated across 1.5 vegetative cell cycles, starting with a macronuclear G1 population synchronized by centrifugal elutriation. Using MetaCycle, 3244 of the 26,000+ predicted genes were shown to be cell cycle regulated. Proteins present in both nuclei exhibit a single mRNA peak that always precedes their macronuclear function. Nucleus-limited genes, including nucleoporins and importins, are expressed before their respective nucleus-specific role. Cyclin D and A/B gene family members exhibit different expression patterns that suggest nucleus-restricted roles. Periodically expressed genes cluster into seven cyclic patterns. Four clusters have known PANTHER gene ontology terms associated with G1/S and G2/M phase. We propose that these clusters encode known and novel factors that coordinate micro- and macronuclear-specific events such as mitosis, amitosis, DNA replication, and cell division.
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Affiliation(s)
- L. Zhang
- Department of Cell Biology and Genetics, Texas A&M University Health Science Center, College Station, TX 77840,Department of Statistics, Texas A&M University, College Station, TX 77843
| | - M. D. Cervantes
- Department of Cell Biology and Genetics, Texas A&M University Health Science Center, College Station, TX 77840
| | - S. Pan
- Department of Cell Biology and Genetics, Texas A&M University Health Science Center, College Station, TX 77840,Department of Statistics, Texas A&M University, College Station, TX 77843
| | - J. Lindsley
- Department of Cell Biology and Genetics, Texas A&M University Health Science Center, College Station, TX 77840
| | - A. Dabney
- Department of Statistics, Texas A&M University, College Station, TX 77843,*Address correspondence to: Geoffrey Kapler (); A. Dabney ()
| | - G. M. Kapler
- Department of Cell Biology and Genetics, Texas A&M University Health Science Center, College Station, TX 77840,*Address correspondence to: Geoffrey Kapler (); A. Dabney ()
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Tian M, Cai X, Liu Y, Liucong M, Howard-Till R. A practical reference for studying meiosis in the model ciliate Tetrahymena thermophila. MARINE LIFE SCIENCE & TECHNOLOGY 2022; 4:595-608. [PMID: 37078080 PMCID: PMC10077211 DOI: 10.1007/s42995-022-00149-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/05/2022] [Accepted: 09/28/2022] [Indexed: 05/03/2023]
Abstract
Meiosis is a critical cell division program that produces haploid gametes for sexual reproduction. Abnormalities in meiosis are often causes of infertility and birth defects (e.g., Down syndrome). Most organisms use a highly specialized zipper-like protein complex, the synaptonemal complex (SC), to guide and stabilize pairing of homologous chromosomes in meiosis. Although the SC is critical for meiosis in many eukaryotes, there are organisms that perform meiosis without a functional SC. However, such SC-less meiosis is poorly characterized. To understand the features of SC-less meiosis and its adaptive significance, the ciliated protozoan Tetrahymena was selected as a model. Meiosis research in Tetrahymena has revealed intriguing aspects of the regulatory programs utilized in its SC-less meiosis, yet additional efforts are needed for obtaining an in-depth comprehension of mechanisms that are associated with the absence of SC. Here, aiming at promoting a wider application of Tetrahymena for meiosis research, we introduce basic concepts and core techniques for studying meiosis in Tetrahymena and then suggest future directions for expanding the current Tetrahymena meiosis research toolbox. These methodologies could be adopted for dissecting meiosis in poorly characterized ciliates that might reveal novel features. Such data will hopefully provide insights into the function of the SC and the evolution of meiosis from a unique perspective. Supplementary Information The online version contains supplementary material available at 10.1007/s42995-022-00149-8.
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Affiliation(s)
- Miao Tian
- Institute of Evolution & Marine Biodiversity, Ocean University of China, Qingdao, 266003 China
- Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao, 266237 China
- Institute of Human Genetics, CNRS, University of Montpellier, 34090 Montpellier, France
| | - Xia Cai
- Institute of Evolution & Marine Biodiversity, Ocean University of China, Qingdao, 266003 China
- Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao, 266237 China
| | - Yujie Liu
- Institute of Evolution & Marine Biodiversity, Ocean University of China, Qingdao, 266003 China
- Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao, 266237 China
| | - Mingmei Liucong
- Institute of Evolution & Marine Biodiversity, Ocean University of China, Qingdao, 266003 China
- Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao, 266237 China
| | - Rachel Howard-Till
- Department of Molecular and Cellular Biology, University of California Davis, Davis, CA USA
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5
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Sridhar S, Fukagawa T. Kinetochore Architecture Employs Diverse Linker Strategies Across Evolution. Front Cell Dev Biol 2022; 10:862637. [PMID: 35800888 PMCID: PMC9252888 DOI: 10.3389/fcell.2022.862637] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2022] [Accepted: 05/23/2022] [Indexed: 01/09/2023] Open
Abstract
The assembly of a functional kinetochore on centromeric chromatin is necessary to connect chromosomes to the mitotic spindle, ensuring accurate chromosome segregation. This connecting function of the kinetochore presents multiple internal and external structural challenges. A microtubule interacting outer kinetochore and centromeric chromatin interacting inner kinetochore effectively confront forces from the external spindle and centromere, respectively. While internally, special inner kinetochore proteins, defined as “linkers,” simultaneously interact with centromeric chromatin and the outer kinetochore to enable association with the mitotic spindle. With the ability to simultaneously interact with outer kinetochore components and centromeric chromatin, linker proteins such as centromere protein (CENP)-C or CENP-T in vertebrates and, additionally CENP-QOkp1-UAme1 in yeasts, also perform the function of force propagation within the kinetochore. Recent efforts have revealed an array of linker pathways strategies to effectively recruit the largely conserved outer kinetochore. In this review, we examine these linkages used to propagate force and recruit the outer kinetochore across evolution. Further, we look at their known regulatory pathways and implications on kinetochore structural diversity and plasticity.
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Lian Y, Hao H, Xu J, Bo T, Liang A, Wang W. The histone chaperone Nrp1 is required for chromatin stability and nuclear division in Tetrahymena thermophila. Epigenetics Chromatin 2021; 14:34. [PMID: 34301312 PMCID: PMC8299592 DOI: 10.1186/s13072-021-00409-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2021] [Accepted: 07/06/2021] [Indexed: 12/23/2022] Open
Abstract
Histone chaperones facilitate DNA replication and repair by promoting chromatin assembly, disassembly and histone exchange. Following histones synthesis and nucleosome assembly, the histones undergo posttranslational modification by different enzymes and are deposited onto chromatins by various histone chaperones. In Tetrahymena thermophila, histones from macronucleus (MAC) and micronucleus (MIC) have been comprehensively investigated, but the function of histone chaperones remains unclear. Histone chaperone Nrp1 in Tetrahymena contains four conserved tetratricopepeptide repeat (TPR) domains and one C-terminal nuclear localization signal. TPR2 is typically interrupted by a large acidic motif. Immunofluorescence staining showed that Nrp1 is located in the MAC and MICs, but disappeared in the apoptotic parental MAC and the degraded MICs during the conjugation stage. Nrp1 was also colocalized with α-tubulin around the spindle structure. NRP1 knockdown inhibited cellular proliferation and led to the loss of chromosome, abnormal macronuclear amitosis, and disorganized micronuclear mitosis during the vegetative growth stage. During sexual developmental stage, the gametic nuclei failed to be selected and abnormally degraded in NRP1 knockdown mutants. Affinity purification combined with mass spectrometry analysis indicated that Nrp1 is co-purified with core histones, heat shock proteins, histone chaperones, and DNA damage repair proteins. The physical direct interaction of Nrp1 and Asf1 was also confirmed by pull-down analysis in vitro. The results show that histone chaperone Nrp1 is involved in micronuclear mitosis and macronuclear amitosis in the vegetative growth stage and maintains gametic nuclei formation during the sexual developmental stage. Nrp1 is required for chromatin stability and nuclear division in Tetrahymena thermophila.
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Affiliation(s)
- Yinjie Lian
- Key Laboratory of Chemical Biology and Molecular Engineering of Ministry of Education, Institute of Biotechnology, Shanxi University, 92 Wucheng Rd., Taiyuan, 030006, China
| | - Huijuan Hao
- Key Laboratory of Chemical Biology and Molecular Engineering of Ministry of Education, Institute of Biotechnology, Shanxi University, 92 Wucheng Rd., Taiyuan, 030006, China
| | - Jing Xu
- Key Laboratory of Chemical Biology and Molecular Engineering of Ministry of Education, Institute of Biotechnology, Shanxi University, 92 Wucheng Rd., Taiyuan, 030006, China.,School of Life Science, Shanxi University, Taiyuan, 030006, China
| | - Tao Bo
- Key Laboratory of Chemical Biology and Molecular Engineering of Ministry of Education, Institute of Biotechnology, Shanxi University, 92 Wucheng Rd., Taiyuan, 030006, China
| | - Aihua Liang
- Key Laboratory of Chemical Biology and Molecular Engineering of Ministry of Education, Institute of Biotechnology, Shanxi University, 92 Wucheng Rd., Taiyuan, 030006, China
| | - Wei Wang
- Key Laboratory of Chemical Biology and Molecular Engineering of Ministry of Education, Institute of Biotechnology, Shanxi University, 92 Wucheng Rd., Taiyuan, 030006, China.
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7
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Lee SR, Pollard DA, Galati DF, Kelly ML, Miller B, Mong C, Morris MN, Roberts-Nygren K, Kapler GM, Zinkgraf M, Dang HQ, Branham E, Sasser J, Tessier E, Yoshiyama C, Matsumoto M, Turman G. Disruption of a ∼23-24 nucleotide small RNA pathway elevates DNA damage responses in Tetrahymena thermophila. Mol Biol Cell 2021; 32:1335-1346. [PMID: 34010017 PMCID: PMC8694037 DOI: 10.1091/mbc.e20-10-0631] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Endogenous RNA interference (RNAi) pathways regulate a wide range of cellular processes in diverse eukaryotes, yet in the ciliated eukaryote, Tetrahymena thermophila, the cellular purpose of RNAi pathways that generate ∼23–24 nucleotide (nt) small (s)RNAs has remained unknown. Here, we investigated the phenotypic and gene expression impacts on vegetatively growing cells when genes involved in ∼23–24 nt sRNA biogenesis are disrupted. We observed slower proliferation and increased expression of genes involved in DNA metabolism and chromosome organization and maintenance in sRNA biogenesis mutants RSP1Δ, RDN2Δ, and RDF2Δ. In addition, RSP1Δ and RDN2Δ cells frequently exhibited enlarged chromatin extrusion bodies, which are nonnuclear, DNA-containing structures that may be akin to mammalian micronuclei. Expression of homologous recombination factor Rad51 was specifically elevated in RSP1Δ and RDN2Δ strains, with Rad51 and double-stranded DNA break marker γ-H2A.X localized to discrete macronuclear foci. In addition, an increase in Rad51 and γ-H2A.X foci was also found in knockouts of TWI8, a macronucleus-localized PIWI protein. Together, our findings suggest that an evolutionarily conserved role for RNAi pathways in maintaining genome integrity may be extended even to the early branching eukaryotic lineage that gave rise to Tetrahymena thermophila.
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Affiliation(s)
- Suzanne R Lee
- Biology Department, Western Washington University, Bellingham, WA 98225
| | - Daniel A Pollard
- Biology Department, Western Washington University, Bellingham, WA 98225
| | - Domenico F Galati
- Biology Department, Western Washington University, Bellingham, WA 98225
| | - Megan L Kelly
- Biology Department, Western Washington University, Bellingham, WA 98225
| | - Brian Miller
- Biology Department, Western Washington University, Bellingham, WA 98225
| | - Christina Mong
- Biology Department, Western Washington University, Bellingham, WA 98225
| | - Megan N Morris
- Biology Department, Western Washington University, Bellingham, WA 98225
| | | | - Geoffrey M Kapler
- Molecular and Cellular Medicine, Texas A&M University, College Station, TX 77843
| | - Matthew Zinkgraf
- Biology Department, Western Washington University, Bellingham, WA 98225
| | - Hung Q Dang
- Molecular and Cellular Medicine, Texas A&M University, College Station, TX 77843
| | - Erica Branham
- Molecular and Cellular Medicine, Texas A&M University, College Station, TX 77843
| | - Jason Sasser
- Biology Department, Western Washington University, Bellingham, WA 98225
| | - Erin Tessier
- Biology Department, Western Washington University, Bellingham, WA 98225
| | | | - Maya Matsumoto
- Biology Department, Western Washington University, Bellingham, WA 98225
| | - Gaea Turman
- Biology Department, Western Washington University, Bellingham, WA 98225
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Tian M, Agreiter C, Loidl J. Spatial constraints on chromosomes are instrumental to meiotic pairing. J Cell Sci 2020; 133:jcs253724. [PMID: 33172984 PMCID: PMC7725606 DOI: 10.1242/jcs.253724] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2020] [Accepted: 10/29/2020] [Indexed: 01/10/2023] Open
Abstract
In most eukaryotes, the meiotic chromosomal bouquet (comprising clustered chromosome ends) provides an ordered chromosome arrangement that facilitates pairing and recombination between homologous chromosomes. In the protist Tetrahymena thermophila, the meiotic prophase nucleus stretches enormously, and chromosomes assume a bouquet-like arrangement in which telomeres and centromeres are attached to opposite poles of the nucleus. We have identified and characterized three meiosis-specific genes [meiotic nuclear elongation 1-3 (MELG1-3)] that control nuclear elongation, and centromere and telomere clustering. The Melg proteins interact with cytoskeletal and telomere-associated proteins, and probably repurpose them for reorganizing the meiotic prophase nucleus. A lack of sequence similarity between the Tetrahymena proteins responsible for telomere clustering and bouquet proteins of other organisms suggests that the Tetrahymena bouquet is analogous, rather than homologous, to the conserved eukaryotic bouquet. We also report that centromere clustering is more important than telomere clustering for homologous pairing. Therefore, we speculate that centromere clustering may have been the primordial mechanism for chromosome pairing in early eukaryotes.
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Affiliation(s)
- Miao Tian
- Department of Chromosome Biology, Max Perutz Laboratories, University of Vienna, A-1030 Vienna, Austria
| | - Christiane Agreiter
- Department of Chromosome Biology, Max Perutz Laboratories, University of Vienna, A-1030 Vienna, Austria
| | - Josef Loidl
- Department of Chromosome Biology, Max Perutz Laboratories, University of Vienna, A-1030 Vienna, Austria
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Wahab S, Saettone A, Nabeel-Shah S, Dannah N, Fillingham J. Exploring the Histone Acetylation Cycle in the Protozoan Model Tetrahymena thermophila. Front Cell Dev Biol 2020; 8:509. [PMID: 32695779 PMCID: PMC7339932 DOI: 10.3389/fcell.2020.00509] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2020] [Accepted: 05/28/2020] [Indexed: 12/22/2022] Open
Abstract
The eukaryotic histone acetylation cycle is composed of three classes of proteins, histone acetyltransferases (HATs) that add acetyl groups to lysine amino acids, bromodomain (BRD) containing proteins that are one of the most characterized of several protein domains that recognize acetyl-lysine (Kac) and effect downstream function, and histone deacetylases (HDACs) that catalyze the reverse reaction. Dysfunction of selected proteins of these three classes is associated with human disease such as cancer. Additionally, the HATs, BRDs, and HDACs of fungi and parasitic protozoa present potential drug targets. Despite their importance, the function and mechanisms of HATs, BRDs, and HDACs and how they relate to chromatin remodeling (CR) remain incompletely understood. Tetrahymena thermophila (Tt) provides a highly tractable single-celled free-living protozoan model for studying histone acetylation, featuring a massively acetylated somatic genome, a property that was exploited in the identification of the first nuclear/type A HAT Gcn5 in the 1990s. Since then, Tetrahymena remains an under-explored model for the molecular analysis of HATs, BRDs, and HDACs. Studies of HATs, BRDs, and HDACs in Tetrahymena have the potential to reveal the function of HATs and BRDs relevant to both fundamental eukaryotic biology and to the study of disease mechanisms in parasitic protozoa.
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Affiliation(s)
| | | | | | | | - Jeffrey Fillingham
- Department of Chemistry and Biology, Ryerson University, Toronto, ON, Canada
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10
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Tian M, Mochizuki K, Loidl J. Non-coding RNA Transcription in Tetrahymena Meiotic Nuclei Requires Dedicated Mediator Complex-Associated Proteins. Curr Biol 2019; 29:2359-2370.e5. [PMID: 31280995 DOI: 10.1016/j.cub.2019.05.038] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2019] [Revised: 04/24/2019] [Accepted: 05/15/2019] [Indexed: 12/22/2022]
Abstract
To preserve genome integrity, eukaryotic cells use small RNA-directed mechanisms to repress transposable elements (TEs). Paradoxically, in order to silence TEs, precursors of the small RNAs must be transcribed from TEs. However, it is still poorly understood how these precursors are transcribed from TEs under silenced conditions. In the otherwise transcriptionally silent germline micronucleus (MIC) of Tetrahymena, a burst of non-coding RNA (ncRNA) transcription occurs during meiosis. The transcripts are processed into small RNAs that serve to identify TE-related sequences for elimination. The Mediator complex (Med) has an evolutionarily conserved role for transcription by bridging gene-specific transcription factors and RNA polymerase II. Here, we report that three Med-associated factors, Emit1, Emit2, and Rib1, are required for the biogenesis of small ncRNAs. Med localizes to the MIC only during meiosis, and both Med localization and MIC ncRNA transcription require Emit1 and Emit2. In the MIC, Med occupies TE-rich pericentromeric and telomeric regions in a Rib1-dependent manner. Rib1 is dispensable for ncRNA transcription but is required for the accumulation of double-stranded ncRNAs. Nuclear and sub-nuclear localization of the three Med-associated proteins is interdependent. Hence, Emit1 and Emit2 act coordinately to import Med into the MIC, and Rib1 recruits Med to specific chromosomal locations to quantitatively or qualitatively promote the biogenesis of functional ncRNA. Our results underscore that the transcription machinery can be regulated by a set of specialized Med-associated proteins to temporally transcribe TE-related sequences from a silent genome for small RNA biogenesis and genome defense.
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Affiliation(s)
- Miao Tian
- Department of Chromosome Biology, Max F. Perutz Laboratories, University of Vienna, 1030 Vienna, Austria.
| | - Kazufumi Mochizuki
- Institute of Human Genetics (IGH), CNRS, University of Montpellier, 34090 Montpellier, France
| | - Josef Loidl
- Department of Chromosome Biology, Max F. Perutz Laboratories, University of Vienna, 1030 Vienna, Austria
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11
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Tian M, Loidl J. A chromatin-associated protein required for inducing and limiting meiotic DNA double-strand break formation. Nucleic Acids Res 2019; 46:11822-11834. [PMID: 30357385 PMCID: PMC6294514 DOI: 10.1093/nar/gky968] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2018] [Accepted: 10/05/2018] [Indexed: 11/13/2022] Open
Abstract
Programmed DNA double-strand breaks (DSBs) are required for meiotic recombination, but the number is strictly controlled because they are potentially harmful. Here we report a novel protein, Pars11, which is required for Spo11-dependent DSB formation in the protist Tetrahymena. Pars11 localizes to chromatin early in meiotic prophase in a Spo11-independent manner and is removed before the end of prophase. Pars11 removal depends on DSB formation and ATR-dependent phosphorylation. In the absence of the DNA damage sensor kinase ATR, Pars11 is retained on chromatin and excess DSBs are generated. Similar levels of Pars11 persistence and DSB overproduction occur in a non-phosphorylatable pars11 mutant. We conclude that Pars11 supports DSB formation by Spo11 until enough DSBs are formed; thereafter, DSB production stops in response to ATR-dependent degradation of Pars11 or its removal from chromatin. A similar DSB control mechanism involving a Rec114-Tel1/ATM-dependent negative feedback loop regulates DSB formation in budding yeast. However, there is no detectable sequence homology between Pars11 and Rec114, and DSB numbers are more tightly controlled by Pars11 than by Rec114. The discovery of this mechanism for DSB regulation in the evolutionarily distant protist and fungal lineages suggests that it is conserved across eukaryotes.
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Affiliation(s)
- Miao Tian
- Department of Chromosome Biology, Max F. Perutz Laboratories, University of Vienna, 1030 Vienna, Austria
| | - Josef Loidl
- Department of Chromosome Biology, Max F. Perutz Laboratories, University of Vienna, 1030 Vienna, Austria
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12
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Xu J, Li X, Song W, Wang W, Gao S. Cyclin Cyc2p is required for micronuclear bouquet formation in Tetrahymena thermophila. SCIENCE CHINA-LIFE SCIENCES 2019; 62:668-680. [PMID: 30820856 DOI: 10.1007/s11427-018-9369-3] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/18/2018] [Accepted: 11/19/2018] [Indexed: 01/31/2023]
Abstract
Meiotic bouquet formation (known as crescent formation in Tetrahymena thermophila) is indispensable for homologous pairing and recombination, but the regulatory mechanism of bouquet formation remains largely unknown. As a conjugation specific cyclin gene, CYC2 knockout mutants failed to form an elongated crescent structure and aborted meiosis progress in T. thermophila. γ-H2A.X staining revealed fewer micronuclear DNA double-strand breaks (DSBs) in cyc2Δ cells than in wild-type cells. Furthermore, cyc2Δ cells still failed to form a crescent structure even though DSBs were induced by exogenous agents, indicating that a lack of DSBs was not completely responsible for failure to enter the crescent stage. Tubulin staining showed that impaired perinuclear microtubule structure may contribute to the blockage in micronuclear elongation. At the same time, expression of microtubule-associated kinesin genes, KIN11 and KIN141, was significantly downregulated in cyc2Δ cells. Moreover, micronuclear specific accumulation of heterochromatin marker trimethylated H3K23 abnormally increased in the cyc2Δ mutants. Together, these results show that cyclin Cyc2p is required for micronuclear bouquet formation via controlling microtubule-directed nuclear elongation in Tetrahymena.
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Affiliation(s)
- Jing Xu
- Institute of Evolution & Marine Biodiversity, Ocean University of China, Qingdao, 266003, China
- College of Life Science, Shanxi University, Taiyuan, 030006, China
- Key Laboratory of Chemical Biology and Molecular Engineering of the Ministry of Education, Institute of Biotechnology, Shanxi University, Taiyuan, 030006, China
| | - Xiaoxiong Li
- Key Laboratory of Chemical Biology and Molecular Engineering of the Ministry of Education, Institute of Biotechnology, Shanxi University, Taiyuan, 030006, China
| | - Weibo Song
- Institute of Evolution & Marine Biodiversity, Ocean University of China, Qingdao, 266003, China
- Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao, 266003, China
| | - Wei Wang
- Key Laboratory of Chemical Biology and Molecular Engineering of the Ministry of Education, Institute of Biotechnology, Shanxi University, Taiyuan, 030006, China.
| | - Shan Gao
- Institute of Evolution & Marine Biodiversity, Ocean University of China, Qingdao, 266003, China.
- Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao, 266003, China.
- College of Marine Life Sciences, Ocean University of China, Qingdao, 266003, China.
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13
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Noto T, Mochizuki K. Whats, hows and whys of programmed DNA elimination in Tetrahymena. Open Biol 2018; 7:rsob.170172. [PMID: 29021213 PMCID: PMC5666084 DOI: 10.1098/rsob.170172] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2017] [Accepted: 09/12/2017] [Indexed: 12/20/2022] Open
Abstract
Programmed genome rearrangements in ciliates provide fascinating examples of flexible epigenetic genome regulations and important insights into the interaction between transposable elements (TEs) and host genomes. DNA elimination in Tetrahymena thermophila removes approximately 12 000 internal eliminated sequences (IESs), which correspond to one-third of the genome, when the somatic macronucleus (MAC) differentiates from the germline micronucleus (MIC). More than half of the IESs, many of which show high similarity to TEs, are targeted for elimination in cis by the small RNA-mediated genome comparison of the MIC to the MAC. Other IESs are targeted for elimination in trans by the same small RNAs through repetitive sequences. Furthermore, the small RNA–heterochromatin feedback loop ensures robust DNA elimination. Here, we review an updated picture of the DNA elimination mechanism, discuss the physiological and evolutionary roles of DNA elimination, and outline the key questions that remain unanswered.
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Affiliation(s)
- Tomoko Noto
- Institute of Human Genetics, UMR 9002, CNRS and University of Montpellier, Montpellier, France
| | - Kazufumi Mochizuki
- Institute of Human Genetics, UMR 9002, CNRS and University of Montpellier, Montpellier, France
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14
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Feng L, Wang G, Hamilton EP, Xiong J, Yan G, Chen K, Chen X, Dui W, Plemens A, Khadr L, Dhanekula A, Juma M, Dang HQ, Kapler GM, Orias E, Miao W, Liu Y. A germline-limited piggyBac transposase gene is required for precise excision in Tetrahymena genome rearrangement. Nucleic Acids Res 2017; 45:9481-9502. [PMID: 28934495 PMCID: PMC5766162 DOI: 10.1093/nar/gkx652] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2017] [Accepted: 07/15/2017] [Indexed: 12/20/2022] Open
Abstract
Developmentally programmed genome rearrangement accompanies differentiation of the silent germline micronucleus into the transcriptionally active somatic macronucleus in the ciliated protozoan Tetrahymena thermophila. Internal eliminated sequences (IES) are excised, followed by rejoining of MAC-destined sequences, while fragmentation occurs at conserved chromosome breakage sequences, generating macronuclear chromosomes. Some macronuclear chromosomes, referred to as non-maintained chromosomes (NMC), are lost soon after differentiation. Large NMC contain genes implicated in development-specific roles. One such gene encodes the domesticated piggyBac transposase TPB6, required for heterochromatin-dependent precise excision of IES residing within exons of functionally important genes. These conserved exonic IES determine alternative transcription products in the developing macronucleus; some even contain free-standing genes. Examples of precise loss of some exonic IES in the micronucleus and retention of others in the macronucleus of related species suggest an evolutionary analogy to introns. Our results reveal that germline-limited sequences can encode genes with specific expression patterns and development-related functions, which may be a recurring theme in eukaryotic organisms experiencing programmed genome rearrangement during germline to soma differentiation.
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Affiliation(s)
- Lifang Feng
- Department of Pathology, University of Michigan, Ann Arbor, MI 48109, USA.,Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China.,School of Food Science and Biotechnology, Zhejiang Gongshang University, Hangzhou 310018, China
| | - Guangying Wang
- Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China
| | - Eileen P Hamilton
- Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, CA 93106, USA
| | - Jie Xiong
- Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China
| | - Guanxiong Yan
- Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China
| | - Kai Chen
- Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China
| | - Xiao Chen
- Department of Pathology, University of Michigan, Ann Arbor, MI 48109, USA
| | - Wen Dui
- Department of Pathology, University of Michigan, Ann Arbor, MI 48109, USA
| | - Amber Plemens
- Department of Pathology, University of Michigan, Ann Arbor, MI 48109, USA
| | - Lara Khadr
- Department of Pathology, University of Michigan, Ann Arbor, MI 48109, USA
| | - Arjune Dhanekula
- Department of Pathology, University of Michigan, Ann Arbor, MI 48109, USA
| | - Mina Juma
- Department of Pathology, University of Michigan, Ann Arbor, MI 48109, USA
| | - Hung Quang Dang
- Department of Molecular and Cellular Medicine, Texas A&M University Health Science Center, College Station, TX 77843, USA
| | - Geoffrey M Kapler
- Department of Molecular and Cellular Medicine, Texas A&M University Health Science Center, College Station, TX 77843, USA
| | - Eduardo Orias
- Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, CA 93106, USA
| | - Wei Miao
- Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China
| | - Yifan Liu
- Department of Pathology, University of Michigan, Ann Arbor, MI 48109, USA
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15
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Wang Y, Wang Y, Sheng Y, Huang J, Chen X, AL-Rasheid KA, Gao S. A comparative study of genome organization and epigenetic mechanisms in model ciliates, with an emphasis on Tetrahymena , Paramecium and Oxytricha. Eur J Protistol 2017; 61:376-387. [DOI: 10.1016/j.ejop.2017.06.006] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2016] [Revised: 06/20/2017] [Accepted: 06/20/2017] [Indexed: 10/19/2022]
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16
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van Hooff JJ, Tromer E, van Wijk LM, Snel B, Kops GJ. Evolutionary dynamics of the kinetochore network in eukaryotes as revealed by comparative genomics. EMBO Rep 2017. [PMID: 28642229 PMCID: PMC5579357 DOI: 10.15252/embr.201744102] [Citation(s) in RCA: 132] [Impact Index Per Article: 18.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
During eukaryotic cell division, the sister chromatids of duplicated chromosomes are pulled apart by microtubules, which connect via kinetochores. The kinetochore is a multiprotein structure that links centromeres to microtubules, and that emits molecular signals in order to safeguard the equal distribution of duplicated chromosomes over daughter cells. Although microtubule‐mediated chromosome segregation is evolutionary conserved, kinetochore compositions seem to have diverged. To systematically inventory kinetochore diversity and to reconstruct its evolution, we determined orthologs of 70 kinetochore proteins in 90 phylogenetically diverse eukaryotes. The resulting ortholog sets imply that the last eukaryotic common ancestor (LECA) possessed a complex kinetochore and highlight that current‐day kinetochores differ substantially. These kinetochores diverged through gene loss, duplication, and, less frequently, invention and displacement. Various kinetochore components co‐evolved with one another, albeit in different manners. These co‐evolutionary patterns improve our understanding of kinetochore function and evolution, which we illustrated with the RZZ complex, TRIP13, the MCC, and some nuclear pore proteins. The extensive diversity of kinetochore compositions in eukaryotes poses numerous questions regarding evolutionary flexibility of essential cellular functions.
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Affiliation(s)
- Jolien Je van Hooff
- Hubrecht Institute - KNAW (Royal Netherlands Academy of Arts and Sciences), Utrecht, The Netherlands.,Theoretical Biology and Bioinformatics, Department of Biology, Science Faculty, Utrecht University, Utrecht, The Netherlands.,Molecular Cancer Research, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Eelco Tromer
- Hubrecht Institute - KNAW (Royal Netherlands Academy of Arts and Sciences), Utrecht, The Netherlands.,Theoretical Biology and Bioinformatics, Department of Biology, Science Faculty, Utrecht University, Utrecht, The Netherlands
| | - Leny M van Wijk
- Theoretical Biology and Bioinformatics, Department of Biology, Science Faculty, Utrecht University, Utrecht, The Netherlands
| | - Berend Snel
- Theoretical Biology and Bioinformatics, Department of Biology, Science Faculty, Utrecht University, Utrecht, The Netherlands
| | - Geert Jpl Kops
- Hubrecht Institute - KNAW (Royal Netherlands Academy of Arts and Sciences), Utrecht, The Netherlands .,Molecular Cancer Research, University Medical Center Utrecht, Utrecht, The Netherlands.,Cancer Genomics Netherlands, University Medical Center Utrecht, Utrecht, The Netherlands
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17
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Evolutionary Lessons from Species with Unique Kinetochores. CENTROMERES AND KINETOCHORES 2017; 56:111-138. [DOI: 10.1007/978-3-319-58592-5_5] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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18
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McDaniel SL, Zweifel E, Harris PKW, Yao MC, Cole ES, Chalker DL. DRH1, a p68-related RNA helicase gene, is required for chromosome breakage in Tetrahymena. Biol Open 2016; 5:1790-1798. [PMID: 27793833 PMCID: PMC5200911 DOI: 10.1242/bio.021576] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The p68 DEAD box helicases comprise a widely conserved protein family involved in a large range of biological processes including transcription, splicing and translation. The genome of the ciliate Tetrahymena thermophile encodes two p68-like helicases, Drh1p and Lia2p. We show that DRH1 is essential for growth and completion of development. In growing cells, Drh1p is excluded from the nucleus and accumulates near cortical basal bodies. In contrast, during sexual reproduction, this protein localizes to meiotic micronuclei, initially in punctate foci in regions where centromeres and telomeres are known to reside and later in post-zygotic differentiating somatic macronuclei. Differentiation of the macronuclear genome involves extensive DNA rearrangements including fragmentation of the five pairs of germline-derived chromosomes into 180 chromosomal sub-fragments that are stabilized by de novo telomere deletion. In addition, thousands of internal eliminated sequences (IESs) are excised from loci dispersed throughout the genome. Strains with DRH1 deleted from the germline nuclei, which do not express the protein during post-zygotic development, fail to fragment the developing macronuclear chromosomes. IES excision still occurs in the absence of DRH1 zygotic expression; thus, Drh1p is the first protein found to be specifically required for chromosome breakage but not DNA elimination. Summary: The p68-related Drh1protein is essential for both growth and development of the ciliate Tetrahymena thermophila. It localizes to meiotic nuclei and is required for chromosome breakage of developing somatic chromosomes.
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Affiliation(s)
- Stephen L McDaniel
- Department of Biology, Washington University in St. Louis, St Louis, MO 63130, USA
| | - Erica Zweifel
- Biology Department, St. Olaf College, 1520 St. Olaf Avenue, Northfield, MN 55057, USA
| | - Peter K W Harris
- Department of Biology, Washington University in St. Louis, St Louis, MO 63130, USA
| | - Meng-Chao Yao
- Institute of Molecular Biology, Academia Sinica, Nankang, Taipei 11529, Taiwan
| | - Eric S Cole
- Biology Department, St. Olaf College, 1520 St. Olaf Avenue, Northfield, MN 55057, USA
| | - Douglas L Chalker
- Department of Biology, Washington University in St. Louis, St Louis, MO 63130, USA
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19
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Hamilton EP, Kapusta A, Huvos PE, Bidwell SL, Zafar N, Tang H, Hadjithomas M, Krishnakumar V, Badger JH, Caler EV, Russ C, Zeng Q, Fan L, Levin JZ, Shea T, Young SK, Hegarty R, Daza R, Gujja S, Wortman JR, Birren BW, Nusbaum C, Thomas J, Carey CM, Pritham EJ, Feschotte C, Noto T, Mochizuki K, Papazyan R, Taverna SD, Dear PH, Cassidy-Hanley DM, Xiong J, Miao W, Orias E, Coyne RS. Structure of the germline genome of Tetrahymena thermophila and relationship to the massively rearranged somatic genome. eLife 2016; 5. [PMID: 27892853 PMCID: PMC5182062 DOI: 10.7554/elife.19090] [Citation(s) in RCA: 108] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2016] [Accepted: 11/14/2016] [Indexed: 12/30/2022] Open
Abstract
The germline genome of the binucleated ciliate Tetrahymena thermophila undergoes programmed chromosome breakage and massive DNA elimination to generate the somatic genome. Here, we present a complete sequence assembly of the germline genome and analyze multiple features of its structure and its relationship to the somatic genome, shedding light on the mechanisms of genome rearrangement as well as the evolutionary history of this remarkable germline/soma differentiation. Our results strengthen the notion that a complex, dynamic, and ongoing interplay between mobile DNA elements and the host genome have shaped Tetrahymena chromosome structure, locally and globally. Non-standard outcomes of rearrangement events, including the generation of short-lived somatic chromosomes and excision of DNA interrupting protein-coding regions, may represent novel forms of developmental gene regulation. We also compare Tetrahymena's germline/soma differentiation to that of other characterized ciliates, illustrating the wide diversity of adaptations that have occurred within this phylum.
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Affiliation(s)
- Eileen P Hamilton
- Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, Santa Barbara, United States
| | - Aurélie Kapusta
- Department of Human Genetics, University of Utah School of Medicine, Salt Lake City, United States
| | - Piroska E Huvos
- Biochemistry and Molecular Biology, Southern Illinois University, Carbondale, United States
| | | | - Nikhat Zafar
- J. Craig Venter Institute, Rockville, United States
| | - Haibao Tang
- J. Craig Venter Institute, Rockville, United States
| | | | | | | | | | - Carsten Russ
- Eli and Edythe L. Broad Institute of Harvard and MIT, Cambridge, United States
| | - Qiandong Zeng
- Eli and Edythe L. Broad Institute of Harvard and MIT, Cambridge, United States
| | - Lin Fan
- Eli and Edythe L. Broad Institute of Harvard and MIT, Cambridge, United States
| | - Joshua Z Levin
- Eli and Edythe L. Broad Institute of Harvard and MIT, Cambridge, United States
| | - Terrance Shea
- Eli and Edythe L. Broad Institute of Harvard and MIT, Cambridge, United States
| | - Sarah K Young
- Eli and Edythe L. Broad Institute of Harvard and MIT, Cambridge, United States
| | - Ryan Hegarty
- Eli and Edythe L. Broad Institute of Harvard and MIT, Cambridge, United States
| | - Riza Daza
- Eli and Edythe L. Broad Institute of Harvard and MIT, Cambridge, United States
| | - Sharvari Gujja
- Eli and Edythe L. Broad Institute of Harvard and MIT, Cambridge, United States
| | - Jennifer R Wortman
- Eli and Edythe L. Broad Institute of Harvard and MIT, Cambridge, United States
| | - Bruce W Birren
- Eli and Edythe L. Broad Institute of Harvard and MIT, Cambridge, United States
| | - Chad Nusbaum
- Eli and Edythe L. Broad Institute of Harvard and MIT, Cambridge, United States
| | - Jainy Thomas
- Department of Human Genetics, University of Utah School of Medicine, Salt Lake City, United States
| | - Clayton M Carey
- Department of Human Genetics, University of Utah School of Medicine, Salt Lake City, United States
| | - Ellen J Pritham
- Department of Human Genetics, University of Utah School of Medicine, Salt Lake City, United States
| | - Cédric Feschotte
- Department of Human Genetics, University of Utah School of Medicine, Salt Lake City, United States
| | - Tomoko Noto
- Institute of Molecular Biotechnology, Vienna, Austria
| | | | - Romeo Papazyan
- Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, Baltimore, United States
| | - Sean D Taverna
- Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, Baltimore, United States
| | - Paul H Dear
- MRC Laboratory of Molecular Biology, Cambridge, United Kingdom
| | | | - Jie Xiong
- Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, China
| | - Wei Miao
- Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, China
| | - Eduardo Orias
- Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, Santa Barbara, United States
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20
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Kushida Y, Takaine M, Nakano K, Sugai T, Vasudevan KK, Guha M, Jiang YY, Gaertig J, Numata O. Kinesin-14 is Important for Chromosome Segregation During Mitosis and Meiosis in the Ciliate Tetrahymena thermophila. J Eukaryot Microbiol 2016; 64:293-307. [PMID: 27595611 DOI: 10.1111/jeu.12366] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2016] [Revised: 08/26/2016] [Accepted: 08/30/2016] [Indexed: 11/29/2022]
Abstract
Ciliates such as Tetrahymena thermophila have two distinct nuclei within one cell: the micronucleus that undergoes mitosis and meiosis and the macronucleus that undergoes amitosis, a type of nuclear division that does not involve a bipolar spindle, but still relies on intranuclear microtubules. Ciliates provide an opportunity for the discovery of factors that specifically contribute to chromosome segregation based on a bipolar spindle, by identification of factors that affect the micronuclear but not the macronuclear division. Kinesin-14 is a conserved minus-end directed microtubule motor that cross-links microtubules and contributes to the bipolar spindle sizing and organization. Here, we use homologous DNA recombination to knock out genes that encode kinesin-14 orthologues (KIN141, KIN142) in Tetrahymena. A loss of KIN141 led to severe defects in the chromosome segregation during both mitosis and meiosis but did not affect amitosis. A loss of KIN141 altered the shape of the meiotic spindle in a way consistent with the KIN141's contribution to the organization of the spindle poles. EGFP-tagged KIN141 preferentially accumulated at the spindle poles during the meiotic prophase and metaphase I. Thus, in ciliates, kinesin-14 is important for nuclear divisions that involve a bipolar spindle.
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Affiliation(s)
- Yasuharu Kushida
- Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki, 305-8572, Japan.,Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Gunma, 371-8512, Japan
| | - Masak Takaine
- Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki, 305-8572, Japan.,Gunma University Initiative for Advanced Research, Gunma University, Maebashi, Gunma, 371-8511, Japan
| | - Kentaro Nakano
- Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki, 305-8572, Japan
| | - Toshiro Sugai
- Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki, 305-8572, Japan
| | | | - Mayukh Guha
- Department of Cellular Biology, University of Georgia, Athens, Georgia, 30602, USA
| | - Yu-Yang Jiang
- Department of Cellular Biology, University of Georgia, Athens, Georgia, 30602, USA
| | - Jacek Gaertig
- Department of Cellular Biology, University of Georgia, Athens, Georgia, 30602, USA
| | - Osamu Numata
- Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki, 305-8572, Japan
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21
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Yan GX, Dang H, Tian M, Zhang J, Shodhan A, Ning YZ, Xiong J, Miao W. Cyc17, a meiosis-specific cyclin, is essential for anaphase initiation and chromosome segregation in Tetrahymena thermophila. Cell Cycle 2016; 15:1855-64. [PMID: 27192402 DOI: 10.1080/15384101.2016.1188238] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Although the role of cyclins in controlling nuclear division is well established, their function in ciliate meiosis remains unknown. In ciliates, the cyclin family has undergone massive expansion which suggests that diverse cell cycle systems exist, and this warrants further investigation. A screen for cyclins in the model ciliate Tetrahymena thermophila showed that there are 34 cyclins in this organism. Only 1 cyclin, Cyc17, contains the complete cyclin core and is specifically expressed during meiosis. Deletion of CYC17 led to meiotic arrest at the diakinesis-like metaphase I stage. Expression of genes involved in DNA metabolism and chromosome organization (chromatin remodeling and basic chromosomal structure) was repressed in cyc17 knockout matings. Further investigation suggested that Cyc17 is involved in regulating spindle pole attachment, and is thus essential for chromosome segregation at meiosis. These findings suggest a simple model in which chromosome segregation is influenced by Cyc17.
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Affiliation(s)
- Guan-Xiong Yan
- a Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences , Wuhan , People's Republic of China.,b University of Chinese Academy of Sciences , Beijing , People's Republic of China
| | - Huai Dang
- c College of Life Sciences, Northwest Normal University , Lanzhou , People's Republic of China
| | - Miao Tian
- a Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences , Wuhan , People's Republic of China.,d Department of Chromosome Biology and Max F. Perutz Laboratories , Center for Molecular Biology, University of Vienna , Vienna , Austria
| | - Jing Zhang
- a Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences , Wuhan , People's Republic of China.,b University of Chinese Academy of Sciences , Beijing , People's Republic of China
| | - Anura Shodhan
- d Department of Chromosome Biology and Max F. Perutz Laboratories , Center for Molecular Biology, University of Vienna , Vienna , Austria
| | - Ying-Zhi Ning
- c College of Life Sciences, Northwest Normal University , Lanzhou , People's Republic of China
| | - Jie Xiong
- a Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences , Wuhan , People's Republic of China
| | - Wei Miao
- a Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences , Wuhan , People's Republic of China
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22
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Lhuillier-Akakpo M, Guérin F, Frapporti A, Duharcourt S. DNA deletion as a mechanism for developmentally programmed centromere loss. Nucleic Acids Res 2015; 44:1553-65. [PMID: 26503246 PMCID: PMC4770206 DOI: 10.1093/nar/gkv1110] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2015] [Accepted: 10/12/2015] [Indexed: 12/31/2022] Open
Abstract
A hallmark of active centromeres is the presence of the histone H3 variant CenH3 in the centromeric chromatin, which ensures faithful genome distribution at each cell division. A functional centromere can be inactivated, but the molecular mechanisms underlying the process of centromere inactivation remain largely unknown. Here, we describe the loss of CenH3 protein as part of a developmental program leading to the formation of the somatic nucleus in the eukaryote Paramecium. We identify two proteins whose depletion prevents developmental loss of CenH3: the domesticated transposase Pgm involved in the formation of DNA double strand cleavages and the Polycomb-like lysine methyltransferase Ezl1 necessary for trimethylation of histone H3 on lysine 9 and lysine 27. Taken together, our data support a model in which developmentally programmed centromere loss is caused by the elimination of DNA sequences associated with CenH3.
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Affiliation(s)
- Maoussi Lhuillier-Akakpo
- Institut Jacques Monod, CNRS, UMR 7592, Université Paris Diderot, Sorbonne Paris Cité, Paris, F-75205 France
| | - Frédéric Guérin
- Institut Jacques Monod, CNRS, UMR 7592, Université Paris Diderot, Sorbonne Paris Cité, Paris, F-75205 France
| | - Andrea Frapporti
- Institut Jacques Monod, CNRS, UMR 7592, Université Paris Diderot, Sorbonne Paris Cité, Paris, F-75205 France
| | - Sandra Duharcourt
- Institut Jacques Monod, CNRS, UMR 7592, Université Paris Diderot, Sorbonne Paris Cité, Paris, F-75205 France
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23
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Papazyan R, Voronina E, Chapman JR, Luperchio TR, Gilbert TM, Meier E, Mackintosh SG, Shabanowitz J, Tackett AJ, Reddy KL, Coyne RS, Hunt DF, Liu Y, Taverna SD. Methylation of histone H3K23 blocks DNA damage in pericentric heterochromatin during meiosis. eLife 2014; 3:e02996. [PMID: 25161194 PMCID: PMC4141274 DOI: 10.7554/elife.02996] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Despite the well-established role of heterochromatin in protecting chromosomal integrity during meiosis and mitosis, the contribution and extent of heterochromatic histone posttranslational modifications (PTMs) remain poorly defined. Here, we gained novel functional insight about heterochromatic PTMs by analyzing histone H3 purified from the heterochromatic germline micronucleus of the model organism Tetrahymena thermophila. Mass spectrometric sequencing of micronuclear H3 identified H3K23 trimethylation (H3K23me3), a previously uncharacterized PTM. H3K23me3 became particularly enriched during meiotic leptotene and zygotene in germline chromatin of Tetrahymena and C. elegans. Loss of H3K23me3 in Tetrahymena through deletion of the methyltransferase Ezl3p caused mislocalization of meiosis-induced DNA double-strand breaks (DSBs) to heterochromatin, and a decrease in progeny viability. These results show that an evolutionarily conserved developmental pathway regulates H3K23me3 during meiosis, and our studies in Tetrahymena suggest this pathway may function to protect heterochromatin from DSBs. DOI:http://dx.doi.org/10.7554/eLife.02996.001 Inside the nucleus of a cell, the DNA is wound around histone proteins. This forms a structure called chromatin that allows the long DNA strands to fit inside the cell. Variations in chromatin structure also help the cell to control the functional properties of DNA. For example, a large proportion of chromatin in the cell is in the form of heterochromatin, which is very densely packed, and is associated with many roles such as gene silencing and keeping DNA intact during reproduction. Many animals and plants have two copies of each DNA molecule: one inherited from the mother, and one from the father of the organism. Reproductive cells undergo a process called recombination when they form, where the matching copies of each DNA molecule break in a number of places and rejoin to form a new ‘blend’ of their mother's and their father's DNA, which is passed on to their own offspring. In contrast, most heterochromatin is inherited without recombining, preserving it in an unaltered form. This is important since recombination in heterochromatin can create genetic abnormalities. Adding small chemical modifications—such as methyl groups—to the histone proteins at the core of the chromatin can change how the DNA is packed. However, the histone modifications that yield different chromatin structures, and the effect of these modifications, are not very well understood. Papazyan et al. have taken advantage of a distinct feature of the protozoan Tetrahymena thermophila: a single-celled organism that divides its chromatin into two different nuclei. The smaller micronuclei contain only heterochromatin, and Papazyan et al. discovered that the histone H3 protein in the micronuclei is modified by methyl groups at a specific site that had not been studied before. Furthermore, this protozoan makes more of these modifications when it reproduces. An enzyme called Ezl3p adds these methyl groups, and without this enzyme T. thermophila reproduces more slowly and has offspring that are less likely to survive and more likely to be infertile. Papazyan et al. provide evidence that these characteristics arise because the cells without the histone modification are unable to prevent DNA breaks from occurring in heterochromatin during recombination. The same histone modification also occurs when the microscopic worm Caenorhabditis elegans reproduces, suggesting that this method of DNA protection has been conserved throughout evolution. Papazyan et al. propose that the histone modification may prevent another enzyme that induces DNA breaks from accessing the heterochromatin in reproductive cells; but more work is required to support this hypothesis. These findings reveal the importance of a new histone modification during reproduction, and could provide new directions for infertility research. DOI:http://dx.doi.org/10.7554/eLife.02996.002
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Affiliation(s)
- Romeo Papazyan
- Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, Baltimore, United States Center for Epigenetics, The Johns Hopkins University School of Medicine, Baltimore, United States
| | - Ekaterina Voronina
- Department of Molecular Biology and Genetics, Howard Hughes Medical Institute, The Johns Hopkins University School of Medicine, Balitmore, United States Center for Cell Dynamics, The Johns Hopkins University School of Medicine, Baltimore, United States
| | - Jessica R Chapman
- Department of Chemistry, University of Virginia, Charlottesville, United States
| | - Teresa R Luperchio
- Center for Epigenetics, The Johns Hopkins University School of Medicine, Baltimore, United States Department of Biological Chemistry, The Johns Hopkins University School of Medicine, Baltimore, United States
| | - Tonya M Gilbert
- Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, Baltimore, United States Center for Epigenetics, The Johns Hopkins University School of Medicine, Baltimore, United States
| | - Elizabeth Meier
- Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, Baltimore, United States Center for Epigenetics, The Johns Hopkins University School of Medicine, Baltimore, United States
| | - Samuel G Mackintosh
- Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, United States
| | - Jeffrey Shabanowitz
- Department of Chemistry, University of Virginia, Charlottesville, United States
| | - Alan J Tackett
- Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, United States
| | - Karen L Reddy
- Center for Epigenetics, The Johns Hopkins University School of Medicine, Baltimore, United States Department of Biological Chemistry, The Johns Hopkins University School of Medicine, Baltimore, United States
| | - Robert S Coyne
- Department of Genomic Medicine, J. Craig Venter Institute, Rockville, United States
| | - Donald F Hunt
- Department of Chemistry, University of Virginia, Charlottesville, United States Department of Pathology, University of Virginia, Charlottesville, United States
| | - Yifan Liu
- Department of Pathology, University of Michigan Medical School, Ann Arbor, United States
| | - Sean D Taverna
- Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, Baltimore, United States Center for Epigenetics, The Johns Hopkins University School of Medicine, Baltimore, United States
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24
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Abstract
Research using ciliates revealed early examples of epigenetic phenomena and continues to provide novel findings. These protozoans maintain separate germline and somatic nuclei that carry transcriptionally silent and active genomes, respectively. Examining the differences in chromatin within distinct nuclei of Tetrahymena identified histone variants and established that transcriptional regulators act by modifying histones. Formation of somatic nuclei requires both transcriptional activation of silent chromatin and large-scale DNA elimination. This somatic genome remodeling is directed by homologous RNAs, acting with an RNA interference (RNAi)-related machinery. Furthermore, the content of the parental somatic genome provides a homologous template to guide this genome restructuring. The mechanisms regulating ciliate DNA rearrangements reveal the surprising power of homologous RNAs to remodel the genome and transmit information transgenerationally.
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Affiliation(s)
- Douglas L Chalker
- Department of Biology, Washington University, St. Louis, Missouri 63130
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25
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Lukaszewicz A, Howard-Till RA, Loidl J. Mus81 nuclease and Sgs1 helicase are essential for meiotic recombination in a protist lacking a synaptonemal complex. Nucleic Acids Res 2013; 41:9296-309. [PMID: 23935123 PMCID: PMC3814389 DOI: 10.1093/nar/gkt703] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2013] [Revised: 07/17/2013] [Accepted: 07/18/2013] [Indexed: 11/18/2022] Open
Abstract
Mus81 resolvase and Sgs1 helicase have well-established roles in mitotic DNA repair. Moreover, Mus81 is part of a minor crossover (CO) pathway in the meiosis of budding yeast, plants and vertebrates. The major pathway depends on meiosis-specific synaptonemal complex (SC) formation, ZMM proteins and the MutLγ complex for CO-directed resolution of joint molecule (JM)-recombination intermediates. Sgs1 has also been implicated in this pathway, although it may mainly promote the non-CO outcome of meiotic repair. We show in Tetrahymena, that homologous chromosomes fail to separate and JMs accumulate in the absence of Mus81 or Sgs1, whereas deletion of the MutLγ-component Mlh1 does not affect meiotic divisions. Thus, our results are consistent with Mus81 being part of an essential, if not the predominant, CO pathway in Tetrahymena. Sgs1 may exert functions similar to those in other eukaryotes. However, we propose an additional role in supporting homologous CO formation by promoting homologous over intersister interactions. Tetrahymena shares the predominance of the Mus81 CO pathway with the fission yeast. We propose that in these two organisms, which independently lost the SC during evolution, the basal set of mitotic repair proteins is sufficient for executing meiotic recombination.
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Affiliation(s)
| | | | - Josef Loidl
- Department of Chromosome Biology, Max F. Perutz Laboratories, Center for Molecular Biology, University of Vienna, A-1030 Vienna, Austria
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26
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Loidl J, Lukaszewicz A, Howard-Till RA, Koestler T. The Tetrahymena meiotic chromosome bouquet is organized by centromeres and promotes interhomolog recombination. J Cell Sci 2012; 125:5873-80. [PMID: 22976299 DOI: 10.1242/jcs.112664] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In order to form crossovers and to undergo reductional segregation during meiosis, homologous chromosomes must pair. In Tetrahymena, meiotic prophase nuclei elongate immensely, and, within the elongated nucleus, chromosomes are arranged with telomeres assembled at one pole and centromeres at the opposite pole. This organisation is an exaggerated form of the bouquet, a meiotic chromosome arrangement that is widely conserved among eukaryotes. We show that centromere function is crucial for the formation of Tetrahymena's stretched bouquet and, thereby, for homologue pairing. This finding adds to previous reports of the importance of centromeres in chromosome pairing in budding yeast and in Drosophila. Tetrahymena's bouquet is an ataxia telangiectasia- and RAD3-related (ATR)-dependent meiotic DNA damage response that is triggered by meiotic DNA double-strand breaks (DSBs), suggesting that the bouquet is needed for DSB repair. However, in the present study we show that although homologous pairing is impeded in the absence of the bouquet, DSB repair takes place nevertheless. Moreover, recombinational DSB repair, as monitored by bromodeoxyuridine incorporation, takes place only after exit from the bouquet stage. Therefore, we conclude that the bouquet is not required for DSB repair per se, but may be necessary for the alignment of homologous loci in order to promote homologous crossovers over alternative repair pathways.
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Affiliation(s)
- Josef Loidl
- Department of Chromosome Biology and Max F. Perutz Laboratories, Center for Molecular Biology, University of Vienna, A-1030 Vienna, Austria
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27
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Coyne RS, Lhuillier-Akakpo M, Duharcourt S. RNA-guided DNA rearrangements in ciliates: is the best genome defence a good offence? Biol Cell 2012; 104:309-25. [PMID: 22352444 DOI: 10.1111/boc.201100057] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2011] [Accepted: 02/15/2012] [Indexed: 12/13/2022]
Abstract
Genomes, like crazy patchwork quilts, are stitched together over evolutionary time from diverse elements, including some unwelcome invaders. To deal with parasitic mobile elements, most eukaryotes employ a genome self-defensive manoeuvre to recognise and silence such elements by homology-dependent interactions with RNA-protein complexes that alter chromatin. Ciliated protozoa employ more 'offensive' tactics by actually unstitching and reassembling their somatic genomes at every sexual generation to eliminate transposons and their remnants, using as patterns the maternal genomes that were rearranged in the previous cycle. Genetic and genomic studies of the distant relatives Paramecium and Tetrahymena have begun to reveal how such events are carried out with remarkable precision. Whole genome, non-coding transcripts from the maternal genome are compared with transcripts from the zygotic genome that are processed through an RNA interference (RNAi)-related process. Sequences found only in the latter are targeted for elimination by the resulting short 'scanRNAs' in many thousand DNA splicing reactions initiated by a domesticated transposase. The involvement of widely conserved mechanisms and protein factors clearly shows the relatedness of these phenomena to RNAi-mediated heterochromatic gene silencing. Such malleability of the genome on a generational time scale also has profound evolutionary implications, possibly including the epigenetic inheritance of acquired adaptive traits.
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28
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Abstract
The parabasalid protist Trichomonas vaginalis is a widespread parasite that affects humans, frequently causing vaginitis in infected women. Trichomonad mitosis is marked by the persistence of the nuclear membrane and the presence of an asymmetric extranuclear spindle with no obvious direct connection to the chromosomes. No centromeric markers have been described in T. vaginalis, which has prevented a detailed analysis of mitotic events in this organism. In other eukaryotes, nucleosomes of centromeric chromatin contain the histone H3 variant CenH3. The principal aim of this work was to identify a CenH3 homolog in T. vaginalis. We performed a screen of the T. vaginalis genome to retrieve sequences of canonical and variant H3 histones. Three variant histone H3 proteins were identified, and the subcellular localization of their epitope-tagged variants was determined. The localization of the variant TVAG_185390 could not be distinguished from that of the canonical H3 histone. The sequence of the variant TVAG_087830 closely resembled that of histone H3. The tagged protein colocalized with sites of active transcription, indicating that the variant TVAG_087830 represented H3.3 in T. vaginalis. The third H3 variant (TVAG_224460) was localized to 6 or 12 distinct spots at the periphery of the nucleus, corresponding to the number of chromosomes in G(1) phase and G(2) phase, respectively. We propose that this variant represents the centromeric marker CenH3 and thus can be employed as a tool to study mitosis in T. vaginalis. Furthermore, we suggest that the peripheral distribution of CenH3 within the nucleus results from the association of centromeres with the nuclear envelope throughout the cell cycle.
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29
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Abstract
Nuclear dualism is a characteristic feature of the ciliated protozoa. Tetrahymena have two different nuclei in each cell. The larger, polyploid, somatic macronucleus (MAC) is the site of transcriptional activity in the vegetatively growing cell. The smaller, diploid micronucleus (MIC) is transcriptionally inactive in vegetative cells, but is transcriptionally active in mating cells and responsible for the genetic continuity during sexual reproduction. Although the MICs and MACs develop from mitotic products of a common progenitor and reside in a common cytoplasm, they are different from one another in almost every respect.
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Affiliation(s)
- Kathleen M Karrer
- Department of Biological Sciences, Marquette University, Milwaukee, Wisconsin, USA
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30
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Wloga D, Frankel J. From Molecules to Morphology: Cellular Organization of Tetrahymena thermophila. Methods Cell Biol 2012; 109:83-140. [DOI: 10.1016/b978-0-12-385967-9.00005-0] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
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31
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Abstract
Within the past decade, genomic studies have emerged as essential and highly productive tools to explore the biology of Tetrahymena thermophila. The current major resources, which have been extensively mined by the research community, are the annotated macronuclear genome assembly, transcriptomic data and the databases that house this information. Efforts in progress will soon improve these data sources and expand their scope, including providing annotated micronuclear and comparative genomic sequences. Future studies of Tetrahymena cell and molecular biology, development, physiology, evolution and ecology will benefit greatly from these resources and the advanced genomic technologies they enable.
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32
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Abstract
The ciliate Tetrahymena thermophila can be said to undergo a variety of developmental programs. During vegetative growth, cells coordinate a variety of cell-cycle operations including macronuclear DNA synthesis and a-mitotic fission, micronuclear DNA synthesis and mitosis, cytokinesis and an elaborate program of cortical morphogenesis that replicates the cortical organelles. When starved, cells undergo oral replacement, transformation into fast-swimming dispersal forms or, when encountering cells of a complementary mating type, conjugation. Conjugation involves a 12 hour program of meiosis, mitosis, nuclear exchange and karyogamy, and two postzygotic divisions of the fertilization nucleus. This chapter reviews experimental data exploring the developmental dependencies associated with both vegetative and conjugal development.
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33
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Motl JA, Chalker DL. Zygotic expression of the double-stranded RNA binding motif protein Drb2p is required for DNA elimination in the ciliate Tetrahymena thermophila. EUKARYOTIC CELL 2011; 10:1648-59. [PMID: 22021239 PMCID: PMC3232721 DOI: 10.1128/ec.05216-11] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/19/2011] [Accepted: 10/13/2011] [Indexed: 11/20/2022]
Abstract
Double-stranded RNA binding motif (DSRM)-containing proteins play many roles in the regulation of gene transcription and translation, including some with tandem DSRMs that act in small RNA biogenesis. We report the characterization of the genes for double-stranded RNA binding proteins 1 and 2 (DRB1 and DRB2), two genes encoding nuclear proteins with tandem DSRMs in the ciliate Tetrahymena thermophila. Both proteins are expressed throughout growth and development but exhibit distinct peaks of expression, suggesting different biological roles. In support of this, we show that expression of DRB2 is essential for vegetative growth while DRB1 expression is not. During conjugation, Drb1p and Drb2p localize to distinct nuclear foci. Cells lacking all DRB1 copies are able to produce viable progeny, although at a reduced rate relative to wild-type cells. In contrast, cells lacking germ line DRB2 copies, which thus cannot express Drb2p zygotically, fail to produce progeny, arresting late into conjugation. This arrest phenotype is accompanied by a failure to organize the essential DNA rearrangement protein Pdd1p into DNA elimination bodies and execute DNA elimination and chromosome breakage. These results implicate zygotically expressed Drb2p in the maturation of these nuclear structures, which are necessary for reorganization of the somatic genome.
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Affiliation(s)
- Jason A. Motl
- Department of Biology, Washington University in St. Louis, Campus Box 1137, One Brookings Dr., St. Louis, Missouri 63130-4899
| | - Douglas L. Chalker
- Department of Biology, Washington University in St. Louis, Campus Box 1137, One Brookings Dr., St. Louis, Missouri 63130-4899
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34
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Mochizuki K. Developmentally programmed, RNA-directed genome rearrangement in Tetrahymena. Dev Growth Differ 2011; 54:108-19. [PMID: 22103557 DOI: 10.1111/j.1440-169x.2011.01305.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Developmentally programmed genome rearrangement has been observed in a variety of eukaryotes from vertebrates to worms to protists, and it provides an interesting exception to the general rule of the constancy of the genome. DNA elimination in the ciliated protozoan Tetrahymena is one of the most well-characterized programmed genome rearrangement events. DNA elimination in the newly formed macronucleus of Tetrahymena is epigenetically regulated by the DNA sequence of the parental macronucleus. Dicer-produced, Piwi-associated small RNAs mediate this epigenetic regulation, probably through a whole-genome comparison of the germline micronucleus to the somatic macronucleus. However, a correlation between small RNAs and programmed genome rearrangement could not be detected in the worm Ascaris suum. Therefore, different types of eukaryotes may have developed unique solutions to perform genome rearrangement.
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Affiliation(s)
- Kazufumi Mochizuki
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), Vienna, Austria.
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35
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Elde NC, Roach KC, Yao MC, Malik HS. Absence of positive selection on centromeric histones in Tetrahymena suggests unsuppressed centromere: drive in lineages lacking male meiosis. J Mol Evol 2011; 72:510-20. [PMID: 21643829 PMCID: PMC3144370 DOI: 10.1007/s00239-011-9449-0] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2011] [Accepted: 05/19/2011] [Indexed: 12/20/2022]
Abstract
Centromere-drive is a process where centromeres compete for transmission through asymmetric "female" meiosis for inclusion into the oocyte. In symmetric "male" meiosis, all meiotic products form viable germ cells. Therefore, the primary incentive for centromere-drive, a potential transmission bias, is believed to be missing from male meiosis. In this article, we consider whether male meiosis also bears the primary cost of centromere-drive. Because different taxa carry out different combinations of meiotic programs (symmetric + asymmetric, symmetric only, asymmetric only), it is possible to consider the evolutionary consequences of centromere-drive in the context of these differing systems. Groups with both types of meiosis have large, rapidly evolving centromeric regions, and their centromeric histones (CenH3s) have been shown to evolve under positive selection, suggesting roles as suppressors of centromere-drive. In contrast, taxa with only symmetric male meiosis have shown no evidence of positive selection in their centromeric histones. In this article, we present the first evolutionary analysis of centromeric histones in ciliated protozoans, a group that only undergoes asymmetric "female" meiosis. We find no evidence of positive selection acting on CNA1, the CenH3 of Tetrahymena species. Cytological observations of a panel of Tetrahymena species are consistent with dynamic karyotype evolution in this lineage. Our findings suggest that defects in male meiosis, and not mitosis or female meiosis, are the primary selective force behind centromere-drive suppression. Our study raises the possibility that taxa like ciliates, with only female meiosis, may therefore undergo unsuppressed centromere drive.
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Affiliation(s)
- Nels C. Elde
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue N. A2-205, Seattle, WA 98109 USA
- Present Address: Department of Human Genetics, University of Utah, Salt Lake City, UT 84112 USA
| | - Kevin C. Roach
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue N. A2-205, Seattle, WA 98109 USA
- Department of Genome Sciences, University of Washington, Seattle, WA 98195 USA
| | - Meng-Chao Yao
- Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan 11529
| | - Harmit S. Malik
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue N. A2-205, Seattle, WA 98109 USA
- HHMI, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue N. A2-205, Seattle, WA 98109 USA
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36
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Kaczanowski A, Kiersnowska M. Inactivation of a macronuclear intra-S-phase checkpoint in Tetrahymena thermophila with caffeine affects the integrity of the micronuclear genome. Protist 2011; 162:616-36. [PMID: 21601521 DOI: 10.1016/j.protis.2011.01.004] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2010] [Accepted: 01/23/2011] [Indexed: 01/16/2023]
Abstract
Aphidicolin (APH), an inhibitor of DNA polymerase α, arrested cell divisions in Tetrahymena thermophila. Surprisingly, low concentrations of APH induced an increase of macronuclear DNA content and cell size in non-dividing cells. In spite of the cell size increase, most proliferation of basal bodies, ciliogenesis and development of new oral primordia were prevented by the APH treatment. The division arrest induced by APH was partly overridden by caffeine (CAF) treatment, which caused the fragmentation ("pulverization") of the chromosomes in G2 micronuclei. Somatic progeny of dividers with pulverized micronuclei (APH+CAF strains) contained aneuploid and amicronucleate cells. The amicronucleate cells, after losing their oral structures and most of their cilia, and undergoing progressive disorganization of cortical structures, assumed an irregular shape ("crinkled") and were nonviable. "Crinkled" cells were not formed after APH + CAF treatment of the amicronuclear BI3840 strain, which contains some mic-specific sequences in its macronucleus. Most of the APH +CAF strains had a typical "*"- like conjugation phenotype: they did not produce pronuclei, but received them unilaterally from their mates and retained old macronuclei. However, 4 among 100 APH+CAF clones induced arrest at meiotic metaphase I in their wt mates. It is likely that the origin of such clones was enhanced by chromosome pulverization.
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37
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Orias E, Cervantes MD, Hamilton EP. Tetrahymena thermophila, a unicellular eukaryote with separate germline and somatic genomes. Res Microbiol 2011; 162:578-86. [PMID: 21624459 DOI: 10.1016/j.resmic.2011.05.001] [Citation(s) in RCA: 82] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2011] [Accepted: 04/14/2011] [Indexed: 12/11/2022]
Abstract
Tetrahymena thermophila is a ciliate--a unicellular eukaryote. Remarkably, every cell maintains differentiated germline and somatic genomes: one silent, the other expressed. Moreover, the two genomes undergo diverse processes, some as extreme as life and death, simultaneously in the same cytoplasm. Conserved eukaryotic mechanisms have been modified in ciliates to selectively deal with the two genomes. We describe research in several areas of Tetrahymena biology, including meiosis, amitosis, genetic assortment, selective nuclear pore transport, somatic RNAi-guided heterochromatin formation, DNA excision and programmed nuclear death by autophagy, which has enriched and broadened knowledge of those mechanisms.
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Affiliation(s)
- Eduardo Orias
- Department of Molecular, Cellular and Developmental Biology, University of California at Santa Barbara, Santa Barbara, CA 93106, USA.
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38
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Abstract
Histones wrap DNA to form nucleosome particles that compact eukaryotic genomes. Variant histones have evolved crucial roles in chromosome segregation, transcriptional regulation, DNA repair, sperm packaging and other processes. 'Universal' histone variants emerged early in eukaryotic evolution and were later displaced for bulk packaging roles by the canonical histones (H2A, H2B, H3 and H4), the synthesis of which is coupled to DNA replication. Further specializations of histone variants have evolved in some lineages to perform additional tasks. Differences among histone variants in their stability, DNA wrapping, specialized domains that regulate access to DNA, and post-translational modifications, underlie the diverse functions that histones have acquired in evolution.
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39
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Abstract
Centromeres are chromosomal elements that are both necessary and sufficient for chromosome segregation. However, the puzzlingly broad range in centromere complexity, from simple "point" centromeres to multi-megabase arrays of DNA satellites, has defied explanation. We posit that ancestral centromeres were epigenetically defined and that point centromeres, such as those of budding yeast, have derived from the partitioning elements of selfish plasmids. We further propose that the larger centromere sizes in plants and animals and the rapid evolution of their centromeric proteins is the result of an intense battle for evolutionary dominance due to the asymmetric retention of only one product of female meiosis.
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Affiliation(s)
- Harmit S Malik
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA.
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40
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Loidl J, Mochizuki K. Tetrahymena meiotic nuclear reorganization is induced by a checkpoint kinase-dependent response to DNA damage. Mol Biol Cell 2009; 20:2428-37. [PMID: 19297526 PMCID: PMC2675622 DOI: 10.1091/mbc.e08-10-1058] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2008] [Revised: 01/27/2009] [Accepted: 03/05/2009] [Indexed: 11/11/2022] Open
Abstract
In the ciliate Tetrahymena, meiotic micronuclei (MICs) undergo extreme elongation, and meiotic pairing and recombination take place within these elongated nuclei (the "crescents"). We have previously shown that elongation does not occur in the absence of Spo11p-induced DNA double-strand breaks (DSBs). Here we show that elongation is restored in spo11Delta mutants by various DNA-damaging agents including ones that may not cause DSBs to a notable extent. MIC elongation following Spo11p-induced DSBs or artificially induced DNA lesions is probably a DNA-damage response mediated by a phosphokinase signal transduction pathway, since it is suppressed by the ATM/ATR kinase inhibitors caffeine and wortmannin and by knocking out Tetrahymena's ATR orthologue. MIC elongation occurs concomitantly with the movement of centromeres away from the telomeric pole of the MIC. This DNA damage-dependent reorganization of the MIC helps to arrange homologous chromosomes alongside each other but is not sufficient for exact pairing. Thus, Spo11p contributes to bivalent formation in two ways: by creating a favorable spatial disposition of homologues and by stabilizing pairing by crossovers. The polarized chromosome orientation inside the crescent resembles the conserved meiotic bouquet, and crescent and bouquet also share the putative function of aiding meiotic pairing. However, they are regulated differently because in Tetrahymena, DSBs are required for entering rather than exiting this stage.
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Affiliation(s)
- Josef Loidl
- Department of Chromosome Biology and Max F. Perutz Laboratories, Center for Molecular Biology, University of Vienna, A-1030 Vienna, Austria.
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41
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The centromere-drive hypothesis: a simple basis for centromere complexity. PROGRESS IN MOLECULAR AND SUBCELLULAR BIOLOGY 2009; 48:33-52. [PMID: 19521811 DOI: 10.1007/978-3-642-00182-6_2] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Centromeres are far more complex and evolutionarily labile than expected based on their conserved, essential function. The rapid evolution of both centromeric DNA and proteins strongly argue that centromeres are locked in an evolutionary conflict to increase their odds of transmission during asymmetric (female) meiosis. Evolutionary success for "cheating" centromeres can result in highly deleterious consequences for the species, either in terms of skewed sex ratios or male sterility. Centromeric proteins evolve rapidly to suppress the deleterious effects of "centromere-drive." This chapter summarizes the mounting evidence in favor of the centromere-drive model, and its implications for centromere evolution in taxa with variations in meiosis.
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Chromatin: linking structure and function in the nucleolus. Chromosoma 2008; 118:11-23. [PMID: 18925405 DOI: 10.1007/s00412-008-0184-2] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2008] [Revised: 09/17/2008] [Accepted: 09/18/2008] [Indexed: 01/07/2023]
Abstract
The nucleolus is an informative model structure for studying how chromatin-regulated transcription relates to nuclear organisation. In this review, we describe how chromatin controls nucleolar structure through both the modulation of rDNA activity by convergently-evolved remodelling complexes and by direct effects upon rDNA packaging. This packaging not only regulates transcription but may also be important for suppressing internal recombination between tandem rDNA repeats. The identification of nucleolar histone chaperones and novel chromatin proteins by mass spectrometry suggests that structure-specific chromatin components remain to be characterised and may regulate the nucleolus in novel ways. However, it also suggests that there is considerable overlap between nucleolar and non-nucleolar-chromatin components. We conclude that a fuller understanding of nucleolar chromatin will be essential for understanding how gene organisation is linked with nuclear architecture.
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Mochizuki K, Novatchkova M, Loidl J. DNA double-strand breaks, but not crossovers, are required for the reorganization of meiotic nuclei in Tetrahymena. J Cell Sci 2008; 121:2148-58. [PMID: 18522989 PMCID: PMC3184542 DOI: 10.1242/jcs.031799] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
During meiosis, the micronuclei of the ciliated protist Tetrahymena thermophila elongate dramatically. Within these elongated nuclei, chromosomes are arranged in a bouquet-like fashion and homologous pairing and recombination takes place. We studied meiotic chromosome behavior in Tetrahymena in the absence of two genes, SPO11 and a homolog of HOP2 (HOP2A), which have conserved roles in the formation of meiotic DNA double-strand breaks (DSBs) and their repair, respectively. Single-knockout mutants for each gene display only a moderate reduction in chromosome pairing, but show a complete failure to form chiasmata and exhibit chromosome missegregation. The lack of SPO11 prevents the elongation of meiotic nuclei, but it is restored by the artificial induction of DSBs. In the hop2ADelta mutant, the transient appearance of gamma-H2A.X and Rad51p signals indicates the formation and efficient repair of DSBs; but this repair does not occur by interhomolog crossing over. In the absence of HOP2A, the nuclei are elongated, meaning that DSBs but not their conversion to crossovers are required for the development of this meiosis-specific morphology. In addition, by in silico homology searches, we compiled a list of likely Tetrahymena meiotic proteins as the basis for further studies of the unusual synaptonemal complex-less meiosis in this phylogenetically remote model organism.
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Affiliation(s)
- Kazufumi Mochizuki
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), A-1030 Vienna, Austria
| | - Maria Novatchkova
- Research Institute of Molecular Pathology (IMP), A-1030 Vienna, Austria
| | - Josef Loidl
- Department of Chromosome Biology, Max F. Perutz Laboratories, University of Vienna, Dr Bohr Gasse 1, A-1030 Vienna, Austria
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Eisen JA, Coyne RS, Wu M, Wu D, Thiagarajan M, Wortman JR, Badger JH, Ren Q, Amedeo P, Jones KM, Tallon LJ, Delcher AL, Salzberg SL, Silva JC, Haas BJ, Majoros WH, Farzad M, Carlton JM, Smith RK, Garg J, Pearlman RE, Karrer KM, Sun L, Manning G, Elde NC, Turkewitz AP, Asai DJ, Wilkes DE, Wang Y, Cai H, Collins K, Stewart BA, Lee SR, Wilamowska K, Weinberg Z, Ruzzo WL, Wloga D, Gaertig J, Frankel J, Tsao CC, Gorovsky MA, Keeling PJ, Waller RF, Patron NJ, Cherry JM, Stover NA, Krieger CJ, del Toro C, Ryder HF, Williamson SC, Barbeau RA, Hamilton EP, Orias E. Macronuclear genome sequence of the ciliate Tetrahymena thermophila, a model eukaryote. PLoS Biol 2007; 4:e286. [PMID: 16933976 PMCID: PMC1557398 DOI: 10.1371/journal.pbio.0040286] [Citation(s) in RCA: 545] [Impact Index Per Article: 32.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2006] [Accepted: 06/23/2006] [Indexed: 01/05/2023] Open
Abstract
The ciliate Tetrahymena thermophila is a model organism for molecular and cellular biology. Like other ciliates, this species has separate germline and soma functions that are embodied by distinct nuclei within a single cell. The germline-like micronucleus (MIC) has its genome held in reserve for sexual reproduction. The soma-like macronucleus (MAC), which possesses a genome processed from that of the MIC, is the center of gene expression and does not directly contribute DNA to sexual progeny. We report here the shotgun sequencing, assembly, and analysis of the MAC genome of T. thermophila, which is approximately 104 Mb in length and composed of approximately 225 chromosomes. Overall, the gene set is robust, with more than 27,000 predicted protein-coding genes, 15,000 of which have strong matches to genes in other organisms. The functional diversity encoded by these genes is substantial and reflects the complexity of processes required for a free-living, predatory, single-celled organism. This is highlighted by the abundance of lineage-specific duplications of genes with predicted roles in sensing and responding to environmental conditions (e.g., kinases), using diverse resources (e.g., proteases and transporters), and generating structural complexity (e.g., kinesins and dyneins). In contrast to the other lineages of alveolates (apicomplexans and dinoflagellates), no compelling evidence could be found for plastid-derived genes in the genome. UGA, the only T. thermophila stop codon, is used in some genes to encode selenocysteine, thus making this organism the first known with the potential to translate all 64 codons in nuclear genes into amino acids. We present genomic evidence supporting the hypothesis that the excision of DNA from the MIC to generate the MAC specifically targets foreign DNA as a form of genome self-defense. The combination of the genome sequence, the functional diversity encoded therein, and the presence of some pathways missing from other model organisms makes T. thermophila an ideal model for functional genomic studies to address biological, biomedical, and biotechnological questions of fundamental importance.
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Affiliation(s)
- Jonathan A Eisen
- The Institute for Genomic Research, Rockville, Maryland, United States of America.
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Juranek SA, Lipps HJ. New Insights into the Macronuclear Development in Ciliates. INTERNATIONAL REVIEW OF CYTOLOGY 2007; 262:219-51. [PMID: 17631190 DOI: 10.1016/s0074-7696(07)62005-1] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
During macronuclear differentiation in ciliated protozoa, most amazing "DNA gymnastics" takes place, which includes DNA excision, DNA elimination, DNA reorganization, and DNA-specific amplification. Although the morphological events occurring during macronuclear development are well described, a detailed knowledge of the molecular mechanisms and the regulation of this differentiation process is still missing. However, recently several models have been proposed for the molecular regulation of macronuclear differentiation, but these models have yet to be verified experimentally. The scope of this review is to summarize recent discoveries in different ciliate species and to compare and discuss the different models proposed. Results obtained in these studies are not only relevant for our understanding of nuclear differentiation in ciliates, but also for cellular differentiation in eukaryotic organisms in general as well as for other disciplines such as bioinformatics and computational biology.
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Affiliation(s)
- Stefan A Juranek
- Howard Hughes Medical Institute, Laboratory of RNA Molecular Biology, Rockefeller University, New York, New York 10021, USA
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Dawe RK, Henikoff S. Centromeres put epigenetics in the driver's seat. Trends Biochem Sci 2006; 31:662-9. [PMID: 17074489 DOI: 10.1016/j.tibs.2006.10.004] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2006] [Revised: 09/19/2006] [Accepted: 10/20/2006] [Indexed: 01/01/2023]
Abstract
A defining feature of chromosomes is the centromere, the site for spindle attachment at mitosis and meiosis. Intriguingly, centromeres of plants and animals are maintained by both sequence-specific and sequence-independent (epigenetic) processes. Epigenetic inheritance might enable kinetochores (the structures that attach centromeres to spindles) to maintain an optimal size. However, centromeres are susceptible to the evolution of "selfish" DNA repeats that bind to kinetochore proteins. We argue that such sequence-specific interactions are evolutionarily unstable because they enable repeat arrays to influence kinetochore size. Changes in kinetochore size could affect the interaction of kinetochores with the spindle and, in principle, skew Mendelian segregation. We propose that key kinetochore proteins have adapted to disrupt such sequence-specific interactions and restore epigenetic inheritance.
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Affiliation(s)
- R Kelly Dawe
- Department of Plant Biology, University of Georgia, Athens, GA 30602, USA.
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Howard-Till RA, Yao MC. Induction of gene silencing by hairpin RNA expression in Tetrahymena thermophila reveals a second small RNA pathway. Mol Cell Biol 2006; 26:8731-42. [PMID: 17000759 PMCID: PMC1636817 DOI: 10.1128/mcb.01430-06] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Unlike in other eukaryotes, in which it causes gene silencing, RNA interference (RNAi) has been linked to programmed DNA deletion in the ciliate Tetrahymena thermophila. Here we have developed an efficient method to inducibly express double-stranded RNA hairpins and demonstrated that they cause gene silencing through targeted mRNA degradation in all phases of the life cycle, including growth, starvation, and mating. This technique offers a new tool for gene silencing in this model organism. Induction of RNA hairpins causes dramatic upregulation of Dicer and Argonaute family genes, revealing a system capable of rapidly responding to double-stranded RNA. These hairpins are processed into 23- to 24-nucleotide (nt) small RNAs, which are distinctly different from the 28- to 30-nt small RNAs known to be associated with DNA deletion. Thus, two different small RNA pathways appear to be responsible for gene silencing and DNA deletion. Surprisingly, expression of the RNA hairpin also causes targeted DNA deletion during conjugation, although at low efficiencies, which suggests a possible crossover of these two molecular paths.
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Affiliation(s)
- Rachel A Howard-Till
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, 1100 Fairview Ave N., Seattle, WA 98109, USA
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Malik HS, Bayes JJ. Genetic conflicts during meiosis and the evolutionary origins of centromere complexity. Biochem Soc Trans 2006; 34:569-73. [PMID: 16856863 DOI: 10.1042/bst0340569] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Centromeric DNA evolves rapidly, ranging in size and complexity over several orders of magnitude. Traditional attempts at studying centromeres have left unexplained the causes underlying this complexity and rapid evolution. Instead of directly studying centromeric DNA sequence, our approach has been to study the proteins that epigenetically determine centromere identity. We have discovered that centromeric histones (CenH3s) have evolved under positive selection in multiple lineages, suggesting an involvement in recurrent genetic conflict. Our hypothesis is that 'centromere-drive' is the source of this conflict. Under this model, centromeres compete via microtubule attachments for preferential transmission in female meioses occurring in animals and plants. Since only one of four meiotic products will become the egg, this competition confers a selfish advantage to chromosomes that can make more microtubule attachments, resulting in runaway expansions of centromeric satellites. While beneficial to the 'driving' chromosome, these expansions can have deleterious effects on the fitness of an organism and of the species. CenH3s as well as other heterochromatin proteins have evolved under positive selection to suppress the deleterious consequences of 'centromere-drive' by restoring meiotic parity.
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Affiliation(s)
- H S Malik
- Basic Sciences Division, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue N, A1-162, Seattle, WA 98109, USA.
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Cui B, Liu Y, Gorovsky MA. Deposition and function of histone H3 variants in Tetrahymena thermophila. Mol Cell Biol 2006; 26:7719-30. [PMID: 16908532 PMCID: PMC1636873 DOI: 10.1128/mcb.01139-06] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
In Tetrahymena, HHT1 and HHT2 genes encode the same major histone H3; HHT3 and HHT4 encode similar minor H3 variants (H3s), H3.3 and H3.4. Green fluorescent protein (GFP)-tagged H3 is deposited onto chromatin through a DNA replication-coupled (RC) pathway. GFP-tagged H3.3 and H3.4 can be deposited both by a transcription-associated, replication-independent (RI) pathway and also weakly by an RC pathway. Although both types of H3s can be deposited by the RC pathway, DNA repair synthesis associated with meiotic recombination utilizes H3 specifically. The regions distinguishing H3 and H3.3 for their deposition pathways were identified. RC major H3 is not essential. Cells can grow without major H3 if the minor H3s are expressed at high levels. Surprisingly, cells lacking RI H3s are also viable and maintain normal nucleosome density at a highly transcribed region. The RC H3 is not detectably deposited by the RI pathway, even when there are no RI H3s available, indicating that transcription-associated RI H3 deposition is not essential for transcription. Minor H3s are also required to produce viable sexual progeny and play an unexpected role in the germ line micronuclei late in conjugation that is unrelated to transcription.
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Affiliation(s)
- Bowen Cui
- Department of Biology, University of Rochester, Rochester, NY 14627, USA
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Cui B, Gorovsky MA. Centromeric histone H3 is essential for vegetative cell division and for DNA elimination during conjugation in Tetrahymena thermophila. Mol Cell Biol 2006; 26:4499-510. [PMID: 16738316 PMCID: PMC1489134 DOI: 10.1128/mcb.00079-06] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
The Tetrahymena thermophila CNA1 gene encodes the centromeric H3, Cna1p. Green fluorescent protein (GFP)-tagged Cna1p localizes in micronuclei in dots whose number and behavior during mitosis and conjugation are consistent with centromeres. During interphase, Cna1p-GFP localizes in peripheral dots, suggesting centromeres are associated with the nuclear envelope. Newly synthesized Cna1p-GFP enters micronuclei in mitosis and accumulates in the nucleoplasm. Its deposition at centromeres starts at early S phase and continues through most of S phase. CNA1 is required for vegetative cell growth. Knockdown of CNA1 genes in the somatic macronucleus results in micronuclear DNA loss and delayed chromosome segregation during mitosis. During conjugation, Cna1p-GFP disappears from the centromeres in the developing macronucleus, consistent with centromeric sequences being internal eliminated sequences. Surprisingly, zygotic CNA1 is required for efficient elimination of germ line-specific sequences during development of the new macronuclei but not for the RNA interference pathway, through which sequences are targeted for elimination. Zygotically expressed Cna1p localizes in the spherical structures in which the later stages of DNA elimination occur, and these structures cannot be formed in the absence of zygotic CNA1, suggesting that, in addition to functioning in centromeres, Cna1p may also play a role in organizing the formation of the DNA elimination structures.
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Affiliation(s)
- Bowen Cui
- Department of Biology, University of Rochester, Rochester, NY 14627, USA
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