1
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Premkumar T, Paniker L, Kang R, Biot M, Humphrey E, Destain H, Ferranti I, Okulate I, Nguyen H, Kilaru V, Frasca M, Chakraborty P, Cole F. Genetic dissection of crossover mutants defines discrete intermediates in mouse meiosis. Mol Cell 2023; 83:2941-2958.e7. [PMID: 37595556 PMCID: PMC10469168 DOI: 10.1016/j.molcel.2023.07.022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2022] [Revised: 03/28/2023] [Accepted: 07/21/2023] [Indexed: 08/20/2023]
Abstract
Crossovers (COs), the exchange of homolog arms, are required for accurate chromosome segregation during meiosis. Studies in yeast have described the single-end invasion (SEI) intermediate: a stabilized 3' end annealed with the homolog as the first detectible CO precursor. SEIs are thought to differentiate into double Holliday junctions (dHJs) that are resolved by MutLgamma (MLH1/MLH3) into COs. Currently, we lack knowledge of early steps of mammalian CO recombination or how intermediates are differentiated in any organism. Using comprehensive analysis of recombination in thirteen different genetic conditions with varying levels of compromised CO resolution, we infer CO precursors include asymmetric SEI-like intermediates and dHJs in mouse. In contrast to yeast, MLH3 is structurally required to differentiate CO precursors into dHJs. We verify conservation of aspects of meiotic recombination and show unique features in mouse, providing mechanistic insight into CO formation.
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Affiliation(s)
- Tolkappiyan Premkumar
- Department of Epigenetics and Molecular Carcinogenesis, The University of Texas MD Anderson Cancer Center, Houston, TX, USA; The University of Texas MD Anderson Cancer Center UTHealth Houston Graduate School of Biomedical Sciences, Program in Genetics and Epigenetics, Houston, TX, USA
| | - Lakshmi Paniker
- Department of Epigenetics and Molecular Carcinogenesis, The University of Texas MD Anderson Cancer Center, Houston, TX, USA
| | - Rhea Kang
- Department of Epigenetics and Molecular Carcinogenesis, The University of Texas MD Anderson Cancer Center, Houston, TX, USA; The University of Texas MD Anderson Cancer Center UTHealth Houston Graduate School of Biomedical Sciences, Program in Genetics and Epigenetics, Houston, TX, USA
| | - Mathilde Biot
- Department of Epigenetics and Molecular Carcinogenesis, The University of Texas MD Anderson Cancer Center, Houston, TX, USA
| | - Ericka Humphrey
- Department of Epigenetics and Molecular Carcinogenesis, The University of Texas MD Anderson Cancer Center, Houston, TX, USA
| | - Honorine Destain
- Department of Epigenetics and Molecular Carcinogenesis, The University of Texas MD Anderson Cancer Center, Houston, TX, USA
| | - Isabella Ferranti
- Department of Epigenetics and Molecular Carcinogenesis, The University of Texas MD Anderson Cancer Center, Houston, TX, USA
| | - Iyinyeoluwa Okulate
- Department of Epigenetics and Molecular Carcinogenesis, The University of Texas MD Anderson Cancer Center, Houston, TX, USA
| | - Holly Nguyen
- Department of Epigenetics and Molecular Carcinogenesis, The University of Texas MD Anderson Cancer Center, Houston, TX, USA
| | - Vindhya Kilaru
- Department of Epigenetics and Molecular Carcinogenesis, The University of Texas MD Anderson Cancer Center, Houston, TX, USA
| | - Melissa Frasca
- Department of Epigenetics and Molecular Carcinogenesis, The University of Texas MD Anderson Cancer Center, Houston, TX, USA; The University of Texas MD Anderson Cancer Center UTHealth Houston Graduate School of Biomedical Sciences, Program in Genetics and Epigenetics, Houston, TX, USA
| | - Parijat Chakraborty
- Department of Epigenetics and Molecular Carcinogenesis, The University of Texas MD Anderson Cancer Center, Houston, TX, USA
| | - Francesca Cole
- Department of Epigenetics and Molecular Carcinogenesis, The University of Texas MD Anderson Cancer Center, Houston, TX, USA; The University of Texas MD Anderson Cancer Center UTHealth Houston Graduate School of Biomedical Sciences, Program in Genetics and Epigenetics, Houston, TX, USA.
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2
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Gioia M, Payero L, Salim S, Fajish V. G, Farnaz AF, Pannafino G, Chen JJ, Ajith VP, Momoh S, Scotland M, Raghavan V, Manhart CM, Shinohara A, Nishant KT, Alani E. Exo1 protects DNA nicks from ligation to promote crossover formation during meiosis. PLoS Biol 2023; 21:e3002085. [PMID: 37079643 PMCID: PMC10153752 DOI: 10.1371/journal.pbio.3002085] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2022] [Revised: 05/02/2023] [Accepted: 03/17/2023] [Indexed: 04/21/2023] Open
Abstract
In most sexually reproducing organisms crossing over between chromosome homologs during meiosis is essential to produce haploid gametes. Most crossovers that form in meiosis in budding yeast result from the biased resolution of double Holliday junction (dHJ) intermediates. This dHJ resolution step involves the actions of Rad2/XPG family nuclease Exo1 and the Mlh1-Mlh3 mismatch repair endonuclease. Here, we provide genetic evidence in baker's yeast that Exo1 promotes meiotic crossing over by protecting DNA nicks from ligation. We found that structural elements in Exo1 that interact with DNA, such as those required for the bending of DNA during nick/flap recognition, are critical for its role in crossing over. Consistent with these observations, meiotic expression of the Rad2/XPG family member Rad27 partially rescued the crossover defect in exo1 null mutants, and meiotic overexpression of Cdc9 ligase reduced the crossover levels of exo1 DNA-binding mutants to levels that approached the exo1 null. In addition, our work identified a role for Exo1 in crossover interference. Together, these studies provide experimental evidence for Exo1-protected nicks being critical for the formation of meiotic crossovers and their distribution.
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Affiliation(s)
- Michael Gioia
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York, United States of America
| | - Lisette Payero
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York, United States of America
| | - Sagar Salim
- School of Biology, Indian Institute of Science Education and Research Thiruvananthapuram, Trivandrum, India
| | - Ghanim Fajish V.
- Institute for Protein Research, Osaka University, Suita, Osaka, Japan
| | - Amamah F. Farnaz
- School of Biology, Indian Institute of Science Education and Research Thiruvananthapuram, Trivandrum, India
| | - Gianno Pannafino
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York, United States of America
| | - Jun Jie Chen
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York, United States of America
| | - V. P. Ajith
- School of Biology, Indian Institute of Science Education and Research Thiruvananthapuram, Trivandrum, India
| | - Sherikat Momoh
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York, United States of America
| | - Michelle Scotland
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York, United States of America
| | - Vandana Raghavan
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York, United States of America
| | - Carol M. Manhart
- Department of Chemistry, Temple University, Philadelphia, Pennsylvania, United States of America
| | - Akira Shinohara
- Institute for Protein Research, Osaka University, Suita, Osaka, Japan
| | - K. T. Nishant
- School of Biology, Indian Institute of Science Education and Research Thiruvananthapuram, Trivandrum, India
- Center for High-Performance Computing, Indian Institute of Science Education and Research Thiruvananthapuram, Trivandrum, India
| | - Eric Alani
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York, United States of America
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3
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Wang S, Lee K, Gray S, Zhang Y, Tang C, Morrish RB, Tosti E, van Oers J, Amin MR, Cohen PE, MacCarthy T, Roa S, Scharff MD, Edelmann W, Chahwan R. Role of EXO1 nuclease activity in genome maintenance, the immune response and tumor suppression in Exo1D173A mice. Nucleic Acids Res 2022; 50:8093-8106. [PMID: 35849338 PMCID: PMC9371890 DOI: 10.1093/nar/gkac616] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2021] [Revised: 05/30/2022] [Accepted: 06/30/2022] [Indexed: 11/14/2022] Open
Abstract
DNA damage response pathways rely extensively on nuclease activity to process DNA intermediates. Exonuclease 1 (EXO1) is a pleiotropic evolutionary conserved DNA exonuclease involved in various DNA repair pathways, replication, antibody diversification, and meiosis. But, whether EXO1 facilitates these DNA metabolic processes through its enzymatic or scaffolding functions remains unclear. Here, we dissect the contribution of EXO1 enzymatic versus scaffolding activity by comparing Exo1DA/DA mice expressing a proven nuclease-dead mutant form of EXO1 to entirely EXO1-deficient Exo1−/− and EXO1 wild type Exo1+/+ mice. We show that Exo1DA/DA and Exo1–/– mice are compromised in canonical DNA repair processing, suggesting that the EXO1 enzymatic role is important for error-free DNA mismatch and double-strand break repair pathways. However, in non-canonical repair pathways, EXO1 appears to have a more nuanced function. Next-generation sequencing of heavy chain V region in B cells showed the mutation spectra of Exo1DA/DA mice to be intermediate between Exo1+/+ and Exo1–/– mice, suggesting that both catalytic and scaffolding roles of EXO1 are important for somatic hypermutation. Similarly, while overall class switch recombination in Exo1DA/DA and Exo1–/– mice was comparably defective, switch junction analysis suggests that EXO1 might fulfill an additional scaffolding function downstream of class switching. In contrast to Exo1−/− mice that are infertile, meiosis progressed normally in Exo1DA/DA and Exo1+/+ cohorts, indicating that a structural but not the nuclease function of EXO1 is critical for meiosis. However, both Exo1DA/DA and Exo1–/– mice displayed similar mortality and cancer predisposition profiles. Taken together, these data demonstrate that EXO1 has both scaffolding and enzymatic functions in distinct DNA repair processes and suggest a more composite and intricate role for EXO1 in DNA metabolic processes and disease.
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Affiliation(s)
- Shanzhi Wang
- Department of Cell Biology, Albert Einstein College of Medicine, 1300 Morris Park Avenue, NY 10461, USA.,Current position: Department of Chemistry, University of Arkansas at Little Rock, Little Rock, AR 72204, USA
| | - Kyeryoung Lee
- Department of Cell Biology, Albert Einstein College of Medicine, 1300 Morris Park Avenue, NY 10461, USA
| | - Stephen Gray
- Department of Biomedical Sciences, Cornell University, NY 14853, USA.,Current position: School of Life Sciences, University of Nottingham, Nottingham NG7 2UH, UK
| | - Yongwei Zhang
- Department of Cell Biology, Albert Einstein College of Medicine, 1300 Morris Park Avenue, NY 10461, USA
| | - Catherine Tang
- Department of Applied Mathematics and Statistics, Stony Brook University, Stony Brook, NY, USA
| | - Rikke B Morrish
- Current position: School of Physics and Astronomy, University of Exeter, Exeter EX4 4QD, UK
| | - Elena Tosti
- Department of Cell Biology, Albert Einstein College of Medicine, 1300 Morris Park Avenue, NY 10461, USA
| | - Johanna van Oers
- Department of Cell Biology, Albert Einstein College of Medicine, 1300 Morris Park Avenue, NY 10461, USA
| | - Mohammad Ruhul Amin
- Department of Computer and Information Science, Fordham University, Bronx, NY, USA
| | - Paula E Cohen
- Department of Biomedical Sciences, Cornell University, NY 14853, USA
| | - Thomas MacCarthy
- Department of Applied Mathematics and Statistics, Stony Brook University, Stony Brook, NY, USA
| | - Sergio Roa
- Department of Biochemistry and Genetics, University of Navarra, 31008Pamplona, Spain.,Centro de Investigacion Biomedica en Red de Cancer (CIBERONC), Instituto de Salud Carlos III, Madrid, Spain.,Navarra Institute for Health Research (IdiSNA), Pamplona, Spain
| | - Matthew D Scharff
- Department of Cell Biology, Albert Einstein College of Medicine, 1300 Morris Park Avenue, NY 10461, USA
| | - Winfried Edelmann
- Department of Cell Biology, Albert Einstein College of Medicine, 1300 Morris Park Avenue, NY 10461, USA
| | - Richard Chahwan
- Institute of Experimental Immunology, University of Zurich, Zurich 8057, Switzerland
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4
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Ahuja JS, Harvey CS, Wheeler DL, Lichten M. Repeated strand invasion and extensive branch migration are hallmarks of meiotic recombination. Mol Cell 2021; 81:4258-4270.e4. [PMID: 34453891 PMCID: PMC8541907 DOI: 10.1016/j.molcel.2021.08.003] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2021] [Revised: 07/09/2021] [Accepted: 07/30/2021] [Indexed: 12/19/2022]
Abstract
Currently favored models for meiotic recombination posit that both noncrossover and crossover recombination are initiated by DNA double-strand breaks but form by different mechanisms: noncrossovers by synthesis-dependent strand annealing and crossovers by formation and resolution of double Holliday junctions centered around the break. This dual mechanism hypothesis predicts different hybrid DNA patterns in noncrossover and crossover recombinants. We show that these predictions are not upheld, by mapping with unprecedented resolution parental strand contributions to recombinants at a model locus. Instead, break repair in both noncrossovers and crossovers involves synthesis-dependent strand annealing, often with multiple rounds of strand invasion. Crossover-specific double Holliday junction formation occurs via processes involving branch migration as an integral feature, one that can be separated from repair of the break itself. These findings reveal meiotic recombination to be a highly dynamic process and prompt a new view of the relationship between crossover and noncrossover recombination.
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Affiliation(s)
- Jasvinder S Ahuja
- Laboratory of Biochemistry and Molecular Biology, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892, USA
| | - Catherine S Harvey
- Laboratory of Biochemistry and Molecular Biology, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892, USA
| | - David L Wheeler
- Laboratory of Biochemistry and Molecular Biology, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892, USA
| | - Michael Lichten
- Laboratory of Biochemistry and Molecular Biology, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892, USA.
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5
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Mhaskar AN, Koornneef L, Zelensky AN, Houtsmuller AB, Baarends WM. High Resolution View on the Regulation of Recombinase Accumulation in Mammalian Meiosis. Front Cell Dev Biol 2021; 9:672191. [PMID: 34109178 PMCID: PMC8181746 DOI: 10.3389/fcell.2021.672191] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2021] [Accepted: 04/19/2021] [Indexed: 11/19/2022] Open
Abstract
A distinguishing feature of meiotic DNA double-strand breaks (DSBs), compared to DSBs in somatic cells, is the fact that they are induced in a programmed and specifically orchestrated manner, which includes chromatin remodeling prior to DSB induction. In addition, the meiotic homologous recombination (HR) repair process that follows, is different from HR repair of accidental DSBs in somatic cells. For instance, meiotic HR involves preferred use of the homolog instead of the sister chromatid as a repair template and subsequent formation of crossovers and non-crossovers in a tightly regulated manner. An important outcome of this distinct repair pathway is the pairing of homologous chromosomes. Central to the initial steps in homology recognition during meiotic HR is the cooperation between the strand exchange proteins (recombinases) RAD51 and its meiosis-specific paralog DMC1. Despite our understanding of their enzymatic activity, details on the regulation of their assembly and subsequent molecular organization at meiotic DSBs in mammals have remained largely enigmatic. In this review, we summarize recent mouse data on recombinase regulation via meiosis-specific factors. Also, we reflect on bulk “omics” studies of initial meiotic DSB processing, compare these with studies using super-resolution microscopy in single cells, at single DSB sites, and explore the implications of these findings for our understanding of the molecular mechanisms underlying meiotic HR regulation.
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Affiliation(s)
- Aditya N Mhaskar
- Department of Developmental Biology, Erasmus MC, Rotterdam, Netherlands
| | - Lieke Koornneef
- Department of Developmental Biology, Erasmus MC, Rotterdam, Netherlands.,Oncode Institute, Utrecht, Netherlands
| | - Alex N Zelensky
- Department of Molecular Genetics, Erasmus MC, Rotterdam, Netherlands
| | - Adriaan B Houtsmuller
- Erasmus Optical Imaging Centre, Department of Pathology, Erasmus MC, Rotterdam, Netherlands.,Department of Pathology, Erasmus MC, Rotterdam, Netherlands
| | - Willy M Baarends
- Department of Developmental Biology, Erasmus MC, Rotterdam, Netherlands
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6
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Li Z, Marcel N, Devkota S, Auradkar A, Hedrick SM, Gantz VM, Bier E. CopyCatchers are versatile active genetic elements that detect and quantify inter-homolog somatic gene conversion. Nat Commun 2021; 12:2625. [PMID: 33976171 PMCID: PMC8113449 DOI: 10.1038/s41467-021-22927-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2021] [Accepted: 04/01/2021] [Indexed: 11/08/2022] Open
Abstract
CRISPR-based active genetic elements, or gene-drives, copied via homology-directed repair (HDR) in the germline, are transmitted to progeny at super-Mendelian frequencies. Active genetic elements also can generate widespread somatic mutations, but the genetic basis for such phenotypes remains uncertain. It is generally assumed that such somatic mutations are generated by non-homologous end-joining (NHEJ), the predominant double stranded break repair pathway active in somatic cells. Here, we develop CopyCatcher systems in Drosophila to detect and quantify somatic gene conversion (SGC) events. CopyCatchers inserted into two independent genetic loci reveal unexpectedly high rates of SGC in the Drosophila eye and thoracic epidermis. Focused RNAi-based genetic screens identify several unanticipated loci altering SGC efficiency, one of which (c-MYC), when downregulated, promotes SGC mediated by both plasmid and homologous chromosome-templates in human HEK293T cells. Collectively, these studies suggest that CopyCatchers can serve as effective discovery platforms to inform potential gene therapy strategies.
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Affiliation(s)
- Zhiqian Li
- Section of Cell and Developmental Biology, University of California San Diego, La Jolla, CA, USA
| | - Nimi Marcel
- Section of Molecular Biology, University of California San Diego, La Jolla, CA, USA
- Department of Cellular and Molecular Medicine, University of California San Diego, La Jolla, CA, USA
| | - Sushil Devkota
- Section of Cell and Developmental Biology, University of California San Diego, La Jolla, CA, USA
| | - Ankush Auradkar
- Section of Cell and Developmental Biology, University of California San Diego, La Jolla, CA, USA
| | - Stephen M Hedrick
- Section of Molecular Biology, University of California San Diego, La Jolla, CA, USA
- Department of Cellular and Molecular Medicine, University of California San Diego, La Jolla, CA, USA
| | - Valentino M Gantz
- Section of Cell and Developmental Biology, University of California San Diego, La Jolla, CA, USA
| | - Ethan Bier
- Section of Cell and Developmental Biology, University of California San Diego, La Jolla, CA, USA.
- Tata Institute for Genetics and Society-UCSD, La Jolla, CA, USA.
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7
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Zhao X, Kumari D, Miller CJ, Kim GY, Hayward B, Vitalo AG, Pinto RM, Usdin K. Modifiers of Somatic Repeat Instability in Mouse Models of Friedreich Ataxia and the Fragile X-Related Disorders: Implications for the Mechanism of Somatic Expansion in Huntington's Disease. J Huntingtons Dis 2021; 10:149-163. [PMID: 33579860 PMCID: PMC7990428 DOI: 10.3233/jhd-200423] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Huntington's disease (HD) is one of a large group of human disorders that are caused by expanded DNA repeats. These repeat expansion disorders can have repeat units of different size and sequence that can be located in any part of the gene and, while the pathological consequences of the expansion can differ widely, there is evidence to suggest that the underlying mutational mechanism may be similar. In the case of HD, the expanded repeat unit is a CAG trinucleotide located in exon 1 of the huntingtin (HTT) gene, resulting in an expanded polyglutamine tract in the huntingtin protein. Expansion results in neuronal cell death, particularly in the striatum. Emerging evidence suggests that somatic CAG expansion, specifically expansion occurring in the brain during the lifetime of an individual, contributes to an earlier disease onset and increased severity. In this review we will discuss mouse models of two non-CAG repeat expansion diseases, specifically the Fragile X-related disorders (FXDs) and Friedreich ataxia (FRDA). We will compare and contrast these models with mouse and patient-derived cell models of various other repeat expansion disorders and the relevance of these findings for somatic expansion in HD. We will also describe additional genetic factors and pathways that modify somatic expansion in the FXD mouse model for which no comparable data yet exists in HD mice or humans. These additional factors expand the potential druggable space for diseases like HD where somatic expansion is a significant contributor to disease impact.
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Affiliation(s)
- Xiaonan Zhao
- Laboratory of Cell and Molecular Biology, National Institutes of Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, USA
| | - Daman Kumari
- Laboratory of Cell and Molecular Biology, National Institutes of Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, USA
| | - Carson J Miller
- Laboratory of Cell and Molecular Biology, National Institutes of Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, USA
| | - Geum-Yi Kim
- Laboratory of Cell and Molecular Biology, National Institutes of Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, USA
| | - Bruce Hayward
- Laboratory of Cell and Molecular Biology, National Institutes of Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, USA
| | - Antonia G Vitalo
- Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA, USA.,Department of Neurology, Harvard Medical School, Boston, MA, USA
| | - Ricardo Mouro Pinto
- Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA, USA.,Department of Neurology, Harvard Medical School, Boston, MA, USA.,Program in Medical and Population Genetics, Broad Institute of MIT and Harvard, Cambridge, MA, USA
| | - Karen Usdin
- Laboratory of Cell and Molecular Biology, National Institutes of Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, USA
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8
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Gobbini E, Casari E, Colombo CV, Bonetti D, Longhese MP. The 9-1-1 Complex Controls Mre11 Nuclease and Checkpoint Activation during Short-Range Resection of DNA Double-Strand Breaks. Cell Rep 2020; 33:108287. [DOI: 10.1016/j.celrep.2020.108287] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2020] [Revised: 09/08/2020] [Accepted: 09/28/2020] [Indexed: 12/17/2022] Open
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9
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Yamada S, Hinch AG, Kamido H, Zhang Y, Edelmann W, Keeney S. Molecular structures and mechanisms of DNA break processing in mouse meiosis. Genes Dev 2020; 34:806-818. [PMID: 32354835 PMCID: PMC7263140 DOI: 10.1101/gad.336032.119] [Citation(s) in RCA: 37] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2019] [Accepted: 03/25/2020] [Indexed: 02/06/2023]
Abstract
Exonucleolytic resection, critical to repair double-strand breaks (DSBs) by recombination, is not well understood, particularly in mammalian meiosis. Here, we define structures of resected DSBs in mouse spermatocytes genome-wide at nucleotide resolution. Resection tracts averaged 1100 nt, but with substantial fine-scale heterogeneity at individual hot spots. Surprisingly, EXO1 is not the major 5' → 3' exonuclease, but the DSB-responsive kinase ATM proved a key regulator of both initiation and extension of resection. In wild type, apparent intermolecular recombination intermediates clustered near to but offset from DSB positions, consistent with joint molecules with incompletely invaded 3' ends. Finally, we provide evidence for PRDM9-dependent chromatin remodeling leading to increased accessibility at recombination sites. Our findings give insight into the mechanisms of DSB processing and repair in meiotic chromatin.
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Affiliation(s)
- Shintaro Yamada
- Molecular Biology Program, Memorial Sloan Kettering Cancer Center, New York, New York 10065, USA
- Department of Radiation Genetics, Graduate School of Medicine, Kyoto University, Kyoto 606-8501, Japan
| | - Anjali Gupta Hinch
- Wellcome Centre for Human Genetics, University of Oxford, Oxford OX3 7BN, United Kingdom
| | - Hisashi Kamido
- Molecular Biology Program, Memorial Sloan Kettering Cancer Center, New York, New York 10065, USA
- Department of Radiation Genetics, Graduate School of Medicine, Kyoto University, Kyoto 606-8501, Japan
| | - Yongwei Zhang
- Department of Cell Biology and Department of Genetics, Albert Einstein College of Medicine, Bronx, New York 10461, USA
| | - Winfried Edelmann
- Department of Cell Biology and Department of Genetics, Albert Einstein College of Medicine, Bronx, New York 10461, USA
| | - Scott Keeney
- Molecular Biology Program, Memorial Sloan Kettering Cancer Center, New York, New York 10065, USA
- Howard Hughes Medical Institute, Memorial Sloan Kettering Cancer Center, New York, New York 10065, USA
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10
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Marsolier-Kergoat MC, Khan MM, Schott J, Zhu X, Llorente B. Mechanistic View and Genetic Control of DNA Recombination during Meiosis. Mol Cell 2019; 70:9-20.e6. [PMID: 29625041 DOI: 10.1016/j.molcel.2018.02.032] [Citation(s) in RCA: 56] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2017] [Revised: 12/07/2017] [Accepted: 02/26/2018] [Indexed: 10/17/2022]
Abstract
Meiotic recombination is essential for fertility and allelic shuffling. Canonical recombination models fail to capture the observed complexity of meiotic recombinants. Here, by combining genome-wide meiotic heteroduplex DNA patterns with meiotic DNA double-strand break (DSB) sites, we show that part of this complexity results from frequent template switching during synthesis-dependent strand annealing that yields noncrossovers and from branch migration of double Holliday junction (dHJ)-containing intermediates that mainly yield crossovers. This complexity also results from asymmetric positioning of crossover intermediates relative to the initiating DSB and Msh2-independent conversions promoted by the suspected dHJ resolvase Mlh1-3 as well as Exo1 and Sgs1. Finally, we show that dHJ resolution is biased toward cleavage of the pair of strands containing newly synthesized DNA near the junctions and that this bias can be decoupled from the crossover-biased dHJ resolution. These properties are likely conserved in eukaryotes containing ZMM proteins, which includes mammals.
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Affiliation(s)
- Marie-Claude Marsolier-Kergoat
- CEA/DRF, I2BC/UMR 9198, SBIGeM, Gif-sur-Yvette, France; CNRS-UMR 7206, Éco-anthropologie et Ethnobiologie, Musée de l'Homme, 17, Place du Trocadéro et du 11 Novembre, Paris, France.
| | - Md Muntaz Khan
- Cancer Research Center of Marseille, CNRS UMR7258, INSERM U1068, Institut Paoli-Calmettes, Aix-Marseille Université UM105, Marseille, France
| | - Jonathan Schott
- Cancer Research Center of Marseille, CNRS UMR7258, INSERM U1068, Institut Paoli-Calmettes, Aix-Marseille Université UM105, Marseille, France
| | - Xuan Zhu
- Molecular Biology Program, Memorial Sloan Kettering Cancer Center and Howard Hughes Medical Institute, New York, NY, USA
| | - Bertrand Llorente
- Cancer Research Center of Marseille, CNRS UMR7258, INSERM U1068, Institut Paoli-Calmettes, Aix-Marseille Université UM105, Marseille, France.
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11
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Oh J, Symington LS. Role of the Mre11 Complex in Preserving Genome Integrity. Genes (Basel) 2018; 9:E589. [PMID: 30501098 PMCID: PMC6315862 DOI: 10.3390/genes9120589] [Citation(s) in RCA: 54] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2018] [Revised: 11/26/2018] [Accepted: 11/27/2018] [Indexed: 12/12/2022] Open
Abstract
DNA double-strand breaks (DSBs) are hazardous lesions that threaten genome integrity and cell survival. The DNA damage response (DDR) safeguards the genome by sensing DSBs, halting cell cycle progression and promoting repair through either non-homologous end joining (NHEJ) or homologous recombination (HR). The Mre11-Rad50-Xrs2/Nbs1 (MRX/N) complex is central to the DDR through its structural, enzymatic, and signaling roles. The complex tethers DNA ends, activates the Tel1/ATM kinase, resolves protein-bound or hairpin-capped DNA ends, and maintains telomere homeostasis. In addition to its role at DSBs, MRX/N associates with unperturbed replication forks, as well as stalled replication forks, to ensure complete DNA synthesis and to prevent chromosome rearrangements. Here, we summarize the significant progress made in characterizing the MRX/N complex and its various activities in chromosome metabolism.
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Affiliation(s)
- Julyun Oh
- Biological Sciences Program, Columbia University, New York, NY 10027, USA.
- Department of Microbiology & Immunology, Columbia University Irving Medical Center, New York, NY 10032, USA.
| | - Lorraine S Symington
- Department of Microbiology & Immunology, Columbia University Irving Medical Center, New York, NY 10032, USA.
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12
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Paquin KL, Howlett NG. Understanding the Histone DNA Repair Code: H4K20me2 Makes Its Mark. Mol Cancer Res 2018; 16:1335-1345. [PMID: 29858375 DOI: 10.1158/1541-7786.mcr-17-0688] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2018] [Revised: 03/28/2018] [Accepted: 05/22/2018] [Indexed: 12/11/2022]
Abstract
Chromatin is a highly compact structure that must be rapidly rearranged in order for DNA repair proteins to access sites of damage and facilitate timely and efficient repair. Chromatin plasticity is achieved through multiple processes, including the posttranslational modification of histone tails. In recent years, the impact of histone posttranslational modification on the DNA damage response has become increasingly well recognized, and chromatin plasticity has been firmly linked to efficient DNA repair. One particularly important histone posttranslational modification process is methylation. Here, we focus on the regulation and function of H4K20 methylation (H4K20me) in the DNA damage response and describe the writers, erasers, and readers of this important chromatin mark as well as the combinatorial histone posttranslational modifications that modulate H4K20me recognition. Finally, we discuss the central role of H4K20me in determining if DNA double-strand breaks (DSB) are repaired by the error-prone, nonhomologous DNA end joining pathway or the error-free, homologous recombination pathway. This review article discusses the regulation and function of H4K20me2 in DNA DSB repair and outlines the components and modifications that modulate this important chromatin mark and its fundamental impact on DSB repair pathway choice. Mol Cancer Res; 16(9); 1335-45. ©2018 AACR.
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Affiliation(s)
- Karissa L Paquin
- Department of Cell and Molecular Biology, University of Rhode Island, Kingston, Rhode Island
| | - Niall G Howlett
- Department of Cell and Molecular Biology, University of Rhode Island, Kingston, Rhode Island.
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13
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Mimitou EP, Yamada S, Keeney S. A global view of meiotic double-strand break end resection. Science 2017; 355:40-45. [PMID: 28059759 DOI: 10.1126/science.aak9704] [Citation(s) in RCA: 119] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2016] [Accepted: 11/23/2016] [Indexed: 12/13/2022]
Abstract
DNA double-strand breaks that initiate meiotic recombination are exonucleolytically processed. This 5'→3' resection is a central, conserved feature of recombination but remains poorly understood. To address this lack, we mapped resection endpoints genome-wide at high resolution in Saccharomyces cerevisiae Full-length resection requires Exo1 exonuclease and the DSB-responsive kinase Tel1, but not Sgs1 helicase. Tel1 also promotes efficient and timely resection initiation. Resection endpoints display pronounced heterogeneity between genomic loci that reflects a tendency for nucleosomes to block Exo1, yet Exo1 also appears to digest chromatin with high processivity and at rates similar to naked DNA in vitro. This paradox points to nucleosome destabilization or eviction as a defining feature of the meiotic resection landscape.
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Affiliation(s)
- Eleni P Mimitou
- Molecular Biology Program, Memorial Sloan Kettering Cancer Center, New York, NY 10065, USA
| | - Shintaro Yamada
- Molecular Biology Program, Memorial Sloan Kettering Cancer Center, New York, NY 10065, USA
| | - Scott Keeney
- Molecular Biology Program, Memorial Sloan Kettering Cancer Center, New York, NY 10065, USA. .,Howard Hughes Medical Institute, Memorial Sloan Kettering Cancer Center, New York, NY 10065, USA
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14
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Chen CC, Avdievich E, Zhang Y, Zhang Y, Wei K, Lee K, Edelmann W, Jasin M, LaRocque JR. EXO1 suppresses double-strand break induced homologous recombination between diverged sequences in mammalian cells. DNA Repair (Amst) 2017; 57:98-106. [PMID: 28711786 DOI: 10.1016/j.dnarep.2017.07.003] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2016] [Revised: 07/05/2017] [Accepted: 07/07/2017] [Indexed: 11/17/2022]
Abstract
DNA double-strand breaks (DSBs) can be repaired through several mechanisms, including homologous recombination (HR). While HR between identical sequences is robust in mammalian cells, HR between diverged sequences is suppressed by DNA mismatch-repair (MMR) components such as MSH2. Exonuclease I (EXO1) interacts with the MMR machinery and has been proposed to act downstream of the mismatch recognition proteins in mismatch correction. EXO1 has also been shown to participate in extensive DSB end resection, an initial step in the HR pathway. To assess the contribution of EXO1 to HR in mammalian cells, DSB-inducible reporters were introduced into Exo1-/- mouse embryonic stem cells, including a novel GFP reporter containing several silent polymorphisms to monitor HR between diverged sequences. Compared to HR between identical sequences which was not clearly affected, HR between diverged sequences was substantially increased in Exo1-/- cells although to a lesser extent than seen in Msh2-/- cells. Thus, like canonical MMR proteins, EXO1 can restrain aberrant HR events between diverged sequence elements in the genome.
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Affiliation(s)
- Chun-Chin Chen
- Developmental Biology Program, Memorial Sloan-Kettering Cancer Center, 1275 York Ave., New York, NY, 10065, USA; Weill Cornell Graduate School of Medical Sciences, New York, NY, 10065, USA
| | - Elena Avdievich
- Department of Cell Biology, Albert Einstein College of Medicine, 1300 Morris Park Ave., Bronx, New York, 10461, USA
| | - Yongwei Zhang
- Department of Cell Biology, Albert Einstein College of Medicine, 1300 Morris Park Ave., Bronx, New York, 10461, USA
| | - Yu Zhang
- Developmental Biology Program, Memorial Sloan-Kettering Cancer Center, 1275 York Ave., New York, NY, 10065, USA
| | - Kaichun Wei
- Department of Cell Biology, Albert Einstein College of Medicine, 1300 Morris Park Ave., Bronx, New York, 10461, USA
| | - Kyeryoung Lee
- Department of Cell Biology, Albert Einstein College of Medicine, 1300 Morris Park Ave., Bronx, New York, 10461, USA
| | - Winfried Edelmann
- Department of Cell Biology, Albert Einstein College of Medicine, 1300 Morris Park Ave., Bronx, New York, 10461, USA.
| | - Maria Jasin
- Developmental Biology Program, Memorial Sloan-Kettering Cancer Center, 1275 York Ave., New York, NY, 10065, USA.
| | - Jeannine R LaRocque
- Developmental Biology Program, Memorial Sloan-Kettering Cancer Center, 1275 York Ave., New York, NY, 10065, USA; Department of Human Science, Georgetown University Medical Center, 3700 Reservoir Rd. NW, Washington, D.C., 20057, USA.
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15
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The mismatch repair and meiotic recombination endonuclease Mlh1-Mlh3 is activated by polymer formation and can cleave DNA substrates in trans. PLoS Biol 2017; 15:e2001164. [PMID: 28453523 PMCID: PMC5409509 DOI: 10.1371/journal.pbio.2001164] [Citation(s) in RCA: 53] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2016] [Accepted: 03/31/2017] [Indexed: 01/21/2023] Open
Abstract
Crossing over between homologs is initiated in meiotic prophase by the formation of DNA double-strand breaks that occur throughout the genome. In the major interference-responsive crossover pathway in baker’s yeast, these breaks are resected to form 3' single-strand tails that participate in a homology search, ultimately forming double Holliday junctions (dHJs) that primarily include both homologs. These dHJs are resolved by endonuclease activity to form exclusively crossovers, which are critical for proper homolog segregation in Meiosis I. Recent genetic, biochemical, and molecular studies in yeast are consistent with the hypothesis of Mlh1-Mlh3 DNA mismatch repair complex acting as the major endonuclease activity that resolves dHJs into crossovers. However, the mechanism by which the Mlh1-Mlh3 endonuclease is activated is unknown. Here, we provide evidence that Mlh1-Mlh3 does not behave like a structure-specific endonuclease but forms polymers required to generate nicks in DNA. This conclusion is supported by DNA binding studies performed with different-sized substrates that contain or lack polymerization barriers and endonuclease assays performed with varying ratios of endonuclease-deficient and endonuclease-proficient Mlh1-Mlh3. In addition, Mlh1-Mlh3 can generate religatable double-strand breaks and form an active nucleoprotein complex that can nick DNA substrates in trans. Together these observations argue that Mlh1-Mlh3 may not act like a canonical, RuvC-like Holliday junction resolvase and support a novel model in which Mlh1-Mlh3 is loaded onto DNA to form an activated polymer that cleaves DNA. In sexually reproducing organisms, crossing over between homologous chromosomes in meiosis creates physical linkages required to segregate chromosomes into haploid gametes. In baker’s yeast, which utilizes meiotic recombination pathways conserved in mice and humans, the majority of meiotic crossovers are initiated through the formation of a branched DNA intermediate, which is stabilized by the Msh4-Msh5 complex. This DNA intermediate is further processed to form a structure (a double Holliday junction), which requires the endonuclease activity of the Mlh1-Mlh3 DNA mismatch repair factor to be resolved exclusively into a crossover product. Current meiotic recombination models invoke the use of structure-specific enzymes that symmetrically cleave single Holliday junctions. In this study, we provide evidence that the yeast Mlh1-Mlh3 complex is unlikely to act as a structure-specific enzyme. Furthermore, we showed that Mlh1-Mlh3’s endonuclease activity is dependent upon its ability to form a polymer on DNA and suggest that it is capable of cleaving DNA that is captured in an active complex. Together, our biochemical observations support a novel model involving regulated polymerization of Mlh1-Mlh3 for its cleavage function, potentially in meiotic crossovers or in mismatch repair.
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16
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Lorenz A. Modulation of meiotic homologous recombination by DNA helicases. Yeast 2017; 34:195-203. [PMID: 27930825 DOI: 10.1002/yea.3227] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2016] [Revised: 11/28/2016] [Accepted: 11/28/2016] [Indexed: 12/20/2022] Open
Abstract
DNA helicases are ATP-driven motor proteins which translocate along DNA capable of dismantling DNA-DNA interactions and/or removing proteins bound to DNA. These biochemical capabilities make DNA helicases main regulators of crucial DNA metabolic processes, including DNA replication, DNA repair, and genetic recombination. This budding topic will focus on reviewing the function of DNA helicases important for homologous recombination during meiosis, and discuss recent advances in how these modulators of meiotic recombination are themselves regulated. The emphasis is placed on work in the two model yeasts, Saccharomyces cerevisiae and Schizosaccharomyces pombe, which has vastly expanded our understanding of meiotic homologous recombination, a process whose correct execution is instrumental for healthy gamete formation, and thus functioning sexual reproduction. Copyright © 2016 John Wiley & Sons, Ltd.
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Affiliation(s)
- Alexander Lorenz
- Institute of Medical Sciences, School of Medicine, Medical Sciences and Nutrition, University of Aberdeen, Foresterhill, Aberdeen, AB25 2ZD, UK
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17
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Keijzers G, Liu D, Rasmussen LJ. Exonuclease 1 and its versatile roles in DNA repair. Crit Rev Biochem Mol Biol 2016; 51:440-451. [PMID: 27494243 DOI: 10.1080/10409238.2016.1215407] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
Exonuclease 1 (EXO1) is a multifunctional 5' → 3' exonuclease and a DNA structure-specific DNA endonuclease. EXO1 plays roles in DNA replication, DNA mismatch repair (MMR) and DNA double-stranded break repair (DSBR) in lower and higher eukaryotes and contributes to meiosis, immunoglobulin maturation, and micro-mediated end-joining in higher eukaryotes. In human cells, EXO1 is also thought to play a role in telomere maintenance. Mutations in the human EXO1 gene correlate with increased susceptibility to some cancers. This review summarizes recent studies on the enzymatic functions and biological roles of EXO1, its possible protective role against cancer and aging, and regulation of EXO1 by posttranslational modification.
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Affiliation(s)
- Guido Keijzers
- a Department of Cellular and Molecular Medicine , Center for Healthy Aging, University of Copenhagen , Copenhagen , Denmark
| | - Dekang Liu
- a Department of Cellular and Molecular Medicine , Center for Healthy Aging, University of Copenhagen , Copenhagen , Denmark
| | - Lene Juel Rasmussen
- a Department of Cellular and Molecular Medicine , Center for Healthy Aging, University of Copenhagen , Copenhagen , Denmark
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18
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Manhart CM, Alani E. Roles for mismatch repair family proteins in promoting meiotic crossing over. DNA Repair (Amst) 2016; 38:84-93. [PMID: 26686657 PMCID: PMC4740264 DOI: 10.1016/j.dnarep.2015.11.024] [Citation(s) in RCA: 75] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2015] [Revised: 08/14/2015] [Accepted: 11/30/2015] [Indexed: 12/13/2022]
Abstract
The mismatch repair (MMR) family complexes Msh4-Msh5 and Mlh1-Mlh3 act with Exo1 and Sgs1-Top3-Rmi1 in a meiotic double strand break repair pathway that results in the asymmetric cleavage of double Holliday junctions (dHJ) to form crossovers. This review discusses how meiotic roles for Msh4-Msh5 and Mlh1-Mlh3 do not fit paradigms established for post-replicative MMR. We also outline models used to explain how these factors promote the formation of meiotic crossovers required for the accurate segregation of chromosome homologs during the Meiosis I division.
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Affiliation(s)
- Carol M Manhart
- Department of Molecular Biology and Genetics, Cornell University, 457 Biotechnology Building, Ithaca, NY 14853-2703, USA
| | - Eric Alani
- Department of Molecular Biology and Genetics, Cornell University, 457 Biotechnology Building, Ithaca, NY 14853-2703, USA.
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19
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A Computational Approach to Estimating Nondisjunction Frequency in Saccharomyces cerevisiae. G3-GENES GENOMES GENETICS 2016; 6:669-82. [PMID: 26747203 PMCID: PMC4777129 DOI: 10.1534/g3.115.024380] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Errors segregating homologous chromosomes during meiosis result in aneuploid gametes and are the largest contributing factor to birth defects and spontaneous abortions in humans. Saccharomyces cerevisiae has long served as a model organism for studying the gene network supporting normal chromosome segregation. Measuring homolog nondisjunction frequencies is laborious, and involves dissecting thousands of tetrads to detect missegregation of individually marked chromosomes. Here we describe a computational method (TetFit) to estimate the relative contributions of meiosis I nondisjunction and random-spore death to spore inviability in wild type and mutant strains. These values are based on finding the best-fit distribution of 4, 3, 2, 1, and 0 viable-spore tetrads to an observed distribution. Using TetFit, we found that meiosis I nondisjunction is an intrinsic component of spore inviability in wild-type strains. We show proof-of-principle that the calculated average meiosis I nondisjunction frequency determined by TetFit closely matches empirically determined values in mutant strains. Using these published data sets, TetFit uncovered two classes of mutants: Class A mutants skew toward increased nondisjunction death, and include those with known defects in establishing pairing, recombination, and/or synapsis of homologous chromosomes. Class B mutants skew toward random spore death, and include those with defects in sister-chromatid cohesion and centromere function. Epistasis analysis using TetFit is facilitated by the low numbers of tetrads (as few as 200) required to compare the contributions to spore death in different mutant backgrounds. TetFit analysis does not require any special strain construction, and can be applied to previously observed tetrad distributions.
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20
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Abstract
The study of homologous recombination has its historical roots in meiosis. In this context, recombination occurs as a programmed event that culminates in the formation of crossovers, which are essential for accurate chromosome segregation and create new combinations of parental alleles. Thus, meiotic recombination underlies both the independent assortment of parental chromosomes and genetic linkage. This review highlights the features of meiotic recombination that distinguish it from recombinational repair in somatic cells, and how the molecular processes of meiotic recombination are embedded and interdependent with the chromosome structures that characterize meiotic prophase. A more in-depth review presents our understanding of how crossover and noncrossover pathways of meiotic recombination are differentiated and regulated. The final section of this review summarizes the studies that have defined defective recombination as a leading cause of pregnancy loss and congenital disease in humans.
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Affiliation(s)
- Neil Hunter
- Howard Hughes Medical Institute, Department of Microbiology & Molecular Genetics, Department of Molecular & Cellular Biology, Department of Cell Biology & Human Anatomy, University of California Davis, Davis, California 95616
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21
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Lukaszewicz A, Shodhan A, Loidl J. Exo1 and Mre11 execute meiotic DSB end resection in the protist Tetrahymena. DNA Repair (Amst) 2015; 35:137-43. [PMID: 26519827 DOI: 10.1016/j.dnarep.2015.08.005] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2015] [Revised: 08/26/2015] [Accepted: 08/26/2015] [Indexed: 01/09/2023]
Abstract
The resection of 5'-DNA ends at a double-strand break (DSB) is an essential step in recombinational repair, as it exposes 3' single-stranded DNA (ssDNA) tails for interaction with a repair template. In mitosis, Exo1 and Sgs1 have a conserved function in the formation of long ssDNA tails, whereas this step in the processing of programmed meiotic DSBs is less well-characterized across model organisms. In budding yeast, which has been most intensely studied in this respect, Exo1 is a major meiotic nuclease. In addition, it exerts a nuclease-independent function later in meiosis in the conversion of DNA joint molecules into ZMM-dependent crossovers. In order to gain insight into the diverse meiotic roles of Exo1, we investigated the effect of Exo1 deletion in the ciliated protist Tetrahymena. We found that Exo1 together with Mre11, but without the help of Sgs1, promotes meiotic DSB end resection. Resection is completely eliminated only if both Mre11 and Exo1 are missing. This is consistent with the yeast model where Mre11 promotes resection in the 3'-5' direction and Exo1 in the opposite 5'-3' direction. However, while the endonuclease activity of Mre11 is essential to create an entry site for exonucleases and hence to start resection in budding yeast, Tetrahymena Exo1 is able to create single-stranded DNA in the absence of Mre11. Excluding a possible contribution of the Mre11 cofactor Sae2 (Com1) as an autonomous endonuclease, we conclude that there exists another unknown nuclease that initiates DSB processing in Tetrahymena. Consistent with the absence of the ZMM crossover pathway in Tetrahymena, crossover formation is independent of Exo1.
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Affiliation(s)
- Agnieszka Lukaszewicz
- Department of Chromosome Biology, University of Vienna, Vienna Biocenter (VBC), Dr. Bohr-Gasse 9, A-1030 Vienna, Austria
| | - Anura Shodhan
- Department of Chromosome Biology, University of Vienna, Vienna Biocenter (VBC), Dr. Bohr-Gasse 9, A-1030 Vienna, Austria
| | - Josef Loidl
- Department of Chromosome Biology, University of Vienna, Vienna Biocenter (VBC), Dr. Bohr-Gasse 9, A-1030 Vienna, Austria.
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22
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Abstract
RecA/Rad51 catalyzed pairing of homologous DNA strands, initiated by polymerization of the recombinase on single-stranded DNA (ssDNA), is a universal feature of homologous recombination (HR). Generation of ssDNA from a double-strand break (DSB) requires nucleolytic degradation of the 5'-terminated strands to generate 3'-ssDNA tails, a process referred to as 5'-3' end resection. The RecBCD helicase-nuclease complex is the main end-processing machine in Gram-negative bacteria. Mre11-Rad50 and Mre11-Rad50-Xrs2/Nbs1 can play a direct role in end resection in archaea and eukaryota, respectively, by removing end-blocking lesions and act indirectly by recruiting the helicases and nucleases responsible for extensive resection. In eukaryotic cells, the initiation of end resection has emerged as a critical regulatory step to differentiate between homology-dependent and end-joining repair of DSBs.
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The role of Exo1p exonuclease in DNA end resection to generate gene conversion tracts in Saccharomyces cerevisiae. Genetics 2014; 197:1097-109. [PMID: 24835424 PMCID: PMC4125386 DOI: 10.1534/genetics.114.164517] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
The yeast Exo1p nuclease functions in multiple cellular roles: resection of DNA ends generated during recombination, telomere stability, DNA mismatch repair, and expansion of gaps formed during the repair of UV-induced DNA damage. In this study, we performed high-resolution mapping of spontaneous and UV-induced recombination events between homologs in exo1 strains, comparing the results with spontaneous and UV-induced recombination events in wild-type strains. One important comparison was the lengths of gene conversion tracts. Gene conversion events are usually interpreted as reflecting heteroduplex formation between interacting DNA molecules, followed by repair of mismatches within the heteroduplex. In most models of recombination, the length of the gene conversion tract is a function of the length of single-stranded DNA generated by end resection. Since the Exo1p has an important role in end resection, a reduction in the lengths of gene conversion tracts in exo1 strains was expected. In accordance with this expectation, gene conversion tract lengths associated with spontaneous crossovers in exo1 strains were reduced about twofold relative to wild type. For UV-induced events, conversion tract lengths associated with crossovers were also shorter for the exo1 strain than for the wild-type strain (3.2 and 7.6 kb, respectively). Unexpectedly, however, the lengths of conversion tracts that were unassociated with crossovers were longer in the exo1 strain than in the wild-type strain (6.2 and 4.8 kb, respectively). Alternative models of recombination in which the lengths of conversion tracts are determined by break-induced replication or oversynthesis during strand invasion are proposed to account for these observations.
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Gray S, Allison RM, Garcia V, Goldman ASH, Neale MJ. Positive regulation of meiotic DNA double-strand break formation by activation of the DNA damage checkpoint kinase Mec1(ATR). Open Biol 2013; 3:130019. [PMID: 23902647 PMCID: PMC3728922 DOI: 10.1098/rsob.130019] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
During meiosis, formation and repair of programmed DNA double-strand breaks (DSBs) create genetic exchange between homologous chromosomes-a process that is critical for reductional meiotic chromosome segregation and the production of genetically diverse sexually reproducing populations. Meiotic DSB formation is a complex process, requiring numerous proteins, of which Spo11 is the evolutionarily conserved catalytic subunit. Precisely how Spo11 and its accessory proteins function or are regulated is unclear. Here, we use Saccharomyces cerevisiae to reveal that meiotic DSB formation is modulated by the Mec1(ATR) branch of the DNA damage signalling cascade, promoting DSB formation when Spo11-mediated catalysis is compromised. Activation of the positive feedback pathway correlates with the formation of single-stranded DNA (ssDNA) recombination intermediates and activation of the downstream kinase, Mek1. We show that the requirement for checkpoint activation can be rescued by prolonging meiotic prophase by deleting the NDT80 transcription factor, and that even transient prophase arrest caused by Ndt80 depletion is sufficient to restore meiotic spore viability in checkpoint mutants. Our observations are unexpected given recent reports that the complementary kinase pathway Tel1(ATM) acts to inhibit DSB formation. We propose that such antagonistic regulation of DSB formation by Mec1 and Tel1 creates a regulatory mechanism, where the absolute frequency of DSBs is maintained at a level optimal for genetic exchange and efficient chromosome segregation.
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Affiliation(s)
- Stephen Gray
- MRC Genome Damage and Stability Centre, School of Life Sciences, University of Sussex, Brighton BN1 9RQ, UK
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25
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Mammalian Exo1 encodes both structural and catalytic functions that play distinct roles in essential biological processes. Proc Natl Acad Sci U S A 2013; 110:E2470-9. [PMID: 23754438 DOI: 10.1073/pnas.1308512110] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Mammalian Exonuclease 1 (EXO1) is an evolutionarily conserved, multifunctional exonuclease involved in DNA damage repair, replication, immunoglobulin diversity, meiosis, and telomere maintenance. It has been assumed that EXO1 participates in these processes primarily through its exonuclease activity, but recent studies also suggest that EXO1 has a structural function in the assembly of higher-order protein complexes. To dissect the enzymatic and nonenzymatic roles of EXO1 in the different biological processes in vivo, we generated an EXO1-E109K knockin (Exo1(EK)) mouse expressing a stable exonuclease-deficient protein and, for comparison, a fully EXO1-deficient (Exo1(null)) mouse. In contrast to Exo1(null/null) mice, Exo1(EK/EK) mice retained mismatch repair activity and displayed normal class switch recombination and meiosis. However, both Exo1-mutant lines showed defects in DNA damage response including DNA double-strand break repair (DSBR) through DNA end resection, chromosomal stability, and tumor suppression, indicating that the enzymatic function is required for those processes. On a transformation-related protein 53 (Trp53)-null background, the DSBR defect caused by the E109K mutation altered the tumor spectrum but did not affect the overall survival as compared with p53-Exo1(null) mice, whose defects in both DSBR and mismatch repair also compromised survival. The separation of these functions demonstrates the differential requirement for the structural function and nuclease activity of mammalian EXO1 in distinct DNA repair processes and tumorigenesis in vivo.
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26
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Zakharyevich K, Tang S, Ma Y, Hunter N. Delineation of joint molecule resolution pathways in meiosis identifies a crossover-specific resolvase. Cell 2012; 149:334-47. [PMID: 22500800 DOI: 10.1016/j.cell.2012.03.023] [Citation(s) in RCA: 212] [Impact Index Per Article: 17.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2011] [Revised: 01/31/2012] [Accepted: 03/27/2012] [Indexed: 11/18/2022]
Abstract
At the final step of homologous recombination, Holliday junction-containing joint molecules (JMs) are resolved to form crossover or noncrossover products. The enzymes responsible for JM resolution in vivo remain uncertain, but three distinct endonucleases capable of resolving JMs in vitro have been identified: Mus81-Mms4(EME1), Slx1-Slx4(BTBD12), and Yen1(GEN1). Using physical monitoring of recombination during budding yeast meiosis, we show that all three endonucleases are capable of promoting JM resolution in vivo. However, in mms4 slx4 yen1 triple mutants, JM resolution and crossing over occur efficiently. Paradoxically, crossing over in this background is strongly dependent on the Blooms helicase ortholog Sgs1, a component of a well-characterized anticrossover activity. Sgs1-dependent crossing over, but not JM resolution per se, also requires XPG family nuclease Exo1 and the MutLγ complex Mlh1-Mlh3. Thus, Sgs1, Exo1, and MutLγ together define a previously undescribed meiotic JM resolution pathway that produces the majority of crossovers in budding yeast and, by inference, in mammals.
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Affiliation(s)
- Kseniya Zakharyevich
- Department of Microbiology, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA
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27
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Abstract
Repair of meiotic double-strand breaks (DSBs) uses the homolog and recombination to yield crossovers while alternative pathways such as nonhomologous end joining (NHEJ) are suppressed. Our results indicate that NHEJ is blocked at two steps of DSB repair during meiotic prophase: first by the activity of the MCM-like protein MEI-218, which is required for crossover formation, and, second, by Rad51-related proteins SPN-B (XRCC3) and SPN-D (RAD51C), which physically interact and promote homologous recombination (HR). We further show that the MCM-like proteins also promote the activity of the DSB repair checkpoint pathway, indicating an early requirement for these proteins in DSB processing. We propose that when a meiotic DSB is formed in the absence of both MEI-218 and SPN-B or SPN-D, a DSB substrate is generated that can enter the NHEJ repair pathway. Indeed, due to its high error rate, multiple barriers may have evolved to prevent NHEJ activity during meiosis.
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28
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Garcia V, Phelps SEL, Gray S, Neale MJ. Bidirectional resection of DNA double-strand breaks by Mre11 and Exo1. Nature 2011; 479:241-4. [PMID: 22002605 PMCID: PMC3214165 DOI: 10.1038/nature10515] [Citation(s) in RCA: 325] [Impact Index Per Article: 25.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2011] [Accepted: 08/30/2011] [Indexed: 01/22/2023]
Abstract
Repair of DNA double-strand breaks (DSBs) by homologous recombination requires resection of 5'-termini to generate 3'-single-strand DNA tails. Key components of this reaction are exonuclease 1 and the bifunctional endo/exonuclease, Mre11 (refs 2-4). Mre11 endonuclease activity is critical when DSB termini are blocked by bound protein--such as by the DNA end-joining complex, topoisomerases or the meiotic transesterase Spo11 (refs 7-13)--but a specific function for the Mre11 3'-5' exonuclease activity has remained elusive. Here we use Saccharomyces cerevisiae to reveal a role for the Mre11 exonuclease during the resection of Spo11-linked 5'-DNA termini in vivo. We show that the residual resection observed in Exo1-mutant cells is dependent on Mre11, and that both exonuclease activities are required for efficient DSB repair. Previous work has indicated that resection traverses unidirectionally. Using a combination of physical assays for 5'-end processing, our results indicate an alternative mechanism involving bidirectional resection. First, Mre11 nicks the strand to be resected up to 300 nucleotides from the 5'-terminus of the DSB--much further away than previously assumed. Second, this nick enables resection in a bidirectional manner, using Exo1 in the 5'-3' direction away from the DSB, and Mre11 in the 3'-5' direction towards the DSB end. Mre11 exonuclease activity also confers resistance to DNA damage in cycling cells, suggesting that Mre11-catalysed resection may be a general feature of various DNA repair pathways.
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Affiliation(s)
- Valerie Garcia
- Genome Damage and Stability Centre, The University of Sussex, Brighton, BN1 9RQ, UK
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29
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Abstract
DNA double-strand breaks (DSBs) are cytotoxic lesions that can result in mutagenic events or cell death if left unrepaired or repaired inappropriately. Cells use two major pathways for DSB repair: nonhomologous end joining (NHEJ) and homologous recombination (HR). The choice between these pathways depends on the phase of the cell cycle and the nature of the DSB ends. A critical determinant of repair pathway choice is the initiation of 5'-3' resection of DNA ends, which commits cells to homology-dependent repair, and prevents repair by classical NHEJ. Here, we review the components of the end resection machinery, the role of end structure, and the cell-cycle phase on resection and the interplay of end processing with NHEJ.
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Affiliation(s)
- Lorraine S Symington
- Department of Microbiology & Immunology, Columbia University Medical Center, New York, New York 10032, USA.
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30
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Ceballos SJ, Heyer WD. Functions of the Snf2/Swi2 family Rad54 motor protein in homologous recombination. BIOCHIMICA ET BIOPHYSICA ACTA 2011; 1809:509-23. [PMID: 21704205 PMCID: PMC3171615 DOI: 10.1016/j.bbagrm.2011.06.006] [Citation(s) in RCA: 101] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/26/2011] [Revised: 05/27/2011] [Accepted: 06/06/2011] [Indexed: 11/25/2022]
Abstract
Homologous recombination is a central pathway to maintain genomic stability and is involved in the repair of DNA damage and replication fork support, as well as accurate chromosome segregation during meiosis. Rad54 is a dsDNA-dependent ATPase of the Snf2/Swi2 family of SF2 helicases, although Rad54 lacks classical helicase activity and cannot carry out the strand displacement reactions typical for DNA helicases. Rad54 is a potent and processive motor protein that translocates on dsDNA, potentially executing several functions in recombinational DNA repair. Rad54 acts in concert with Rad51, the central protein of recombination that performs the key reactions of homology search and DNA strand invasion. Here, we will review the role of the Rad54 protein in homologous recombination with an emphasis on mechanistic studies with the yeast and human enzymes. We will discuss how these results relate to in vivo functions of Rad54 during homologous recombination in somatic cells and during meiosis. This article is part of a Special Issue entitled: Snf2/Swi2 ATPase structure and function.
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Affiliation(s)
- Shannon J. Ceballos
- Department of Microbiology, University of California, Davis, Davis, CA 95616-8665
| | - Wolf-Dietrich Heyer
- Department of Microbiology, University of California, Davis, Davis, CA 95616-8665
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA 95616-8665
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31
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Cell cycle regulation of DNA double-strand break end resection by Cdk1-dependent Dna2 phosphorylation. Nat Struct Mol Biol 2011; 18:1015-9. [PMID: 21841787 PMCID: PMC3168961 DOI: 10.1038/nsmb.2105] [Citation(s) in RCA: 141] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2010] [Accepted: 06/13/2011] [Indexed: 12/23/2022]
Abstract
DNA recombination pathways are regulated by the cell cycle to coordinate with replication. Cyclin-dependent kinase (Cdk1) promotes efficient 5' strand resection at DNA double-strand breaks (DSBs), the initial step of homologous recombination and damage checkpoint activation. The Mre11-Rad50-Xrs2 complex with Sae2 initiates resection, whereas two nucleases, Exo1 and Dna2, and the DNA helicase-topoisomerase complex Sgs1-Top3-Rmi1 generate longer ssDNA at DSBs. Using Saccharomyces cerevisiae, we provide evidence for Cdk1-dependent phosphorylation of the resection nuclease Dna2 at Thr4, Ser17 and Ser237 that stimulates its recruitment to DSBs, resection and subsequent Mec1-dependent phosphorylation. Poorly recruited dna2T4A S17A S237A and dna2ΔN248 mutant proteins promote resection only in the presence of Exo1, suggesting cross-talk between Dna2- and Exo1-dependent resection pathways.
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32
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Mimitou EP, Symington LS. DNA end resection--unraveling the tail. DNA Repair (Amst) 2011; 10:344-8. [PMID: 21227759 DOI: 10.1016/j.dnarep.2010.12.004] [Citation(s) in RCA: 156] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2010] [Revised: 12/01/2010] [Accepted: 12/13/2010] [Indexed: 12/25/2022]
Abstract
Homology-dependent repair of DNA double-strand breaks (DSBs) initiates by the 5'-3' resection of the DNA ends to create single-stranded DNA (ssDNA), the substrate for Rad51/RecA binding. Long tracts of ssDNA are also required for activation of the ATR-mediated checkpoint response. Thus, identifying the proteins required and the underlying mechanism for DNA end resection has been an intense area of investigation. Genetic studies in Saccharomyces cerevisiae show that end resection takes place in two steps. Initially, a short oligonucleotide tract is removed from the 5' strand to create an early intermediate with a short 3' overhang. Then in a second step the early intermediate is rapidly processed generating an extensive tract of ssDNA. The first step is dependent on the highly conserved Mre11-Rad50-Xrs2 complex and Sae2, while the second step employs the exonuclease Exo1 and/or the helicase-topoisomerase complex Sgs1-Top3-Rmi1 with the endonuclease Dna2. Here we review recent in vitro and in vivo findings that shed more light into the mechanisms of DSB processing in mitotic and meiotic DSB repair as well as in telomere metabolism.
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Affiliation(s)
- Eleni P Mimitou
- Department of Microbiology and Immunology, Columbia University Medical Center, 701 W. 168th St., New York, NY 10032, USA
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33
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Zakharyevich K, Ma Y, Tang S, Hwang PYH, Boiteux S, Hunter N. Temporally and biochemically distinct activities of Exo1 during meiosis: double-strand break resection and resolution of double Holliday junctions. Mol Cell 2010; 40:1001-15. [PMID: 21172664 PMCID: PMC3061447 DOI: 10.1016/j.molcel.2010.11.032] [Citation(s) in RCA: 178] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2010] [Revised: 09/21/2010] [Accepted: 10/21/2010] [Indexed: 01/09/2023]
Abstract
The Rad2/XPG family nuclease, Exo1, functions in a variety of DNA repair pathways. During meiosis, Exo1 promotes crossover recombination and thereby facilitates chromosome segregation at the first division. Meiotic recombination is initiated by programmed DNA double-strand breaks (DSBs). Nucleolytic resection of DSBs generates long 3' single-strand tails that undergo strand exchange with a homologous chromosome to form joint molecule (JM) intermediates. We show that meiotic DSB resection is dramatically reduced in exo1Δ mutants and test the idea that Exo1-catalyzed resection promotes crossing over by facilitating formation of crossover-specific JMs called double Holliday junctions (dHJs). Contrary to this idea, dHJs form at wild-type levels in exo1Δ mutants, implying that Exo1 has a second function that promotes resolution of dHJs into crossovers. Surprisingly, the dHJ resolution function of Exo1 is independent of its nuclease activities but requires interaction with the putative endonuclease complex, Mlh1-Mlh3. Thus, the DSB resection and procrossover functions of Exo1 during meiosis involve temporally and biochemically distinct activities.
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Affiliation(s)
- Kseniya Zakharyevich
- Howard Hughes Medical Institute and the Departments of Microbiology, Molecular & Cellular Biology and Cell Biology & Human Anatomy, University of California Davis, One Shields Ave., Davis, CA 95616, USA
| | - Yunmei Ma
- Howard Hughes Medical Institute and the Departments of Microbiology, Molecular & Cellular Biology and Cell Biology & Human Anatomy, University of California Davis, One Shields Ave., Davis, CA 95616, USA
| | - Shangming Tang
- Howard Hughes Medical Institute and the Departments of Microbiology, Molecular & Cellular Biology and Cell Biology & Human Anatomy, University of California Davis, One Shields Ave., Davis, CA 95616, USA
| | - Patty Yi-Hwa Hwang
- Howard Hughes Medical Institute and the Departments of Microbiology, Molecular & Cellular Biology and Cell Biology & Human Anatomy, University of California Davis, One Shields Ave., Davis, CA 95616, USA
| | - Serge Boiteux
- CEA SDV/IRCM UMR217 CNRS Radiobiologie Moléculaire et Cellulaire, CEA Fontenay aux Roses, France
| | - Neil Hunter
- Howard Hughes Medical Institute and the Departments of Microbiology, Molecular & Cellular Biology and Cell Biology & Human Anatomy, University of California Davis, One Shields Ave., Davis, CA 95616, USA
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34
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Hodgson A, Terentyev Y, Johnson RA, Bishop-Bailey A, Angevin T, Croucher A, Goldman ASH. Mre11 and Exo1 contribute to the initiation and processivity of resection at meiotic double-strand breaks made independently of Spo11. DNA Repair (Amst) 2010; 10:138-48. [PMID: 21146476 DOI: 10.1016/j.dnarep.2010.11.008] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2010] [Revised: 10/29/2010] [Accepted: 11/18/2010] [Indexed: 11/18/2022]
Abstract
During meiosis DNA double-strand breaks (DSBs) are induced and repaired by homologous recombination to create gene conversion and crossover products. Mostly these DSBs are made by Spo11, which covalently binds to the DSB ends. More rarely in Saccharomyces cerevisiae, other meiotic DSBs are formed by self-homing endonucleases such as VDE, which is site specific and does not covalently bind to the DSB ends. We have used experimentally located VDE-DSB sites to analyse an intermediate step in homologous recombination, resection of the single-strand ending 5' at the DSB site. Analysis of strains with different mutant alleles of MRE11 (mre11-58S and mre11-H125N) and deleted for EXO1 indicated that these two nucleases make significant contributions to repair of VDE-DSBs. Physical analysis of single-stranded repair intermediates indicates that efficient initiation and processivity of resection at VDE-DSBs require both Mre11 and Exo1, with loss of function for either protein causing severe delay in resection. We propose that these experiments model what happens at Spo11-DSBs after removal of the covalently bound protein, and that Mre11 and Exo1 are the major nucleases involved in creating resection tracts of widely varying lengths typical of meiotic recombination.
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Affiliation(s)
- Adam Hodgson
- Department of Molecular Biology & Biotechnology, Krebs Institute, The University of Sheffield, Sheffield, UK
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