1
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Hu C, Zhu XT, He MH, Shao Y, Qin Z, Wu ZJ, Zhou JQ. Elimination of subtelomeric repeat sequences exerts little effect on telomere essential functions in Saccharomyces cerevisiae. eLife 2024; 12:RP91223. [PMID: 38656297 DOI: 10.7554/elife.91223] [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] [Indexed: 04/26/2024] Open
Abstract
Telomeres, which are chromosomal end structures, play a crucial role in maintaining genome stability and integrity in eukaryotes. In the baker's yeast Saccharomyces cerevisiae, the X- and Y'-elements are subtelomeric repetitive sequences found in all 32 and 17 telomeres, respectively. While the Y'-elements serve as a backup for telomere functions in cells lacking telomerase, the function of the X-elements remains unclear. This study utilized the S. cerevisiae strain SY12, which has three chromosomes and six telomeres, to investigate the role of X-elements (as well as Y'-elements) in telomere maintenance. Deletion of Y'-elements (SY12YΔ), X-elements (SY12XYΔ+Y), or both X- and Y'-elements (SY12XYΔ) did not impact the length of the terminal TG1-3 tracks or telomere silencing. However, inactivation of telomerase in SY12YΔ, SY12XYΔ+Y, and SY12XYΔ cells resulted in cellular senescence and the generation of survivors. These survivors either maintained their telomeres through homologous recombination-dependent TG1-3 track elongation or underwent microhomology-mediated intra-chromosomal end-to-end joining. Our findings indicate the non-essential role of subtelomeric X- and Y'-elements in telomere regulation in both telomerase-proficient and telomerase-null cells and suggest that these elements may represent remnants of S. cerevisiae genome evolution. Furthermore, strains with fewer or no subtelomeric elements exhibit more concise telomere structures and offer potential models for future studies in telomere biology.
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Affiliation(s)
- Can Hu
- The State Key Laboratory of Molecular Biology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences; University of Chinese Academy of Sciences, Shanghai, China
| | - Xue-Ting Zhu
- The State Key Laboratory of Molecular Biology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences; University of Chinese Academy of Sciences, Shanghai, China
| | - Ming-Hong He
- The State Key Laboratory of Molecular Biology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences; University of Chinese Academy of Sciences, Shanghai, China
| | - Yangyang Shao
- Key Laboratory of Synthetic Biology, CAS Center for Excellence in Molecular Plant Sciences, Shanghai Institute of Plant Physiology and Ecology, Chinese Academy of Sciences; University of Chinese Academy of Sciences, Shanghai, China
| | - Zhongjun Qin
- Key Laboratory of Synthetic Biology, CAS Center for Excellence in Molecular Plant Sciences, Shanghai Institute of Plant Physiology and Ecology, Chinese Academy of Sciences; University of Chinese Academy of Sciences, Shanghai, China
| | - Zhi-Jing Wu
- The State Key Laboratory of Molecular Biology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences; University of Chinese Academy of Sciences, Shanghai, China
- Key Laboratory of Systems Health Science of Zhejiang Province, Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences, Hangzhou, China
| | - Jin-Qiu Zhou
- The State Key Laboratory of Molecular Biology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences; University of Chinese Academy of Sciences, Shanghai, China
- Key Laboratory of Systems Health Science of Zhejiang Province, Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences, Hangzhou, China
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2
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Musmaker K, Wells J, Tsai MC, Comeron JM, Malkova A. Alternative Lengthening of Telomeres in Yeast: Old Questions and New Approaches. Biomolecules 2024; 14:113. [PMID: 38254712 PMCID: PMC10813009 DOI: 10.3390/biom14010113] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2023] [Revised: 01/11/2024] [Accepted: 01/12/2024] [Indexed: 01/24/2024] Open
Abstract
Alternative lengthening of telomeres (ALT) is a homologous recombination-based pathway utilized by 10-15% of cancer cells that allows cells to maintain their telomeres in the absence of telomerase. This pathway was originally discovered in the yeast Saccharomyces cerevisiae and, for decades, yeast has served as a robust model to study ALT. Using yeast as a model, two types of ALT (RAD51-dependent and RAD51-independent) have been described. Studies in yeast have provided the phenotypic characterization of ALT survivors, descriptions of the proteins involved, and implicated break-induced replication (BIR) as the mechanism responsible for ALT. Nevertheless, many questions have remained, and answering them has required the development of new quantitative methods. In this review we discuss the historic aspects of the ALT investigation in yeast as well as new approaches to investigating ALT, including ultra-long sequencing, computational modeling, and the use of population genetics. We discuss how employing new methods contributes to our current understanding of the ALT mechanism and how they may expand our understanding of ALT in the future.
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Affiliation(s)
- Kendra Musmaker
- Department of Biology, University of Iowa, Iowa City, IA 52242, USA (J.W.)
| | - Jacob Wells
- Department of Biology, University of Iowa, Iowa City, IA 52242, USA (J.W.)
| | - Meng-Chia Tsai
- Department of Biology, University of Iowa, Iowa City, IA 52242, USA (J.W.)
| | - Josep M. Comeron
- Department of Biology, University of Iowa, Iowa City, IA 52242, USA (J.W.)
- Interdisciplinary Graduate Program in Genetics, University of Iowa, Iowa City, IA 52242, USA
| | - Anna Malkova
- Department of Biology, University of Iowa, Iowa City, IA 52242, USA (J.W.)
- Interdisciplinary Graduate Program in Genetics, University of Iowa, Iowa City, IA 52242, USA
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3
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Aguilera P, Dubarry M, Géli V, Simon MN. NPCs and APBs: two HUBs of non-canonical homology-based recombination at telomeres? Cell Cycle 2023; 22:1163-1168. [PMID: 37128641 PMCID: PMC10193864 DOI: 10.1080/15384101.2023.2206350] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2022] [Revised: 10/05/2022] [Accepted: 10/10/2022] [Indexed: 05/03/2023] Open
Abstract
Apart from a few rare exceptions, the maintenance of functional telomeres by recombination-based mechanisms is restricted to accidental and/or pathological situations. Originally described in the yeast S. cerevisiae, this mode of telomere repair has gained interest with the discovery of telomerase negative cancers that use alternative lengthening of telomeres (ALT cancer) dependent on homologous recombination. In both yeast and humans, it has been shown that recombination at telomeres is spatially regulated and occurs preferentially at the nuclear pore complexes (NPCs) in yeast and at ALT-associated promyelocytic leukemia nuclear bodies (APBs) in human cells. Here, we discuss the potential relationships between these two membrane-less structures and their role in enabling unconventional recombination pathways.
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Affiliation(s)
- Paula Aguilera
- Centro Andaluz de Biologia Molecular y Medicina Regenerativa (CABIMER), Consejo Superior de Investigaciones Cientificas (CSIC), Universidad de Sevilla, Universidad Pablo de Olavide, Seville, Spain
| | - Marion Dubarry
- MAP Laboratory, INSA Lyon, Claude Bernard University UMR5240, Villeurbanne, France
| | - Vincent Géli
- Marseille Cancer Research Center (CRCM), U1068 Inserm, UMR7258 CNRS, Institut Paoli-Calmettes, Equipe labellisee Ligue, Aix Marseille University, Marseille, France
| | - Marie-Noëlle Simon
- Marseille Cancer Research Center (CRCM), U1068 Inserm, UMR7258 CNRS, Institut Paoli-Calmettes, Equipe labellisee Ligue, Aix Marseille University, Marseille, France
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4
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Xiong Y, Zhang H, Zhou S, Ma L, Xiao W, Wu Y, Yuan YJ. Structural Variations and Adaptations of Synthetic Chromosome Ends Driven by SCRaMbLE in Haploid and Diploid Yeasts. ACS Synth Biol 2023; 12:689-699. [PMID: 36821394 DOI: 10.1021/acssynbio.2c00424] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/24/2023]
Abstract
Variations and adaptations of chromosome ends play an important role in eukaryotic karyotype evolution. Traditional experimental studies of the adaptations of chromosome ends mainly rely on the strategy of introducing defects; thus, the adaptation methods of survivors may vary depending on the initial defects. Here, using the SCRaMbLE strategy, we obtained a library of haploid and diploid synthetic strains with variations in chromosome ends. Analysis of the SCRaMbLEd survivors revealed four routes of adaptation: homologous recombination between nonhomologous chromosome arms (haploids) or homologous chromosome arms (diploids), site-specific recombination between intra- or interchromosomal ends, circularization of chromosomes, and loss of whole chromosomes (diploids). We also found that circularization of synthetic chromosomes can be generated by SCRaMbLE. Our study of various adaptation routes of chromosome ends provides insight into eukaryotic karyotype evolution from the viewpoint of synthetic genomics.
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Affiliation(s)
- Yao Xiong
- Frontiers Science Center for Synthetic Biology (Ministry of Education), Tianjin University, Tianjin 300072, China.,Key Laboratory of Systems Bioengineering (Ministry of Education), School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China
| | - Hui Zhang
- Frontiers Science Center for Synthetic Biology (Ministry of Education), Tianjin University, Tianjin 300072, China.,Key Laboratory of Systems Bioengineering (Ministry of Education), School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China
| | - Sijie Zhou
- Frontiers Science Center for Synthetic Biology (Ministry of Education), Tianjin University, Tianjin 300072, China.,Key Laboratory of Systems Bioengineering (Ministry of Education), School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China
| | - Lu Ma
- Frontiers Science Center for Synthetic Biology (Ministry of Education), Tianjin University, Tianjin 300072, China.,Key Laboratory of Systems Bioengineering (Ministry of Education), School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China
| | - Wenhai Xiao
- Frontiers Science Center for Synthetic Biology (Ministry of Education), Tianjin University, Tianjin 300072, China.,Key Laboratory of Systems Bioengineering (Ministry of Education), School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China
| | - Yi Wu
- Frontiers Science Center for Synthetic Biology (Ministry of Education), Tianjin University, Tianjin 300072, China.,Key Laboratory of Systems Bioengineering (Ministry of Education), School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China
| | - Ying-Jin Yuan
- Frontiers Science Center for Synthetic Biology (Ministry of Education), Tianjin University, Tianjin 300072, China.,Key Laboratory of Systems Bioengineering (Ministry of Education), School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China
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5
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Casari E, Gnugnoli M, Rinaldi C, Pizzul P, Colombo CV, Bonetti D, Longhese MP. To Fix or Not to Fix: Maintenance of Chromosome Ends Versus Repair of DNA Double-Strand Breaks. Cells 2022; 11:cells11203224. [PMID: 36291091 PMCID: PMC9601279 DOI: 10.3390/cells11203224] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2022] [Revised: 10/07/2022] [Accepted: 10/12/2022] [Indexed: 02/08/2023] Open
Abstract
Early work by Muller and McClintock discovered that the physical ends of linear chromosomes, named telomeres, possess an inherent ability to escape unwarranted fusions. Since then, extensive research has shown that this special feature relies on specialized proteins and structural properties that confer identity to the chromosome ends, thus allowing cells to distinguish them from intrachromosomal DNA double-strand breaks. Due to the inability of conventional DNA replication to fully replicate the chromosome ends and the downregulation of telomerase in most somatic human tissues, telomeres shorten as cells divide and lose this protective capacity. Telomere attrition causes the activation of the DNA damage checkpoint that leads to a cell-cycle arrest and the entering of cells into a nondividing state, called replicative senescence, that acts as a barrier against tumorigenesis. However, downregulation of the checkpoint overcomes this barrier and leads to further genomic instability that, if coupled with re-stabilization of telomeres, can drive tumorigenesis. This review focuses on the key experiments that have been performed in the model organism Saccharomyces cerevisiae to uncover the mechanisms that protect the chromosome ends from eliciting a DNA damage response, the conservation of these pathways in mammals, as well as the consequences of their loss in human cancer.
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6
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Aguilera P, Dubarry M, Hardy J, Lisby M, Simon MN, Géli V. Telomeric C-circles localize at nuclear pore complexes in Saccharomyces cerevisiae. EMBO J 2022; 41:e108736. [PMID: 35147992 PMCID: PMC8922269 DOI: 10.15252/embj.2021108736] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2021] [Revised: 01/17/2022] [Accepted: 01/21/2022] [Indexed: 11/09/2022] Open
Abstract
As in human cells, yeast telomeres can be maintained in cells lacking telomerase activity by recombination-based mechanisms known as ALT (Alternative Lengthening of Telomeres). A hallmark of ALT human cancer cells are extrachromosomal telomeric DNA elements called C-circles, whose origin and function have remained unclear. Here, we show that extrachromosomal telomeric C-circles in yeast can be detected shortly after senescence crisis and concomitantly with the production of survivors arising from "type II" recombination events. We uncover that C-circles bind to the nuclear pore complex (NPC) and to the SAGA-TREX2 complex, similar to other non-centromeric episomal DNA. Disrupting the integrity of the SAGA/TREX2 complex affects both C-circle binding to NPCs and type II telomere recombination, suggesting that NPC tethering of C-circles facilitates formation and/or propagation of the long telomere repeats characteristic of type II survivors. Furthermore, we find that disruption of the nuclear diffusion barrier impairs type II recombination. These results support a model in which concentration of C-circles at NPCs benefits type II telomere recombination, highlighting the importance of spatial coordination in ALT-type mechanisms of telomere maintenance.
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Affiliation(s)
- Paula Aguilera
- Marseille Cancer Research Center (CRCM), U1068 Inserm, UMR7258 CNRS, Institut Paoli-Calmettes, Equipe labellisée Ligue, Aix Marseille University, Marseille, France
| | - Marion Dubarry
- Marseille Cancer Research Center (CRCM), U1068 Inserm, UMR7258 CNRS, Institut Paoli-Calmettes, Equipe labellisée Ligue, Aix Marseille University, Marseille, France
| | - Julien Hardy
- Marseille Cancer Research Center (CRCM), U1068 Inserm, UMR7258 CNRS, Institut Paoli-Calmettes, Equipe labellisée Ligue, Aix Marseille University, Marseille, France
| | - Michael Lisby
- Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Marie-Noëlle Simon
- Marseille Cancer Research Center (CRCM), U1068 Inserm, UMR7258 CNRS, Institut Paoli-Calmettes, Equipe labellisée Ligue, Aix Marseille University, Marseille, France
| | - Vincent Géli
- Marseille Cancer Research Center (CRCM), U1068 Inserm, UMR7258 CNRS, Institut Paoli-Calmettes, Equipe labellisée Ligue, Aix Marseille University, Marseille, France
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7
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Kockler ZW, Osia B, Lee R, Musmaker K, Malkova A. Repair of DNA Breaks by Break-Induced Replication. Annu Rev Biochem 2021; 90:165-191. [PMID: 33792375 DOI: 10.1146/annurev-biochem-081420-095551] [Citation(s) in RCA: 38] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Double-strand DNA breaks (DSBs) are the most lethal type of DNA damage, making DSB repair critical for cell survival. However, some DSB repair pathways are mutagenic and promote genome rearrangements, leading to genome destabilization. One such pathway is break-induced replication (BIR), which repairs primarily one-ended DSBs, similar to those formed by collapsed replication forks or telomere erosion. BIR is initiated by the invasion of a broken DNA end into a homologous template, synthesizes new DNA within the context of a migrating bubble, and is associated with conservative inheritance of new genetic material. This mode of synthesis is responsible for a high level of genetic instability associated with BIR. Eukaryotic BIR was initially investigated in yeast, but now it is also actively studied in mammalian systems. Additionally, a significant breakthrough has been made regarding the role of microhomology-mediated BIR in the formation of complex genomic rearrangements that underly various human pathologies.
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Affiliation(s)
- Z W Kockler
- Department of Biology, University of Iowa, Iowa City, Iowa 52242, USA;
| | - B Osia
- Department of Biology, University of Iowa, Iowa City, Iowa 52242, USA;
| | - R Lee
- Department of Biology, University of Iowa, Iowa City, Iowa 52242, USA;
| | - K Musmaker
- Department of Biology, University of Iowa, Iowa City, Iowa 52242, USA;
| | - A Malkova
- Department of Biology, University of Iowa, Iowa City, Iowa 52242, USA;
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8
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Kockler ZW, Comeron JM, Malkova A. A unified alternative telomere-lengthening pathway in yeast survivor cells. Mol Cell 2021; 81:1816-1829.e5. [PMID: 33639094 DOI: 10.1016/j.molcel.2021.02.004] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2020] [Revised: 06/28/2020] [Accepted: 02/01/2021] [Indexed: 10/24/2022]
Abstract
Alternative lengthening of telomeres (ALT) is a recombination process that maintains telomeres in the absence of telomerase and helps cancer cells to survive. Yeast has been used as a robust model of ALT; however, the inability to determine the frequency and structure of ALT survivors hinders understanding of the ALT mechanism. Here, using population and molecular genetics approaches, we overcome these problems and demonstrate that contrary to the current view, both RAD51-dependent and RAD51-independent mechanisms are required for a unified ALT survivor pathway. This conclusion is based on the calculation of ALT frequencies, as well as on ultra-long sequencing of ALT products that revealed hybrid sequences containing features attributed to both recombination pathways. Sequencing of ALT intermediates demonstrates that recombination begins with Rad51-mediated strand invasion to form DNA substrates that are matured by a Rad51-independent ssDNA annealing pathway. A similar unified ALT pathway may operate in other organisms, including humans.
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Affiliation(s)
- Zachary W Kockler
- Department of Biology, University of Iowa, Iowa City, IA 52245, USA; Interdisciplinary Graduate Program in Genetics, University of Iowa, Iowa City, IA 52245, USA
| | - Josep M Comeron
- Department of Biology, University of Iowa, Iowa City, IA 52245, USA; Interdisciplinary Graduate Program in Genetics, University of Iowa, Iowa City, IA 52245, USA.
| | - Anna Malkova
- Department of Biology, University of Iowa, Iowa City, IA 52245, USA; Interdisciplinary Graduate Program in Genetics, University of Iowa, Iowa City, IA 52245, USA.
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9
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Grandin N, Gallego ME, White CI, Charbonneau M. Inhibition of the alternative lengthening of telomeres pathway by subtelomeric sequences in Saccharomyces cerevisiae. DNA Repair (Amst) 2020; 96:102996. [PMID: 33126043 DOI: 10.1016/j.dnarep.2020.102996] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2020] [Revised: 09/24/2020] [Accepted: 10/04/2020] [Indexed: 10/23/2022]
Abstract
In the budding yeast Saccharomyces cerevisiae, telomerase is constitutively active and is essential for chromosome end protection and illimited proliferation of cell populations. However, upon inactivation of telomerase, alternative mechanims of telomere maintenance allow proliferation of only extremely rare survivors. S. cerevisiae type I and type II survivors differ by the nature of the donor sequences used for repair by homologous recombination of the uncapped terminal TG1-3 telomeric sequences. Type I amplifies the subtelomeric Y' sequences and is more efficient than type II, which amplifies the terminal TG1-3 repeats. However, type II survivors grow faster than type I survivors and can easily outgrow them in liquid cultures. The mechanistic interest of studying S. cerevisiae telomeric recombination is reinforced by the fact that type II recombination is the equivalent of the alternative lengthening of telomeres (ALT) pathway that is used by 5-15 % of cancer types as an alternative to telomerase reactivation. In budding yeast, only around half of the 32 telomeres harbor Y' subtelomeric elements. We report here that in strains harboring Y' elements on all telomeres, type II survivors are not observed, most likely due to an increase in the efficiency of type I recombination. However, in a temperature-sensitive cdc13-1 mutant grown at semi-permissive temperature, the increased amount of telomeric TG1-3 repeats could overcome type II inhibition by the subtelomeric Y' sequences. Strikingly, in the 100 % Y' strain the replicative senescence crisis normally provoked by inactivation of telomerase completely disappeared and the severity of the crisis was proportional to the percentage of chromosome-ends lacking Y' subtelomeric sequences. The present study highlights the fact that the nature of subtelomeric elements can influence the selection of the pathway of telomere maintenance by recombination, as well as the response of the cell to telomeric damage caused by telomerase inactivation.
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Affiliation(s)
- Nathalie Grandin
- GReD Institute, CNRS UMR6293, INSERM U1103, Faculty of Medicine, University Clermont-Auvergne, 28 place Henri Dunant, BP 38, 63001 Clermont-Ferrand Cedex, France
| | - Maria Eugenia Gallego
- GReD Institute, CNRS UMR6293, INSERM U1103, Faculty of Medicine, University Clermont-Auvergne, 28 place Henri Dunant, BP 38, 63001 Clermont-Ferrand Cedex, France
| | - Charles I White
- GReD Institute, CNRS UMR6293, INSERM U1103, Faculty of Medicine, University Clermont-Auvergne, 28 place Henri Dunant, BP 38, 63001 Clermont-Ferrand Cedex, France
| | - Michel Charbonneau
- GReD Institute, CNRS UMR6293, INSERM U1103, Faculty of Medicine, University Clermont-Auvergne, 28 place Henri Dunant, BP 38, 63001 Clermont-Ferrand Cedex, France.
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10
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Wu ZJ, Liu JC, Man X, Gu X, Li TY, Cai C, He MH, Shao Y, Lu N, Xue X, Qin Z, Zhou JQ. Cdc13 is predominant over Stn1 and Ten1 in preventing chromosome end fusions. eLife 2020; 9:53144. [PMID: 32755541 PMCID: PMC7406354 DOI: 10.7554/elife.53144] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2019] [Accepted: 06/12/2020] [Indexed: 12/16/2022] Open
Abstract
Telomeres define the natural ends of eukaryotic chromosomes and are crucial for chromosomal stability. The budding yeast Cdc13, Stn1 and Ten1 proteins form a heterotrimeric complex, and the inactivation of any of its subunits leads to a uniformly lethal phenotype due to telomere deprotection. Although Cdc13, Stn1 and Ten1 seem to belong to an epistasis group, it remains unclear whether they function differently in telomere protection. Here, we employed the single-linear-chromosome yeast SY14, and surprisingly found that the deletion of CDC13 leads to telomere erosion and intrachromosome end-to-end fusion, which depends on Rad52 but not Yku. Interestingly, the emergence frequency of survivors in the SY14 cdc13Δ mutant was ~29 fold higher than that in either the stn1Δ or ten1Δ mutant, demonstrating a predominant role of Cdc13 in inhibiting telomere fusion. Chromosomal fusion readily occurred in the telomerase-null SY14 strain, further verifying the default role of intact telomeres in inhibiting chromosome fusion.
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Affiliation(s)
- Zhi-Jing Wu
- The State Key Laboratory of Molecular Biology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences; University of Chinese Academy of Sciences, Shanghai, China
| | - Jia-Cheng Liu
- The State Key Laboratory of Molecular Biology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences; University of Chinese Academy of Sciences, Shanghai, China
| | - Xin Man
- The State Key Laboratory of Molecular Biology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences; University of Chinese Academy of Sciences, Shanghai, China
| | - Xin Gu
- The State Key Laboratory of Molecular Biology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences; University of Chinese Academy of Sciences, Shanghai, China
| | - Ting-Yi Li
- The State Key Laboratory of Molecular Biology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences; University of Chinese Academy of Sciences, Shanghai, China
| | - Chen Cai
- The State Key Laboratory of Molecular Biology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences; University of Chinese Academy of Sciences, Shanghai, China.,School of Life Science and Technology, ShanghaiTech University, Shanghai, China
| | - Ming-Hong He
- The State Key Laboratory of Molecular Biology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences; University of Chinese Academy of Sciences, Shanghai, China
| | - Yangyang Shao
- Key Laboratory of Synthetic Biology, CAS Center for Excellence in Molecular Plant Sciences, Shanghai Institute of Plant Physiology and Ecology, Chinese Academy of Sciences; University of Chinese Academy of Sciences, Shanghai, China
| | - Ning Lu
- Key Laboratory of Synthetic Biology, CAS Center for Excellence in Molecular Plant Sciences, Shanghai Institute of Plant Physiology and Ecology, Chinese Academy of Sciences; University of Chinese Academy of Sciences, Shanghai, China
| | - Xiaoli Xue
- Key Laboratory of Synthetic Biology, CAS Center for Excellence in Molecular Plant Sciences, Shanghai Institute of Plant Physiology and Ecology, Chinese Academy of Sciences; University of Chinese Academy of Sciences, Shanghai, China
| | - Zhongjun Qin
- Key Laboratory of Synthetic Biology, CAS Center for Excellence in Molecular Plant Sciences, Shanghai Institute of Plant Physiology and Ecology, Chinese Academy of Sciences; University of Chinese Academy of Sciences, Shanghai, China
| | - Jin-Qiu Zhou
- The State Key Laboratory of Molecular Biology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences; University of Chinese Academy of Sciences, Shanghai, China.,School of Life Science and Technology, ShanghaiTech University, Shanghai, China
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11
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Tomáška Ľ, Cesare AJ, AlTurki TM, Griffith JD. Twenty years of t-loops: A case study for the importance of collaboration in molecular biology. DNA Repair (Amst) 2020; 94:102901. [PMID: 32620538 DOI: 10.1016/j.dnarep.2020.102901] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2020] [Accepted: 06/22/2020] [Indexed: 12/12/2022]
Abstract
Collaborative studies open doors to breakthroughs otherwise unattainable by any one laboratory alone. Here we describe the initial collaboration between the Griffith and de Lange laboratories that led to thinking about the telomere as a DNA template for homologous recombination, the proposal of telomere looping, and the first electron micrographs of t-loops. This was followed by collaborations that revealed t-loops across eukaryotic phyla. The Griffith and Tomáška/Nosek collaboration revealed circular telomeric DNA (t-circles) derived from the linear mitochondrial chromosomes of nonconventional yeast, which spurred discovery of t-circles in ALT-positive human cells. Collaborative work between the Griffith and McEachern labs demonstrated t-loops and t-circles in a series of yeast species. The de Lange and Zhuang laboratories then applied super-resolution light microscopy to demonstrate a genetic role for TRF2 in loop formation. Recent work from the Griffith laboratory linked telomere transcription with t-loop formation, providing a new model of the t-loop junction. A recent collaboration between the Cesare and Gaus laboratories utilized super-resolution light microscopy to provide details about t-loops as protective elements, followed by the Boulton and Cesare laboratories showing how cell cycle regulation of TRF2 and RTEL enables t-loop opening and reformation to promote telomere replication. Twenty years after the discovery of t-loops, we reflect on the collective history of their research as a case study in collaborative molecular biology.
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Affiliation(s)
- Ľubomír Tomáška
- Department of Genetics, Comenius University in Bratislava, Faculty of Natural Sciences, Ilkovicova 6, 84215, Bratislava, Slovakia
| | - Anthony J Cesare
- Genome Integrity Unit, Children's Medical Research Institute, University of Sydney, Westmead, NSW, 2145, Australia
| | - Taghreed M AlTurki
- Lineberger Comprehensive Cancer Center and Departments of Microbiology and Immunology, and Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA
| | - Jack D Griffith
- Lineberger Comprehensive Cancer Center and Departments of Microbiology and Immunology, and Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA.
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12
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Cacchione S, Cenci G, Raffa GD. Silence at the End: How Drosophila Regulates Expression and Transposition of Telomeric Retroelements. J Mol Biol 2020; 432:4305-4321. [PMID: 32512004 DOI: 10.1016/j.jmb.2020.06.004] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2020] [Revised: 05/25/2020] [Accepted: 06/02/2020] [Indexed: 01/26/2023]
Abstract
The maintenance of chromosome ends in Drosophila is an exceptional phenomenon because it relies on the transposition of specialized retrotransposons rather than on the activity of the enzyme telomerase that maintains telomeres in almost every other eukaryotic species. Sequential transpositions of Het-A, TART, and TAHRE (HTT) onto chromosome ends produce long head-to-tail arrays that are reminiscent to the long arrays of short repeats produced by telomerase in other organisms. Coordinating the activation and silencing of the HTT array with the recruitment of telomere capping proteins favors proper telomere function. However, how this coordination is achieved is not well understood. Like other Drosophila retrotransposons, telomeric elements are regulated by the piRNA pathway. Remarkably, HTT arrays are both source of piRNA and targets of gene silencing thus making the regulation of Drosophila telomeric transposons a unique event among eukaryotes. Herein we will review the genetic and molecular mechanisms underlying the regulation of HTT transcription and transposition and will discuss the possibility of a crosstalk between piRNA-mediated regulation, telomeric chromatin establishment, and telomere protection.
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Affiliation(s)
- Stefano Cacchione
- Department of Biology and Biotechnology, Sapienza University of Rome, P.le Aldo Moro 5, 00185 Roma, Italy.
| | - Giovanni Cenci
- Department of Biology and Biotechnology, Sapienza University of Rome, P.le Aldo Moro 5, 00185 Roma, Italy; Fondazione Cenci Bolognetti, Istituto Pasteur, Rome, Italy.
| | - Grazia Daniela Raffa
- Department of Biology and Biotechnology, Sapienza University of Rome, P.le Aldo Moro 5, 00185 Roma, Italy.
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13
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Feng JX, Riddle NC. Epigenetics and genome stability. Mamm Genome 2020; 31:181-195. [PMID: 32296924 DOI: 10.1007/s00335-020-09836-2] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2019] [Accepted: 04/07/2020] [Indexed: 12/19/2022]
Abstract
Maintaining genome stability is essential to an organism's health and survival. Breakdown of the mechanisms protecting the genome and the resulting genome instability are an important aspect of the aging process and have been linked to diseases such as cancer. Thus, a large network of interconnected pathways is responsible for ensuring genome integrity in the face of the continuous challenges that induce DNA damage. While these pathways are diverse, epigenetic mechanisms play a central role in many of them. DNA modifications, histone variants and modifications, chromatin structure, and non-coding RNAs all carry out a variety of functions to ensure that genome stability is maintained. Epigenetic mechanisms ensure the functions of centromeres and telomeres that are essential for genome stability. Epigenetic mechanisms also protect the genome from the invasion by transposable elements and contribute to various DNA repair pathways. In this review, we highlight the integral role of epigenetic mechanisms in the maintenance of genome stability and draw attention to issues in need of further study.
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Affiliation(s)
- Justina X Feng
- Department of Biology, The University of Alabama at Birmingham, Birmingham, AL, USA
| | - Nicole C Riddle
- Department of Biology, The University of Alabama at Birmingham, Birmingham, AL, USA.
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14
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Mersaoui SY, Bonnell E, Wellinger RJ. Nuclear import of Cdc13 limits chromosomal capping. Nucleic Acids Res 2019; 46:2975-2989. [PMID: 29432594 PMCID: PMC5887288 DOI: 10.1093/nar/gky085] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2017] [Accepted: 01/30/2018] [Indexed: 12/15/2022] Open
Abstract
Cdc13 is an essential protein involved in telomere maintenance and chromosome capping. Individual domain analyses on Cdc13 suggest the presence of four distinct OB-fold domains and one recruitment domain. However, it remained unclear how these sub-domains function in the context of the whole protein in vivo. Here, we use individual single domain deletions to address their roles in telomere capping. We find that the OB2 domain contains a nuclear localization signal that is essential for nuclear import of Cdc13 and therefore is required for chromosome capping. The karyopherin Msn5 is important for nuclear localization, and retention of Cdc13 in the nucleus also requires its binding to telomeres. Moreover, Cdc13 homodimerization occurs even if the protein is not bound to DNA and is in the cytoplasm. Hence, Cdc13 abundance in the nucleus and, in consequence, its capping function is strongly affected by nucleo-cytoplasmic transport as well as nuclear retention by DNA binding.
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Affiliation(s)
- Sofiane Y Mersaoui
- Department of Microbiology and Infectiology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, 3201 Rue Jean Mignault, Sherbrooke, QC J1E 4K8, Canada
| | - Erin Bonnell
- Department of Microbiology and Infectiology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, 3201 Rue Jean Mignault, Sherbrooke, QC J1E 4K8, Canada
| | - Raymund J Wellinger
- Department of Microbiology and Infectiology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, 3201 Rue Jean Mignault, Sherbrooke, QC J1E 4K8, Canada
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15
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Olivier M, Charbonnel C, Amiard S, White CI, Gallego ME. RAD51 and RTEL1 compensate telomere loss in the absence of telomerase. Nucleic Acids Res 2019; 46:2432-2445. [PMID: 29346668 PMCID: PMC5861403 DOI: 10.1093/nar/gkx1322] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2017] [Accepted: 01/09/2018] [Indexed: 11/23/2022] Open
Abstract
Replicative erosion of telomeres is naturally compensated by telomerase and studies in yeast and vertebrates show that homologous recombination can compensate for the absence of telomerase. We show that RAD51 protein, which catalyzes the key strand-invasion step of homologous recombination, is localized at Arabidopsis telomeres in absence of telomerase. Blocking the strand-transfer activity of the RAD51 in telomerase mutant plants results in a strikingly earlier onset of developmental defects, accompanied by increased numbers of end-to-end chromosome fusions. Imposing replication stress through knockout of RNaseH2 increases numbers of chromosome fusions and reduces the survival of these plants deficient for telomerase and homologous recombination. This finding suggests that RAD51-dependent homologous recombination acts as an essential backup to the telomerase for compensation of replicative telomere loss to ensure genome stability. Furthermore, we show that this positive role of RAD51 in telomere stability is dependent on the RTEL1 helicase. We propose that a RAD51 dependent break-induced replication process is activated in cells lacking telomerase activity, with RTEL1 responsible for D-loop dissolution after telomere replication.
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Affiliation(s)
- Margaux Olivier
- Génétique, Reproduction et Développement, UMR CNRS 6293 - INSERM U1103 - Université Clermont Auvergne, Faculté de Médecine. 28, place Henri Dunant - BP38 63001 Clermont-Ferrand Cedex 1, France
| | - Cyril Charbonnel
- Génétique, Reproduction et Développement, UMR CNRS 6293 - INSERM U1103 - Université Clermont Auvergne, Faculté de Médecine. 28, place Henri Dunant - BP38 63001 Clermont-Ferrand Cedex 1, France
| | - Simon Amiard
- Génétique, Reproduction et Développement, UMR CNRS 6293 - INSERM U1103 - Université Clermont Auvergne, Faculté de Médecine. 28, place Henri Dunant - BP38 63001 Clermont-Ferrand Cedex 1, France
| | - Charles I White
- Génétique, Reproduction et Développement, UMR CNRS 6293 - INSERM U1103 - Université Clermont Auvergne, Faculté de Médecine. 28, place Henri Dunant - BP38 63001 Clermont-Ferrand Cedex 1, France
| | - Maria E Gallego
- Génétique, Reproduction et Développement, UMR CNRS 6293 - INSERM U1103 - Université Clermont Auvergne, Faculté de Médecine. 28, place Henri Dunant - BP38 63001 Clermont-Ferrand Cedex 1, France
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16
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Upregulation of dNTP Levels After Telomerase Inactivation Influences Telomerase-Independent Telomere Maintenance Pathway Choice in Saccharomyces cerevisiae. G3-GENES GENOMES GENETICS 2018; 8:2551-2558. [PMID: 29848621 PMCID: PMC6071591 DOI: 10.1534/g3.118.200280] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In 10–15% of cancers, telomere length is maintained by a telomerase-independent, recombination-mediated pathway called alternative lengthening of telomeres (ALT). ALT mechanisms were first seen, and have been best studied, in telomerase-null Saccharomyces cerevisiae cells called “survivors”. There are two main types of survivors. Type I survivors amplify Y′ subtelomeric elements while type II survivors, similar to the majority of human ALT cells, amplify the terminal telomeric repeats. Both types of survivors require Rad52, a key homologous recombination protein, and Pol32, a non-essential subunit of DNA polymerase δ. A number of additional proteins have been reported to be important for either type I or type II survivor formation, but it is still unclear how these two pathways maintain telomeres. In this study, we performed a genome-wide screen to identify novel genes that are important for the formation of type II ALT-like survivors. We identified 23 genes that disrupt type II survivor formation when deleted. 17 of these genes had not been previously reported to do so. Several of these genes (DUN1, CCR4, and MOT2) are known to be involved in the regulation of dNTP levels. We find that dNTP levels are elevated early after telomerase inactivation and that this increase favors the formation of type II survivors.
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17
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Kim C, Yang J, Jeong SH, Kim H, Park GH, Shin HB, Ro M, Kim KY, Park Y, Kim KP, Kwack K. Yeast-based assays for characterization of the functional effects of single nucleotide polymorphisms in human DNA repair genes. PLoS One 2018; 13:e0193823. [PMID: 29522548 PMCID: PMC5844570 DOI: 10.1371/journal.pone.0193823] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2017] [Accepted: 02/20/2018] [Indexed: 01/03/2023] Open
Abstract
DNA repair mechanisms maintain genomic integrity upon exposure to various types of DNA damage, which cause either single- or double-strand breaks in the DNA. Here, we propose a strategy for the functional study of single nucleotide polymorphisms (SNPs) in the human DNA repair genes XPD/ERCC2, RAD18, and KU70/XRCC6 and the checkpoint activation gene ATR that are essentially involved in the cell cycle and DNA damage repair. We analyzed the mutational effects of the DNA repair genes under DNA-damaging conditions, including ultraviolet irradiation and treatment with genotoxic reagents, using a Saccharomyces cerevisiae system to overcome the limitations of the human cell-based assay. We identified causal variants from selected SNPs in the present analyses. (i) R594C SNP in RAD3 (human XPD/ERCC2) caused severe reductions in the growth rate of mutant cells upon short-wavelength UV irradiation or chemical reagent treatment. (ii) The growth rates of the selected variants in RAD18, YKU70, and MEC1 were similar to those of wild-type cells on methyl methanesulfonate and hydroxyurea treated media. (iii) We also assessed the structural impact of the SNPs by analyzing differences in the structural conformation and calculating the root mean square deviation, which is a measure of the discordance of the Cα atoms between protein structures. Based on the above results, we propose that these analytical approaches serve as efficient methods for the identification of causal variants of human disease-causing genes and elucidation of yeast-cell based molecular mechanisms.
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Affiliation(s)
- Changshin Kim
- Department of Biomedical Science, College of Life Science, CHA University, Seongnam-si, Gyeonggi-do, Republic of Korea
| | - Jinmo Yang
- Department of Biomedical Science, College of Life Science, CHA University, Seongnam-si, Gyeonggi-do, Republic of Korea
| | - Su-Hyun Jeong
- Department of Biomedical Science, College of Life Science, CHA University, Seongnam-si, Gyeonggi-do, Republic of Korea
| | - Hayoung Kim
- Department of Biomedical Science, College of Life Science, CHA University, Seongnam-si, Gyeonggi-do, Republic of Korea
| | - Geun-hee Park
- Department of Biomedical Science, College of Life Science, CHA University, Seongnam-si, Gyeonggi-do, Republic of Korea
| | - Hwa Beom Shin
- Department of Biomedical Science, College of Life Science, CHA University, Seongnam-si, Gyeonggi-do, Republic of Korea
| | - MyungJa Ro
- Department of Biomedical Science, College of Life Science, CHA University, Seongnam-si, Gyeonggi-do, Republic of Korea
| | - Kyoung-Yeon Kim
- Department of Biomedical Science, College of Life Science, CHA University, Seongnam-si, Gyeonggi-do, Republic of Korea
| | - YoungJoon Park
- Department of Biomedical Science, College of Life Science, CHA University, Seongnam-si, Gyeonggi-do, Republic of Korea
| | - Keun Pil Kim
- Department of Life Sciences, College of Natural Sciences, Chung-Ang University, Seoul, Republic of Korea
| | - KyuBum Kwack
- Department of Biomedical Science, College of Life Science, CHA University, Seongnam-si, Gyeonggi-do, Republic of Korea
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18
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Beletsky AV, Malyavko AN, Sukhanova MV, Mardanova ES, Zvereva MI, Petrova OA, Parfenova YY, Rubtsova MP, Mardanov AV, Lavrik OI, Dontsova OA, Ravin NV. The genome-wide transcription response to telomerase deficiency in the thermotolerant yeast Hansenula polymorpha DL-1. BMC Genomics 2017; 18:492. [PMID: 28659185 PMCID: PMC5490237 DOI: 10.1186/s12864-017-3889-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2017] [Accepted: 06/21/2017] [Indexed: 01/04/2023] Open
Abstract
BACKGROUND In the course of replication of eukaryotic chromosomes, the telomere length is maintained due to activity of telomerase, the ribonucleoprotein reverse transcriptase. Abolishing telomerase function causes progressive shortening of telomeres and, ultimately, cell cycle arrest and replicative senescence. To better understand the cellular response to telomerase deficiency, we performed a transcriptomic study for the thermotolerant methylotrophic yeast Hansenula polymorpha DL-1 lacking telomerase activity. RESULTS Mutant strain of H. polymorpha carrying a disrupted telomerase RNA gene was produced, grown to senescence and analyzed by RNA-seq along with wild type strain. Telomere shortening induced a transcriptional response involving genes relevant to telomere structure and maintenance, DNA damage response, information processing, and some metabolic pathways. Genes involved in DNA replication and repair, response to environmental stresses and intracellular traffic were up-regulated in senescent H. polymorpha cells, while strong down-regulation was observed for genes involved in transcription and translation, as well as core histones. CONCLUSIONS Comparison of the telomerase deletion transcription responses by Saccharomyces cerevisiae and H. polymorpha demonstrates that senescence makes different impact on the main metabolic pathways of these yeast species but induces similar changes in processes related to nucleic acids metabolism and protein synthesis. Up-regulation of a subunit of the TORC1 complex is clearly relevant for both types of yeast.
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Affiliation(s)
- Alexey V Beletsky
- Institute of Bioengineering, Research Center of Biotechnology of the Russian Academy of Sciences, Leninsky Ave. 33, bld 2, Moscow, 119071, Russia
| | - Alexander N Malyavko
- Faculty of Chemistry, Moscow State University, Leninskie Gory 1, bld. 3, Moscow, 119991, Russia.,Center of Functional Genomics, Skolkovo Institute of Science and Technology, Moscow, 143026, Russia
| | - Maria V Sukhanova
- Institute of Chemical Biology and Fundamental Medicine, Siberian Branch, Russian Academy of Sciences, Lavrentiev Ave. 8, Novosibirsk, 630090, Russia
| | - Eugenia S Mardanova
- Institute of Bioengineering, Research Center of Biotechnology of the Russian Academy of Sciences, Leninsky Ave. 33, bld 2, Moscow, 119071, Russia
| | - Maria I Zvereva
- Faculty of Chemistry, Moscow State University, Leninskie Gory 1, bld. 3, Moscow, 119991, Russia
| | - Olga A Petrova
- Belozersky Institute of Physico-Chemical Biology, Moscow State University, Leninskie Gory 1, bld. 40, Moscow, 119992, Russia
| | - Yulia Yu Parfenova
- Faculty of Chemistry, Moscow State University, Leninskie Gory 1, bld. 3, Moscow, 119991, Russia
| | - Maria P Rubtsova
- Faculty of Chemistry, Moscow State University, Leninskie Gory 1, bld. 3, Moscow, 119991, Russia
| | - Andrey V Mardanov
- Institute of Bioengineering, Research Center of Biotechnology of the Russian Academy of Sciences, Leninsky Ave. 33, bld 2, Moscow, 119071, Russia
| | - Olga I Lavrik
- Institute of Chemical Biology and Fundamental Medicine, Siberian Branch, Russian Academy of Sciences, Lavrentiev Ave. 8, Novosibirsk, 630090, Russia.,Novosibirsk State University, Novosibirsk, 630090, Russia
| | - Olga A Dontsova
- Faculty of Chemistry, Moscow State University, Leninskie Gory 1, bld. 3, Moscow, 119991, Russia.,Belozersky Institute of Physico-Chemical Biology, Moscow State University, Leninskie Gory 1, bld. 40, Moscow, 119992, Russia.,Center of Functional Genomics, Skolkovo Institute of Science and Technology, Moscow, 143026, Russia
| | - Nikolai V Ravin
- Institute of Bioengineering, Research Center of Biotechnology of the Russian Academy of Sciences, Leninsky Ave. 33, bld 2, Moscow, 119071, Russia.
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19
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Apte MS, Cooper JP. Life and cancer without telomerase: ALT and other strategies for making sure ends (don't) meet. Crit Rev Biochem Mol Biol 2016; 52:57-73. [PMID: 27892716 DOI: 10.1080/10409238.2016.1260090] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
While most cancer cells rely on telomerase expression/re-activation for linear chromosome maintenance and sustained proliferation, a significant population of cancers (10-15%) employs telomerase-independent strategies, collectively dubbed Alternative Lengthening of Telomeres (ALT). Most ALT cells relax the usual role of telomeres as inhibitors of local homologous recombination while maintaining the ability of telomeres to prohibit local non-homologous end joining reactions. Here we review current concepts surrounding how ALT telomeres achieve this new balance via alterations in chromatin landscape, DNA damage repair processes and handling of telomeric transcription. We also discuss telomerase independent end maintenance strategies utilized by other organisms, including fruitflies and yeasts, to draw parallels and contrasts and highlight additional modes, beyond ALT, that may be available to telomerase-minus cancers. We conclude by commenting on promises and challenges in the development of effective anti-ALT cancer therapies.
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Affiliation(s)
- Manasi S Apte
- a Laboratory of Biochemistry and Molecular Biology , Center for Cancer Research, National Cancer Institute, NIH , Bethesda , MD , USA
| | - Julia Promisel Cooper
- a Laboratory of Biochemistry and Molecular Biology , Center for Cancer Research, National Cancer Institute, NIH , Bethesda , MD , USA
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20
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Simon MN, Churikov D, Géli V. Replication stress as a source of telomere recombination during replicative senescence in Saccharomyces cerevisiae. FEMS Yeast Res 2016; 16:fow085. [PMID: 27683094 DOI: 10.1093/femsyr/fow085] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/27/2016] [Indexed: 12/25/2022] Open
Abstract
Replicative senescence is triggered by short unprotected telomeres that arise in the absence of telomerase. In addition, telomeres are known as difficult regions to replicate due to their repetitive G-rich sequence prone to secondary structures and tightly bound non-histone proteins. Here we review accumulating evidence that telomerase inactivation in yeast immediately unmasks the problems associated with replication stress at telomeres. Early after telomerase inactivation, yeast cells undergo successive rounds of stochastic DNA damages and become dependent on recombination for viability long before the bulk of telomeres are getting critically short. The switch from telomerase to recombination to repair replication stress-induced damage at telomeres creates telomere instability, which may drive further genomic alterations and prepare the ground for telomerase-independent immortalization observed in yeast survivors and in 15% of human cancer.
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Affiliation(s)
- Marie-Noëlle Simon
- Centre de Recherche en Cancérologie de Marseille, 'Equipe labellisée Ligue Contre le Cancer', Inserm U1068, Marseille F-13009, France; CNRS, UMR7258, Marseille F-13009; Institut Paoli-Calmettes, Marseille F-13009, France; Aix-Marseille University, UM 105, Marseille F-13284, France
| | - Dmitri Churikov
- Centre de Recherche en Cancérologie de Marseille, 'Equipe labellisée Ligue Contre le Cancer', Inserm U1068, Marseille F-13009, France; CNRS, UMR7258, Marseille F-13009; Institut Paoli-Calmettes, Marseille F-13009, France; Aix-Marseille University, UM 105, Marseille F-13284, France
| | - Vincent Géli
- Centre de Recherche en Cancérologie de Marseille, 'Equipe labellisée Ligue Contre le Cancer', Inserm U1068, Marseille F-13009, France; CNRS, UMR7258, Marseille F-13009; Institut Paoli-Calmettes, Marseille F-13009, France; Aix-Marseille University, UM 105, Marseille F-13284, France
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21
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Lue NF, Yu EY. Telomere recombination pathways: tales of several unhappy marriages. Curr Genet 2016; 63:401-409. [PMID: 27666406 DOI: 10.1007/s00294-016-0653-8] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2016] [Revised: 09/19/2016] [Accepted: 09/21/2016] [Indexed: 01/29/2023]
Abstract
All happy families are alike; each unhappy family is unhappy in its own way.-Leo Tolstoy, Anna Karenina.
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Affiliation(s)
- Neal F Lue
- Department of Microbiology and Immunology, W. R. Hearst Microbiology Research Center, Weill Cornell Medicine, New York, NY, USA. .,Meyer Cancer Center, Weill Cornell Medicine, New York, NY, USA.
| | - Eun Young Yu
- Department of Microbiology and Immunology, W. R. Hearst Microbiology Research Center, Weill Cornell Medicine, New York, NY, USA
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22
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Markiewicz-Potoczny M, Lydall D. Costs, benefits and redundant mechanisms of adaption to chronic low-dose stress in yeast. Cell Cycle 2016; 15:2732-41. [PMID: 27628486 PMCID: PMC5053569 DOI: 10.1080/15384101.2016.1218104] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
All organisms live in changeable, stressful environments. It has been reported that exposure to low-dose stresses or poisons can improve fitness. However, examining the effects of chronic low-dose chemical exposure is challenging. To address this issue we used temperature sensitive mutations affecting the yeast cell division cycle to induce low-dose stress for 40 generation times, or more. We examined cdc13-1 mutants, defective in telomere function, and cdc15-2 mutants, defective in mitotic kinase activity. We found that each stress induced similar adaptive responses. Stress-exposed cells became resistant to higher levels of stress but less fit, in comparison with unstressed cells, in conditions of low stress. The costs and benefits of adaptation to chronic stress were reversible. In the cdc13-1 context we tested the effects of Rad9, a central player in the response to telomere defects, Exo1, a nuclease that degrades defective telomeres, and Msn2 and Msn4, 2 transcription factors that contribute to the environmental stress response. We also observed, as expected, that Rad9 and Exo1 modulated the response of cells to stress. In addition we observed that adaptation to stress could still occur in these contexts, with associated costs and benefits. We conclude that functionally redundant cellular networks control the adaptive responses to low dose chronic stress. Our data suggests that if organisms adapt to low dose stress it is helpful if stress continues or increases but harmful should stress levels reduce.
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Affiliation(s)
- Marta Markiewicz-Potoczny
- a Institute for Cell and Molecular Biosciences, The Medical School , Newcastle University , Newcastle upon Tyne , UK
| | - David Lydall
- a Institute for Cell and Molecular Biosciences, The Medical School , Newcastle University , Newcastle upon Tyne , UK
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23
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Ivanova IG, Maringele L. Polymerases ε and ∂ repair dysfunctional telomeres facilitated by salt. Nucleic Acids Res 2016; 44:3728-38. [PMID: 26883631 PMCID: PMC4856982 DOI: 10.1093/nar/gkw071] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2015] [Accepted: 02/01/2016] [Indexed: 12/19/2022] Open
Abstract
Damaged DNA can be repaired by removal and re-synthesis of up to 30 nucleotides during base or nucleotide excision repair. An important question is what happens when many more nucleotides are removed, resulting in long single-stranded DNA (ssDNA) lesions. Such lesions appear on chromosomes during telomere damage, double strand break repair or after the UV damage of stationary phase cells. Here, we show that long single-stranded lesions, formed at dysfunctional telomeres in budding yeast, are re-synthesized when cells are removed from the telomere-damaging environment. This process requires Pol32, an accessory factor of Polymerase δ. However, re-synthesis takes place even when the telomere-damaging conditions persist, in which case the accessory factors of both polymerases δ and ε are required, and surprisingly, salt. Salt added to the medium facilitates the DNA synthesis, independently of the osmotic stress responses. These results provide unexpected insights into the DNA metabolism and challenge the current view on cellular responses to telomere dysfunction.
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Affiliation(s)
- Iglika G Ivanova
- Institute for Cell and Molecular Biosciences (ICaMB), Newcastle University, Newcastle upon Tyne, NE2 44H, UK
| | - Laura Maringele
- Institute for Cell and Molecular Biosciences (ICaMB), Newcastle University, Newcastle upon Tyne, NE2 44H, UK
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24
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Mersaoui SY, Gravel S, Karpov V, Wellinger RJ. DNA damage checkpoint adaptation genes are required for division of cells harbouring eroded telomeres. MICROBIAL CELL 2015; 2:394-405. [PMID: 28357265 PMCID: PMC5354583 DOI: 10.15698/mic2015.10.229] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
In budding yeast, telomerase and the Cdc13p protein are two key players acting to ensure telomere stability. In the absence of telomerase, cells eventually enter a growth arrest which only few can overcome via a conserved process; such cells are called survivors. Survivors rely on homologous recombination-dependent mechanisms for telomeric repeat addition. Previously, we showed that such survivor cells also manage to bypass the loss of the essential Cdc13p protein to give rise to Cdc13-independent (or cap-independent) strains. Here we show that Cdc13-independent cells grow with persistently recognized DNA damage, which does not however result in a checkpoint activation; thus no defect in cell cycle progression is detectable. The absence of checkpoint signalling rather is due to the accumulation of mutations in checkpoint genes such as RAD24 or MEC1. Importantly, our results also show that cells that have lost the ability to adapt to persistent DNA damage, also are very much impaired in generating cap-independent cells. Altogether, these results show that while the capping process can be flexible, it takes a very specific genetic setup to allow a change from canonical capping to alternative capping. We hypothesize that in the alternative capping mode, genome integrity mechanisms are abrogated, which could cause increased mutation frequencies. These results from yeast have clear parallels in transformed human cancer cells and offer deeper insights into processes operating in pre-cancerous human cells that harbour eroded telomeres.
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Affiliation(s)
- Sofiane Y Mersaoui
- Dept of Microbiology and Infectious Diseases, Faculty of Medicine and Health Sciences, Université de Sherbrooke, 3201, Rue Jean Mignault, Sherbrooke, J1E 4K8, Canada
| | - Serge Gravel
- Dept of Microbiology and Infectious Diseases, Faculty of Medicine and Health Sciences, Université de Sherbrooke, 3201, Rue Jean Mignault, Sherbrooke, J1E 4K8, Canada
| | - Victor Karpov
- Dept of Microbiology and Infectious Diseases, Faculty of Medicine and Health Sciences, Université de Sherbrooke, 3201, Rue Jean Mignault, Sherbrooke, J1E 4K8, Canada
| | - Raymund J Wellinger
- Dept of Microbiology and Infectious Diseases, Faculty of Medicine and Health Sciences, Université de Sherbrooke, 3201, Rue Jean Mignault, Sherbrooke, J1E 4K8, Canada
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25
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Abstract
The ends of linear chromosomes are capped by nucleoprotein structures called telomeres. A dysfunctional telomere may resemble a DNA double-strand break (DSB), which is a severe form of DNA damage. The presence of one DSB is sufficient to drive cell cycle arrest and cell death. Therefore cells have evolved mechanisms to repair DSBs such as homologous recombination (HR). HR-mediated repair of telomeres can lead to genome instability, a hallmark of cancer cells, which is why such repair is normally inhibited. However, some HR-mediated processes are required for proper telomere function. The need for some recombination activities at telomeres but not others necessitates careful and complex regulation, defects in which can lead to catastrophic consequences. Furthermore, some cell types can maintain telomeres via telomerase-independent, recombination-mediated mechanisms. In humans, these mechanisms are called alternative lengthening of telomeres (ALT) and are used in a subset of human cancer cells. In this review, we summarize the different recombination activities occurring at telomeres and discuss how they are regulated. Much of the current knowledge is derived from work using yeast models, which is the focus of this review, but relevant studies in mammals are also included.
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Affiliation(s)
- Clémence Claussin
- European Research Institute for the Biology of Ageing, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands
| | - Michael Chang
- European Research Institute for the Biology of Ageing, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands
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26
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Two routes to senescence revealed by real-time analysis of telomerase-negative single lineages. Nat Commun 2015; 6:7680. [PMID: 26158780 PMCID: PMC4503340 DOI: 10.1038/ncomms8680] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2015] [Accepted: 05/31/2015] [Indexed: 01/15/2023] Open
Abstract
In eukaryotes, telomeres cap chromosome ends to maintain genomic stability. Failure to maintain telomeres leads to their progressive erosion and eventually triggers replicative senescence, a pathway that protects against unrestricted cell proliferation. However, the mechanisms underlying the variability and dynamics of this pathway are still elusive. Here we use a microfluidics-based live-cell imaging assay to investigate replicative senescence in individual Saccharomyces cerevisiae cell lineages following telomerase inactivation. We characterize two mechanistically distinct routes to senescence. Most lineages undergo an abrupt and irreversible switch from a replicative to an arrested state, consistent with telomeres reaching a critically short length. In contrast, other lineages experience frequent and stochastic reversible arrests, consistent with the repair of accidental telomere damage by Pol32, a subunit of polymerase δ required for break-induced replication and for post-senescence survival. Thus, at the single-cell level, replicative senescence comprises both deterministic cell fates and chaotic cell division dynamics. Erosion of telomeres eventually causes replicative senescence, but mechanisms underlying the variability and dynamics of the pathway are not known. Here, the authors examine senescence in single yeast cells with inactivated telomerase to reveal two mechanistically distinct routes to senescence.
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28
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Grandin N, Charbonneau M. RPA provides checkpoint-independent cell cycle arrest and prevents recombination at uncapped telomeres of Saccharomyces cerevisiae. DNA Repair (Amst) 2013; 12:212-26. [DOI: 10.1016/j.dnarep.2012.12.002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2012] [Revised: 11/13/2012] [Accepted: 12/08/2012] [Indexed: 12/23/2022]
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29
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Abstract
The mechanisms that maintain the stability of chromosome ends have broad impact on genome integrity in all eukaryotes. Budding yeast is a premier organism for telomere studies. Many fundamental concepts of telomere and telomerase function were first established in yeast and then extended to other organisms. We present a comprehensive review of yeast telomere biology that covers capping, replication, recombination, and transcription. We think of it as yeast telomeres—soup to nuts.
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Chang M, Dittmar JC, Rothstein R. Long telomeres are preferentially extended during recombination-mediated telomere maintenance. Nat Struct Mol Biol 2011; 18:451-6. [PMID: 21441915 PMCID: PMC3071861 DOI: 10.1038/nsmb.2034] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2010] [Accepted: 01/20/2011] [Indexed: 01/01/2023]
Abstract
Most human somatic cells do not express telomerase. Consequently, with each cell division their telomeres progressively shorten until replicative senescence is induced. Approximately 15% of human cancers maintain their telomeres using telomerase-independent, recombination-based mechanisms collectively termed Alternative Lengthening of Telomeres (ALT). In the yeast Saccharomyces cerevisiae, ALT cells are referred to as “survivors”. One type of survivor (type II) resembles human ALT cells in that both are defined by the amplification of telomeric repeats. We analyzed recombination-mediated telomere extension events at individual telomeres in telomerase-negative yeast during type II survivor formation and find that long telomeres are preferentially extended. Furthermore, we find that senescent cells with long telomeres are more efficient at bypassing senescence via the type II pathway. We speculate that telomere length may be important in determining whether cancer cells utilize telomerase or ALT to bypass replicative senescence.
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Affiliation(s)
- Michael Chang
- Department of Genetics and Development, Columbia University Medical Center, New York, New York, USA.
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31
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Recombination can cause telomere elongations as well as truncations deep within telomeres in wild-type Kluyveromyces lactis cells. EUKARYOTIC CELL 2010; 10:226-36. [PMID: 21148753 DOI: 10.1128/ec.00209-10] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In this study, we examined the role of recombination at the telomeres of the yeast Kluyveromyces lactis. We demonstrated that an abnormally long and mutationally tagged telomere was subject to high rates of telomere rapid deletion (TRD) that preferentially truncated the telomere to near-wild-type size. Unlike the case in Saccharomyces cerevisiae, however, there was not a great increase in TRD in meiosis. About half of mitotic TRD events were associated with deep turnover of telomeric repeats, suggesting that telomeres were often cleaved to well below normal length prior to being reextended by telomerase. Despite its high rate of TRD, the long telomere showed no increase in the rate of subtelomeric gene conversion, a highly sensitive test of telomere dysfunction. We also showed that the long telomere was subject to appreciable rates of becoming elongated substantially further through a recombinational mechanism that added additional tagged repeats. Finally, we showed that the deep turnover that occurs within normal-length telomeres was diminished in the absence of RAD52. Taken together, our results suggest that homologous recombination is a significant process acting on both abnormally long and normally sized telomeres in K. lactis.
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Pif1- and Exo1-dependent nucleases coordinate checkpoint activation following telomere uncapping. EMBO J 2010; 29:4020-34. [PMID: 21045806 PMCID: PMC3020640 DOI: 10.1038/emboj.2010.267] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2010] [Accepted: 09/29/2010] [Indexed: 11/16/2022] Open
Abstract
In the absence of the telomere capping protein Cdc13, budding yeast telomeres erode, resulting in checkpoint arrest. This study shows that the helicase Pif1, known as a telomerase inhibitor, also has a direct role in the resection of uncapped telomeres, acting in parallel to the nuclease Exo1. Essential telomere ‘capping' proteins act as a safeguard against ageing and cancer by inhibiting the DNA damage response (DDR) and regulating telomerase recruitment, thus distinguishing telomeres from double-strand breaks (DSBs). Uncapped telomeres and unrepaired DSBs can both stimulate a potent DDR, leading to cell cycle arrest and cell death. Using the cdc13-1 mutation to conditionally ‘uncap' telomeres in budding yeast, we show that the telomere capping protein Cdc13 protects telomeres from the activity of the helicase Pif1 and the exonuclease Exo1. Our data support a two-stage model for the DDR at uncapped telomeres; Pif1 and Exo1 resect telomeric DNA <5 kb from the chromosome end, stimulating weak checkpoint activation; resection is extended >5 kb by Exo1 and full checkpoint activation occurs. Cdc13 is also crucial for telomerase recruitment. However, cells lacking Cdc13, Pif1 and Exo1, do not senesce and maintain their telomeres in a manner dependent upon telomerase, Ku and homologous recombination. Thus, attenuation of the DDR at uncapped telomeres can circumvent the need for otherwise-essential telomere capping proteins.
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Survival and growth of yeast without telomere capping by Cdc13 in the absence of Sgs1, Exo1, and Rad9. PLoS Genet 2010; 6:e1001072. [PMID: 20808892 PMCID: PMC2924318 DOI: 10.1371/journal.pgen.1001072] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2010] [Accepted: 07/15/2010] [Indexed: 11/19/2022] Open
Abstract
Maintenance of telomere capping is absolutely essential to the survival of eukaryotic cells. Telomere capping proteins, such as Cdc13 and POT1, are essential for the viability of budding yeast and mammalian cells, respectively. Here we identify, for the first time, three genetic modifications that allow budding yeast cells to survive without telomere capping by Cdc13. We found that simultaneous inactivation of Sgs1, Exo1, and Rad9, three DNA damage response (DDR) proteins, is sufficient to allow cell division in the absence of Cdc13. Quantitative amplification of ssDNA (QAOS) was used to show that the RecQ helicase Sgs1 plays an important role in the resection of uncapped telomeres, especially in the absence of checkpoint protein Rad9. Strikingly, simultaneous deletion of SGS1 and the nuclease EXO1, further reduces resection at uncapped telomeres and together with deletion of RAD9 permits cell survival without CDC13. Pulsed-field gel electrophoresis studies show that cdc13-1 rad9Δ sgs1Δ exo1Δ strains can maintain linear chromosomes despite the absence of telomere capping by Cdc13. However, with continued passage, the telomeres of such strains eventually become short and are maintained by recombination-based mechanisms. Remarkably, cdc13Δ rad9Δ sgs1Δ exo1Δ strains, lacking any Cdc13 gene product, are viable and can grow indefinitely. Our work has uncovered a critical role for RecQ helicases in limiting the division of cells with uncapped telomeres, and this may provide one explanation for increased tumorigenesis in human diseases associated with mutations of RecQ helicases. Our results reveal the plasticity of the telomere cap and indicate that the essential role of telomere capping is to counteract specific aspects of the DDR. The telomeric DNA of most eukaryotes consists of G-rich repetitive DNA with a 3′ single stranded DNA (ssDNA) overhang. In human and budding yeast (Saccharomyces cerevisiae) cells, the 3′ ssDNA overhang is bound by essential telomere capping proteins, POT1 and Cdc13 respectively. Maintenance of telomere capping is essential for the survival of cells. The RecQ helicases are a family of highly conserved proteins involved in the maintenance of telomere and genome stability. Loss of function of three RecQ helicases in humans results in cancer predisposition disorders Bloom's syndrome (BS), Werner's syndrome (WS), and Rothmund Thomson syndrome (RTS). Here we found that the RecQ helicase in budding yeast, Sgs1, plays a critical role in the resection of uncapped telomeres. Strikingly, simultaneous inactivation of Sgs1, the exonuclease Exo1, and checkpoint protein Rad9 allows budding yeast cells to divide in the absence of Cdc13, indicating that the essential role of the telomere cap is to counteract specific components of DNA damage response pathways. We speculate that, in certain genetic contexts, mammalian RecQ helicase also inhibit growth of cells with telomere capping defects, and a defect in this role could contribute to increased levels of tumorigenesis in BS, WS, and RTS patients.
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Wellinger RJ. When the caps fall off: responses to telomere uncapping in yeast. FEBS Lett 2010; 584:3734-40. [PMID: 20600003 DOI: 10.1016/j.febslet.2010.06.031] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2010] [Revised: 06/18/2010] [Accepted: 06/21/2010] [Indexed: 12/25/2022]
Abstract
Telomeres protect the ends of linear chromosomes from activities that cause sequence losses or challenge chromosome integrity. Furthermore, these ends must be hidden from detection by the DNA damage recognition and response pathways. In particular, they must not fuse with each other. These fundamental and very first functions attributed to telomeres are also summarized with the term 'chromosome capping'. However, telomeres can become uncapped and the foremost cellular responses to such events aim to restore genome stability in the most conservative fashion possible. I will provide an outline of cellular responses to uncapping in budding yeast and briefly discuss the reverse, namely avoidance mechanisms that prevent telomere formation at inappropriate places.
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Affiliation(s)
- Raymund J Wellinger
- Department of Microbiology and Infectious Diseases, Faculty of Medicine, Université de Sherbrooke, Sherbrooke, Quebec, Canada.
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35
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Watson JM, Riha K. Comparative biology of telomeres: where plants stand. FEBS Lett 2010; 584:3752-9. [PMID: 20580356 PMCID: PMC3767043 DOI: 10.1016/j.febslet.2010.06.017] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2010] [Revised: 06/11/2010] [Accepted: 06/14/2010] [Indexed: 01/02/2023]
Abstract
Telomeres are essential structures at the ends of eukaryotic chromosomes. Work on their structure and function began almost 70 years ago in plants and flies, continued through the Nobel Prize winning work on yeast and ciliates, and goes on today in many model and non-model organisms. The basic molecular mechanisms of telomeres are highly conserved throughout evolution, and our current understanding of how telomeres function is a conglomeration of insights gained from many different species. This review will compare the current knowledge of telomeres in plants with other organisms, with special focus on the functional length of telomeric DNA, the search for TRF homologs, the family of POT1 proteins, and the recent discovery of members of the CST complex.
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Affiliation(s)
- J Matthew Watson
- Gregor Mendel Institute of Molecular Plant Biology, Austrian Academy of Sciences, Vienna, Austria
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36
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Eckert-Boulet N, Lisby M. Regulation of homologous recombination at telomeres in budding yeast. FEBS Lett 2010; 584:3696-702. [DOI: 10.1016/j.febslet.2010.05.037] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2010] [Revised: 05/14/2010] [Accepted: 05/17/2010] [Indexed: 10/19/2022]
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37
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Taming the tiger by the tail: modulation of DNA damage responses by telomeres. EMBO J 2009; 28:2174-87. [PMID: 19629039 PMCID: PMC2722249 DOI: 10.1038/emboj.2009.176] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2009] [Accepted: 06/03/2009] [Indexed: 11/09/2022] Open
Abstract
Telomeres are by definition stable and inert chromosome ends, whereas internal chromosome breaks are potent stimulators of the DNA damage response (DDR). Telomeres do not, as might be expected, exclude DDR proteins from chromosome ends but instead engage with many DDR proteins. However, the most powerful DDRs, those that might induce chromosome fusion or cell-cycle arrest, are inhibited at telomeres. In budding yeast, many DDR proteins that accumulate most rapidly at double strand breaks (DSBs), have important functions in physiological telomere maintenance, whereas DDR proteins that arrive later tend to have less important functions. Considerable diversity in telomere structure has evolved in different organisms and, perhaps reflecting this diversity, different DDR proteins seem to have distinct roles in telomere physiology in different organisms. Drawing principally on studies in simple model organisms such as budding yeast, in which many fundamental aspects of the DDR and telomere biology have been established; current views on how telomeres harness aspects of DDR pathways to maintain telomere stability and permit cell-cycle division are discussed.
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38
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Alberghina L, Coccetti P, Orlandi I. Systems biology of the cell cycle of Saccharomyces cerevisiae: From network mining to system-level properties. Biotechnol Adv 2009; 27:960-978. [PMID: 19465107 DOI: 10.1016/j.biotechadv.2009.05.021] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Following a brief description of the operational procedures of systems biology (SB), the cell cycle of budding yeast is discussed as a successful example of a top-down SB analysis. After the reconstruction of the steps that have led to the identification of a sizer plus timer network in the G1 to S transition, it is shown that basic functions of the cell cycle (the setting of the critical cell size and the accuracy of DNA replication) are system-level properties, detected only by integrating molecular analysis with modelling and simulation of their underlying networks. A detailed network structure of a second relevant regulatory step of the cell cycle, the exit from mitosis, derived from extensive data mining, is constructed and discussed. To reach a quantitative understanding of how nutrients control, through signalling, metabolism and transcription, cell growth and cycle is a very relevant aim of SB. Since we know that about 900 gene products are required for cell cycle execution and control in budding yeast, it is quite clear that a purely systematic approach would require too much time. Therefore lines for a modular SB approach, which prioritises molecular and computational investigations for faster cell cycle understanding, are proposed. The relevance of the insight coming from the cell cycle SB studies in developing a new framework for tackling very complex biological processes, such as cancer and aging, is discussed.
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Affiliation(s)
- Lilia Alberghina
- Department of Biotechnology and Biosciences, University of Milano-Bicocca, P.zza della Scienza 2, 20126 Milano, Italy.
| | - Paola Coccetti
- Department of Biotechnology and Biosciences, University of Milano-Bicocca, P.zza della Scienza 2, 20126 Milano, Italy
| | - Ivan Orlandi
- Department of Biotechnology and Biosciences, University of Milano-Bicocca, P.zza della Scienza 2, 20126 Milano, Italy
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Telomere maintenance and survival in saccharomyces cerevisiae in the absence of telomerase and RAD52. Genetics 2009; 182:671-84. [PMID: 19380905 DOI: 10.1534/genetics.109.102939] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Telomeres are essential features of linear genomes that are crucial for chromosome stability. Telomeric DNA is usually replenished by telomerase. Deletion of genes encoding telomerase components leads to telomere attrition with each cycle of DNA replication, eventually causing cell senescence or death. In the Saccharomyces cerevisiae strain W303, telomerase-null populations bypass senescence and, unless EXO1 is also deleted, this survival is RAD52 dependent. Unexpectedly, we found that the S. cerevisiae strain S288C could survive the removal of RAD52 and telomerase at a low frequency without additional gene deletions. These RAD52-independent survivors were propagated stably and exhibited a telomere organization typical of recombination between telomeric DNA tracts, and in diploids behaved as a multigenic trait. The polymerase-delta subunit Pol32 was dispensable for the maintenance of RAD52-independent survivors. The incidence of this rare escape was not affected by deletion of other genes necessary for RAD52-dependent survival, but correlated with initial telomere length. If W303 strains lacking telomerase and RAD52 first underwent telomere elongation, rare colonies could then bypass senescence. We suggest that longer telomeres provide a more proficient substrate for a novel telomere maintenance mechanism that does not rely on telomerase, RAD52, or POL32.
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40
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Gunisova S, Elboher E, Nosek J, Gorkovoy V, Brown Y, Lucier JF, Laterreur N, Wellinger RJ, Tzfati Y, Tomaska L. Identification and comparative analysis of telomerase RNAs from Candida species reveal conservation of functional elements. RNA (NEW YORK, N.Y.) 2009; 15:546-559. [PMID: 19223441 PMCID: PMC2661832 DOI: 10.1261/rna.1194009] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/28/2008] [Accepted: 12/16/2008] [Indexed: 05/27/2023]
Abstract
The RNA component of telomerase (telomerase RNA; TER) varies substantially both in sequence composition and size (from approximately 150 nucleotides [nt] to >1500 nt) across species. This dramatic divergence has hampered the identification of TER genes and a large-scale comparative analysis of TER sequences and structures among distantly related species. To identify by phylogenetic analysis conserved sequences and structural features of TER that are of general importance, it is essential to obtain TER sequences from evolutionarily distant groups of species, providing enough conservation within each group and enough variation among the groups. To this end, we identified TER genes in several yeast species with relatively large (>20 base pairs) and nonvariant telomeric repeats, mostly from the genus Candida. Interestingly, several of the TERs reported here are longer than all other yeast TERs known to date. Within these TERs, we predicted a pseudoknot containing U-A.U base triples (conserved in vertebrates, budding yeasts, and ciliates) and a three-way junction element (conserved in vertebrates and budding yeasts). In addition, we identified a novel conserved sequence (CS2a) predicted to reside within an internal-loop structure, in all the budding yeast TERs examined. CS2a is located near the Est1p-binding bulge-stem previously identified in Saccharomyces cerevisiae. Mutational analyses in both budding yeasts S. cerevisiae and Kluyveromyces lactis demonstrate that CS2a is essential for in vivo telomerase function. The comparative and mutational analyses of conserved TER elements reported here provide novel insights into the structure and function of the telomerase ribonucleoprotein complex.
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Telomerase- and Rad52-independent immortalization of budding yeast by an inherited-long-telomere pathway of telomeric repeat amplification. Mol Cell Biol 2008; 29:965-85. [PMID: 19047370 DOI: 10.1128/mcb.00817-08] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In the absence of telomerase, telomeres erode, provoking accumulation of DNA damage and death by senescence. Rare survivors arise, however, due to Rad52-based amplification of telomeric sequences by homologous recombination. The present study reveals that in budding yeast cells, postsenescence survival relying on amplification of the TG(1-3) telomeric repeats can take place in the absence of Rad52 when overelongated telomeres are present during senescence (hence its designation ILT, for inherited-long-telomere, pathway). By growth competition, the Rad52-independent pathway was almost as efficient as the Rad51- and Rad52-dependent pathway that predominates in telomerase-negative cells. The ILT pathway could also be triggered by increased telomerase accessibility before telomerase removal, combined with loss of telomere protection, indicating that prior accumulation of recombination proteins was not required. The ILT pathway was dependent on Rad50 and Mre11 but not on the Rad51 recombinase and Rad59, thus making it distinct from both the type II (budding yeast ALT [alternative lengthening of telomeres]) and type I pathways amplifying the TG(1-3) repeats and subtelomeric sequences, respectively. The ILT pathway also required the Rad1 endonuclease and Elg1, a replication factor C (RFC)-like complex subunit, but not Rad24 or Ctf18 (two subunits of two other RFC-like complexes), the Dnl4 ligase, Yku70, or Nej1. Possible mechanisms for this Rad52-independent pathway of telomeric repeat amplification are discussed. The effects of inherited long telomeres on Rad52-dependent recombination are also reported.
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Bergeron J, Drouin G. The evolution of 5S ribosomal RNA genes linked to the rDNA units of fungal species. Curr Genet 2008; 54:123-31. [PMID: 18704425 DOI: 10.1007/s00294-008-0201-2] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2008] [Revised: 06/05/2008] [Accepted: 06/08/2008] [Indexed: 11/27/2022]
Abstract
5S ribosomal RNA (rRNA) genes are known to move in and out of various tandemly repeated eukaryotic gene families during evolution. Here, we investigated the organization of 5S rRNA genes linked to the ribosomal DNA (rDNA) units in 147 fungal species using available sequence and genome databanks. Whereas some fungal species have no 5S rRNA genes in their rDNA units, others have one or two 5S rRNA copies linked on the same or the opposite strand. There were at least 13 independent changes during the evolution of fungal species. These include two 5S rRNA genes loss, five 5S rRNA genes inversions and six 5S rRNA genes insertions (including duplications). The lower frequency of 5S rRNA genes loss might be due to the fact that these events are more likely to affect fitness. The maximum time required for 5S rRNA gene organization to change between related species was estimated to be 7.5 millions years based on the sequences of the elongation factor alpha genes of Candida glabrata and Saccharomyces mikatae. This time is much longer than the homogenization time predicted from theoretical and experimental studies and likely reflects the lack of closely related species or strains in our data set.
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Affiliation(s)
- Julie Bergeron
- Département de Biologie et Centre de Recherche Avancée en Génomique Environnementale, Université d'Ottawa, 30 Marie Curie, Ottawa, ON, Canada K1N 6N5
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The telotype defines the telomere state in Saccharomyces cerevisiae and is inherited as a dominant non-Mendelian characteristic in cells lacking telomerase. Genetics 2008; 178:245-57. [PMID: 18202371 DOI: 10.1534/genetics.107.083030] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Telomeres are an unusual component of the genome because they do not encode genes, but their structure and cellular maintenance machinery (which we define as "telotype") are essential for chromosome stability. Cells can switch between different phenotypic states. One such example is when they switch from maintenance mediated by telomerase (TERT telotype) to one of the two alternative mechanisms of telomere preservation (ALT I and ALT II telotype). The nature of this switch is largely unknown. Reintroduction of telomerase into ALT II, but not ALT I, yeast led to the loss of their ability to survive a second round of telomerase withdrawal. Mating-based genetic analysis of ALT I and II revealed that both types of telomerase-independent telomere maintenance are inherited as a non-Mendelian trait dominant over senescence (SEN telotype). Additionally, inheritance of ALT I and ALT II did not depend on either the mitochondrial genome or a prion-based mechanism. Type I, but not type II, survivor cells exhibited impaired gene silencing, potentially connecting the switch to the ALT telotype epigenetic changes. These data provide evidence that nonprion epigenetic-like mechanisms confer flexibility on cells as a population to adjust to the life-threatening situation of telomerase loss, allowing cells to switch from TERT to ALT telotypes that can sustain viable populations.
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Abstract
The ends of eukaryotic chromosomes have long been defined as structures that must avoid being detected as DNA breaks. They are protected from checkpoints, homologous recombination, end-to-end fusions, or other events that normally promote repair of intrachromosomal DNA breaks. This differentiation is thought to be the consequence of a unique organization of chromosomal ends into specialized nucleoprotein complexes called telomeres. However, it is becoming increasingly clear that proteins governing the DNA damage response are intimately involved in the regulation of telomeres, which undergo processing and structural changes that elicit a transient DNA damage response. This suggests that functional telomeres can be recognized as DNA breaks during a temporally limited window, indicating that the difference between a break and a telomere is less defined than previously assumed.
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Affiliation(s)
- Maria Pia Longhese
- Dipartimento di Biotecnologie e Bioscienze, Università di Milano-Bicocca, Milan, Italy.
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45
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Cohen S, Houben A, Segal D. Extrachromosomal circular DNA derived from tandemly repeated genomic sequences in plants. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2008; 53:1027-1034. [PMID: 18088310 DOI: 10.1111/j.1365-313x.2007.03394.x] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Extrachromosomal circular DNA (eccDNA) is one characteristic of the plasticity of the eukaryotic genome. It was found in various non-plant organisms from yeast to humans. EccDNA is heterogeneous in size and contains sequences derived primarily from repetitive chromosomal DNA. Here, we report the occurrence of eccDNA in small and large genome plant species, as identified using two-dimensional gel electrophoresis. We show that eccDNA is readily detected in both Arabidopsis thaliana and Brachycome dichromosomatica, reflecting a normal phenomenon that occurs in wild-type plants. The size of plant eccDNA ranges from > 2 kb to < 20 kb, which is similar to the sizes found in other organisms. These DNA molecules correspond to 5S ribosomal DNA (rDNA), non-coding chromosomal high-copy tandem repeats and telomeric DNA of both species. Circular multimers of the repeating unit of 5S rDNA were identified in both species. In addition, similar multimers were also demonstrated with the B. dichromosomatica repetitive element Bdm29. Such circular multimers of tandem repeats were found in animal models, suggesting a common mechanism for eccDNA formation among eukaryotes. This mechanism may involve looping-out via intrachromosomal homologous recombination. The implications of these results on genome plasticity and evolutionary processes are discussed.
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Affiliation(s)
- Sarit Cohen
- Department of Molecular Microbiology and Biotechnology, Tel Aviv University, Tel Aviv, Israel.
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46
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Grandin N, Charbonneau M. Protection against chromosome degradation at the telomeres. Biochimie 2008; 90:41-59. [PMID: 17764802 DOI: 10.1016/j.biochi.2007.07.008] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2007] [Accepted: 07/17/2007] [Indexed: 10/23/2022]
Abstract
Telomeres, the ends of linear chromosomes, contain repeated TG-rich sequences which, in dividing cells, must be constantly replenished in order to avoid chromosome erosion and, hence, genomic instability. Moreover, unprotected telomeres are prone to end-to-end fusions. Telomerase, a specialized reverse transcriptase with a built-in RNA template, or, in the absence of telomerase, alternative pathways of telomere maintenance are required for continuous cell proliferation in actively dividing cells as well as in cancerous cells emerging in deregulated somatic tissues. The challenge is to keep these free DNA ends masked from the nucleolytic attacks that will readily operate on any DNA double-strand break in the cell, while also allowing the recruitment of telomerase at intervals. Specialized telomeric proteins, as well as DNA repair and checkpoint proteins with a dual role in telomere maintenance and DNA damage signaling/repair, protect the telomere ends from degradation and some of them also function in telomerase recruitment or other aspects of telomere length homeostasis. Phosphorylation of some telomeric proteins by checkpoint protein kinases appears to represent a mode of regulation of telomeric mechanisms. Finally, recent studies have allowed starting to understand the coupling between progression of the replication forks through telomeric regions and the subsequent telomere replication by telomerase, as well as retroaction of telomerase in cis on the firing of nearby replication origins.
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Affiliation(s)
- Nathalie Grandin
- UMR CNRS no. 5239, Ecole Normale Supérieure de Lyon, IFR128 BioSciences Gerland-Lyon Sud, 46, allée d'Italie, 69364 Lyon, France
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Cesare AJ, Reddel RR. Telomere uncapping and alternative lengthening of telomeres. Mech Ageing Dev 2007; 129:99-108. [PMID: 18215414 DOI: 10.1016/j.mad.2007.11.006] [Citation(s) in RCA: 91] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2007] [Revised: 11/23/2007] [Accepted: 11/30/2007] [Indexed: 11/17/2022]
Abstract
A substantial number of human tumors utilize a telomerase-independent telomere length maintenance mechanism referred to as alternative lengthening of telomeres (ALT). Although it is known that ALT is a telomere-specific, loss of function phenotype, which involves lengthening of telomeres by homologous recombination-mediated replication of telomeric DNA, many of the details of these processes require elucidation. Here we discuss the current literature on ALT and telomere capping, specifically focusing on how alterations in telomere capping functions may permit activation of ALT and explain the phenotypic characteristics of cells in which this occurs.
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Affiliation(s)
- Anthony J Cesare
- Cancer Research Unit, Children's Medical Research Institute, 214 Hawkesbury Road, Westmead, New South Wales 2145, Australia
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Telomere loops and homologous recombination-dependent telomeric circles in a Kluyveromyces lactis telomere mutant strain. Mol Cell Biol 2007; 28:20-9. [PMID: 17967889 DOI: 10.1128/mcb.01122-07] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The Kluyveromyces lactis ter1-16T strain contains mutant telomeres that are poorly bound by Rap1, resulting in a telomere-uncapping phenotype and significant elongation of the telomeric DNA. The elongated telomeres of ter1-16T allowed the isolation and examination of native yeast telomeric DNA by electron microscopy. In the telomeric DNA isolated from ter1-16T, looped molecules were observed with the physical characteristics of telomere loops (t-loops) previously described in mammalian and plant cells. ter1-16T cells were also found to contain free circular telomeric DNA molecules (t-circles) ranging up to the size of an entire telomere. When the ter1-16T uncapping phenotype was repressed by overexpression of RAP1 or recombination was inhibited by deletion of rad52, the isolated telomeric DNA contained significantly fewer t-loops and t-circles. These results suggest that disruption of Rap1 results in elevated recombination at telomeres, leading to increased strand invasion of the 3' overhang within t-loop junctions and resolution of the t-loop junctions into free t-circles.
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Grudic A, Jul-Larsen A, Haring SJ, Wold MS, Lønning PE, Bjerkvig R, Bøe SO. Replication protein A prevents accumulation of single-stranded telomeric DNA in cells that use alternative lengthening of telomeres. Nucleic Acids Res 2007; 35:7267-78. [PMID: 17959650 PMCID: PMC2175364 DOI: 10.1093/nar/gkm738] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
The activation of a telomere maintenance mechanism is required for cancer development in humans. While most tumors achieve this by expressing the enzyme telomerase, a fraction (5–15%) employs a recombination-based mechanism termed alternative lengthening of telomeres (ALT). Here we show that loss of the single-stranded DNA-binding protein replication protein A (RPA) in human ALT cells, but not in telomerase-positive cells, causes increased exposure of single-stranded G-rich telomeric DNA, cell cycle arrest in G2/M phase, accumulation of single-stranded telomeric DNA within ALT-associated PML bodies (APBs), and formation of telomeric aggregates at the ends of metaphase chromosomes. This study demonstrates differences between ALT cells and telomerase-positive cells in the requirement for RPA in telomere processing and implicates the ALT mechanism in tumor cells as a possible therapeutic target.
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Affiliation(s)
- Amra Grudic
- Section of Oncology, Department of Medicine, Haukeland University Hospital
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The role of Stn1p in Saccharomyces cerevisiae telomere capping can be separated from its interaction with Cdc13p. Genetics 2007; 177:1459-74. [PMID: 17947422 DOI: 10.1534/genetics.107.078840] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The function of telomeres is twofold: to facilitate complete chromosome replication and to protect chromosome ends against fusions and illegitimate recombination. In the budding yeast Saccharomyces cerevisiae, interactions among Cdc13p, Stn1p, and Ten1p are thought to be critical for promoting these processes. We have identified distinct Stn1p domains that mediate interaction with either Ten1p or Cdc13p, allowing analysis of whether the interaction between Cdc13p and Stn1p is indeed essential for telomere capping or length regulation. Consistent with the model that the Stn1p essential function is to promote telomere end protection through Cdc13p, stn1 alleles that truncate the C-terminal 123 residues fail to interact with Cdc13p and do not support viability when expressed at endogenous levels. Remarkably, more extensive deletions that remove an additional 185 C-terminal residues from Stn1p now allow cell growth at endogenous expression levels. The viability of these stn1-t alleles improves with increasing expression level, indicating that increased stn1-t dosage can compensate for the loss of Cdc13p-Stn1p interaction. However, telomere length is misregulated at all expression levels. Thus, an amino-terminal region of Stn1p is sufficient for its essential function, while a central region of Stn1p either negatively regulates the STN1 essential function or destabilizes the mutant Stn1 protein.
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