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Qiu Y, Kang YM, Korfmann C, Pouyet F, Eckford A, Palazzo AF. The GC-content at the 5' ends of human protein-coding genes is undergoing mutational decay. Genome Biol 2024; 25:219. [PMID: 39138526 PMCID: PMC11323403 DOI: 10.1186/s13059-024-03364-x] [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: 05/28/2024] [Accepted: 07/31/2024] [Indexed: 08/15/2024] Open
Abstract
BACKGROUND In vertebrates, most protein-coding genes have a peak of GC-content near their 5' transcriptional start site (TSS). This feature promotes both the efficient nuclear export and translation of mRNAs. Despite the importance of GC-content for RNA metabolism, its general features, origin, and maintenance remain mysterious. We investigate the evolutionary forces shaping GC-content at the transcriptional start site (TSS) of genes through both comparative genomic analysis of nucleotide substitution rates between different species and by examining human de novo mutations. RESULTS Our data suggests that GC-peaks at TSSs were present in the last common ancestor of amniotes, and likely that of vertebrates. We observe that in apes and rodents, where recombination is directed away from TSSs by PRDM9, GC-content at the 5' end of protein-coding gene is currently undergoing mutational decay. In canids, which lack PRDM9 and perform recombination at TSSs, GC-content at the 5' end of protein-coding is increasing. We show that these patterns extend into the 5' end of the open reading frame, thus impacting synonymous codon position choices. CONCLUSIONS Our results indicate that the dynamics of this GC-peak in amniotes is largely shaped by historic patterns of recombination. Since decay of GC-content towards the mutation rate equilibrium is the default state for non-functional DNA, the observed decrease in GC-content at TSSs in apes and rodents indicates that the GC-peak is not being maintained by selection on most protein-coding genes in those species.
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Affiliation(s)
- Yi Qiu
- Department of Biochemistry, University of Toronto, Toronto, Ontario, M5G1M1, Canada
| | - Yoon Mo Kang
- Department of Biochemistry, University of Toronto, Toronto, Ontario, M5G1M1, Canada
| | - Christopher Korfmann
- Department of Electrical Engineering and Computer Science, York University, Toronto, Ontario, M3J1P3, Canada
| | - Fanny Pouyet
- Laboratoire Interdisciplinaire des Sciences du Numérique, Université Paris-Saclay, 91190, Gif-sur-Yvette, France
| | - Andrew Eckford
- Department of Electrical Engineering and Computer Science, York University, Toronto, Ontario, M3J1P3, Canada
| | - Alexander F Palazzo
- Department of Biochemistry, University of Toronto, Toronto, Ontario, M5G1M1, Canada.
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2
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Mathis N, Allam A, Kissling L, Marquart KF, Schmidheini L, Solari C, Balázs Z, Krauthammer M, Schwank G. Predicting prime editing efficiency and product purity by deep learning. Nat Biotechnol 2023; 41:1151-1159. [PMID: 36646933 PMCID: PMC7614945 DOI: 10.1038/s41587-022-01613-7] [Citation(s) in RCA: 40] [Impact Index Per Article: 40.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2022] [Accepted: 11/15/2022] [Indexed: 01/18/2023]
Abstract
Prime editing is a versatile genome editing tool but requires experimental optimization of the prime editing guide RNA (pegRNA) to achieve high editing efficiency. Here we conducted a high-throughput screen to analyze prime editing outcomes of 92,423 pegRNAs on a highly diverse set of 13,349 human pathogenic mutations that include base substitutions, insertions and deletions. Based on this dataset, we identified sequence context features that influence prime editing and trained PRIDICT (prime editing guide prediction), an attention-based bidirectional recurrent neural network. PRIDICT reliably predicts editing rates for all small-sized genetic changes with a Spearman's R of 0.85 and 0.78 for intended and unintended edits, respectively. We validated PRIDICT on endogenous editing sites as well as an external dataset and showed that pegRNAs with high (>70) versus low (<70) PRIDICT scores showed substantially increased prime editing efficiencies in different cell types in vitro (12-fold) and in hepatocytes in vivo (tenfold), highlighting the value of PRIDICT for basic and for translational research applications.
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Affiliation(s)
- Nicolas Mathis
- Institute of Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland
| | - Ahmed Allam
- Department of Quantitative Biomedicine, University of Zurich, Zurich, Switzerland
| | - Lucas Kissling
- Institute of Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland
| | - Kim Fabiano Marquart
- Institute of Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland
- Institute of Molecular Health Sciences, ETH Zurich, Zurich, Switzerland
| | - Lukas Schmidheini
- Institute of Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland
- Institute of Molecular Health Sciences, ETH Zurich, Zurich, Switzerland
| | - Cristina Solari
- Institute of Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland
| | - Zsolt Balázs
- Department of Quantitative Biomedicine, University of Zurich, Zurich, Switzerland
| | - Michael Krauthammer
- Department of Quantitative Biomedicine, University of Zurich, Zurich, Switzerland.
| | - Gerald Schwank
- Institute of Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland.
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3
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Satange R, Chang CC, Li L, Lin SH, Neidle S, Hou MH. Synergistic binding of actinomycin D and echinomycin to DNA mismatch sites and their combined anti-tumour effects. Nucleic Acids Res 2023; 51:3540-3555. [PMID: 36919604 PMCID: PMC10164580 DOI: 10.1093/nar/gkad156] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2023] [Revised: 02/07/2023] [Accepted: 02/23/2023] [Indexed: 03/16/2023] Open
Abstract
Combination cancer chemotherapy is one of the most useful treatment methods to achieve a synergistic effect and reduce the toxicity of dosing with a single drug. Here, we use a combination of two well-established anticancer DNA intercalators, actinomycin D (ActD) and echinomycin (Echi), to screen their binding capabilities with DNA duplexes containing different mismatches embedded within Watson-Crick base-pairs. We have found that combining ActD and Echi preferentially stabilised thymine-related T:T mismatches. The enhanced stability of the DNA duplex-drug complexes is mainly due to the cooperative binding of the two drugs to the mismatch duplex, with many stacking interactions between the two different drug molecules. Since the repair of thymine-related mismatches is less efficient in mismatch repair (MMR)-deficient cancer cells, we have also demonstrated that the combination of ActD and Echi exhibits enhanced synergistic effects against MMR-deficient HCT116 cells and synergy is maintained in a MMR-related MLH1 gene knockdown in SW620 cells. We further accessed the clinical potential of the two-drug combination approach with a xenograft mouse model of a colorectal MMR-deficient cancer, which has resulted in a significant synergistic anti-tumour effect. The current study provides a novel approach for the development of combination chemotherapy for the treatment of cancers related to DNA-mismatches.
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Affiliation(s)
- Roshan Satange
- Institute of Genomics and Bioinformatics, National Chung Hsing University, Taichung402, Taiwan
- Ph.D. Program in Medical Biotechnology, National Chung Hsing University, Taichung402, Taiwan
| | - Chih-Chun Chang
- Graduate Institute of Biotechnology, National Chung Hsing University, Taichung402, Taiwan
| | - Long‐Yuan Li
- Department of Life Sciences, National Chung Hsing University, Taichung402, Taiwan
| | - Sheng-Hao Lin
- Institute of Genomics and Bioinformatics, National Chung Hsing University, Taichung402, Taiwan
- Division of Chest Medicine, Changhua Christian Hospital, Changhua City, Taiwan
- Departement of Post-Baccalaureate Medicine, College of Medicine, National Chung Hsing University, Taichung402, Taiwan
| | - Stephen Neidle
- The School of Pharmacy, University College London, London, WC1N 1AX, UK
| | - Ming-Hon Hou
- Institute of Genomics and Bioinformatics, National Chung Hsing University, Taichung402, Taiwan
- Ph.D. Program in Medical Biotechnology, National Chung Hsing University, Taichung402, Taiwan
- Graduate Institute of Biotechnology, National Chung Hsing University, Taichung402, Taiwan
- Department of Life Sciences, National Chung Hsing University, Taichung402, Taiwan
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4
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Pokusaeva VO, Diez AR, Espinar L, Pérez AT, Filion GJ. Strand asymmetry influences mismatch resolution during a single-strand annealing. Genome Biol 2022; 23:93. [PMID: 35414014 PMCID: PMC9001825 DOI: 10.1186/s13059-022-02665-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2019] [Accepted: 03/30/2022] [Indexed: 02/08/2023] Open
Abstract
Background Biases of DNA repair can shape the nucleotide landscape of genomes at evolutionary timescales. The molecular mechanisms of those biases are still poorly understood because it is difficult to isolate the contributions of DNA repair from those of DNA damage. Results Here, we develop a genome-wide assay whereby the same DNA lesion is repaired in different genomic contexts. We insert thousands of barcoded transposons carrying a reporter of DNA mismatch repair in the genome of mouse embryonic stem cells. Upon inducing a double-strand break between tandem repeats, a mismatch is generated if the break is repaired through single-strand annealing. The resolution of the mismatch showed a 60–80% bias in favor of the strand with the longest 3′ flap. The location of the lesion in the genome and the type of mismatch had little influence on the bias. Instead, we observe a complete reversal of the bias when the longest 3′ flap is moved to the opposite strand by changing the position of the double-strand break in the reporter. Conclusions These results suggest that the processing of the double-strand break has a major influence on the repair of mismatches during a single-strand annealing. Supplementary Information The online version contains supplementary material available at 10.1186/s13059-022-02665-3.
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Affiliation(s)
- Victoria O Pokusaeva
- Center for Genomic Regulation (CRG), The Barcelona Institute of Science and Technology, Dr. Aiguader 88, 08003, Barcelona, Spain.,Present Address: Institute of Science and Technology Austria, Am Campus 1, Klosterneuburg, Austria
| | - Aránzazu Rosado Diez
- Center for Genomic Regulation (CRG), The Barcelona Institute of Science and Technology, Dr. Aiguader 88, 08003, Barcelona, Spain.,Present Address: H12O-CNIO Lung Cancer Clinical Research Unit, i + 12 Research Institute, Spanish National Cancer Research Center (CNIO), Madrid, Spain
| | - Lorena Espinar
- Center for Genomic Regulation (CRG), The Barcelona Institute of Science and Technology, Dr. Aiguader 88, 08003, Barcelona, Spain
| | - Albert Torelló Pérez
- Center for Genomic Regulation (CRG), The Barcelona Institute of Science and Technology, Dr. Aiguader 88, 08003, Barcelona, Spain
| | - Guillaume J Filion
- Center for Genomic Regulation (CRG), The Barcelona Institute of Science and Technology, Dr. Aiguader 88, 08003, Barcelona, Spain. .,University Pompeu Fabra (UPF), Barcelona, Spain. .,Present Address: Department Biological Sciences, University of Toronto Scarborough, Toronto, Canada.
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5
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Zhang M, Yang D, Gold B. Origins of nonsense mutations in human tumor suppressor genes. Mutat Res 2021; 823:111761. [PMID: 34461460 DOI: 10.1016/j.mrfmmm.2021.111761] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2019] [Revised: 07/27/2020] [Accepted: 08/12/2021] [Indexed: 11/26/2022]
Abstract
Understanding the origins of mutations in tumor suppressor genes and oncogenes associated with cancers in different tissues is critical to the development of potential prevention strategies. Analysis of >10,000 nonsense mutations in 63 tumor suppressor genes based on the ratio of the number of nonsense mutations per codon type is reported for each gene. The ratio for C•G→T•A nonsense mutations at Arg CGA codons to the number of CGA codons in all cancers is 23 (3088 total nonsense mutations for 134 CGA codons in the 63 suppressor genes). The ratio for this codon, which is attributed to hydrolytic deamination of 5-methylcytosine at CpG sites based on the sequence context, is 6-fold higher than the next highest ratio that involves a C•G→T•A transition at Trp TGG codons. C•G→A•T transversions at Glu, Ser, Tyr, Gly and Cys codons account for 25 % of the total nonsense mutations but the mutation per codon ratio for these codons is 1.0. Analysis of the bases 5' of the mutated CGA codons in the 63 tumor suppressor genes in all cancers shows a preference of 5'-G > C ∼ T ∼ A, which is not indicative of a role for enzymatic deamination by deaminases. Overall C•G→T•A mutations account for 61 % of all of the nonsense mutations in the collection of tumor suppressor genes. It is demonstrated that the ratio of C•G→T•A deamination-associated nonsense mutations at CGA codons (hydrolytic deamination) to the number of frame shift insertion/deletion mutations (i.e., replication based) for 5 major tumor suppressors genes are very similar in 3 different tissues that undergo a wide range of stem cell divisions. Therefore, the frequency of deamination mutations parallels the number of stem cell replications. This may reflect the generation of more solvent accessible single-stranded DNA regions during polymerization that are kinetically more prone to deamination.
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Affiliation(s)
- Min Zhang
- Department of Pharmaceutical Sciences, University of Pittsburgh, Salk Hall, Pittsburgh, PA, 15261, United States
| | - Da Yang
- Department of Pharmaceutical Sciences, University of Pittsburgh, Salk Hall, Pittsburgh, PA, 15261, United States
| | - Barry Gold
- Department of Pharmaceutical Sciences, University of Pittsburgh, Salk Hall, Pittsburgh, PA, 15261, United States.
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6
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Bergman J, Schierup MH. Population dynamics of GC-changing mutations in humans and great apes. Genetics 2021; 218:6291657. [PMID: 34081117 DOI: 10.1093/genetics/iyab083] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2021] [Accepted: 05/27/2021] [Indexed: 11/14/2022] Open
Abstract
The nucleotide composition of the genome is a balance between origin and fixation rates of different mutations. For example, it is well-known that transitions occur more frequently than transversions, particularly at CpG sites. Differences in fixation rates of mutation types are less explored. Specifically, recombination-associated GC-biased gene conversion (gBGC) may differentially impact GC-changing mutations, due to differences in their genomic distributions and efficiency of mismatch repair mechanisms. Given that recombination evolves rapidly across species, we explore gBGC of different mutation types across human populations and great ape species. We report a stronger correlation between segregating GC frequency and recombination for transitions than for transversions. Notably, CpG transitions are most strongly affected by gBGC in humans and chimpanzees. We show that the overall strength of gBGC is generally correlated with effective population sizes in humans, with some notable exceptions, such as a stronger effect of gBGC on non-CpG transitions in populations of European descent. Furthermore, species of the Gorilla and Pongo genus have a greatly reduced gBGC effect on CpG sites. We also study the dependence of gBGC dynamics on flanking nucleotides and show that some mutation types evolve in opposition to the gBGC expectation, likely due to hypermutability of specific nucleotide contexts. Our results highlight the importance of different gBGC dynamics experienced by GC-changing mutations and their impact on nucleotide composition evolution.
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Affiliation(s)
- Juraj Bergman
- Bioinformatics Research Institute, Aarhus University, DK-8000 Aarhus C, Denmark
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7
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Cytosine Methylation Affects the Mutability of Neighboring Nucleotides in Germline and Soma. Genetics 2020; 214:809-823. [PMID: 32079595 DOI: 10.1534/genetics.120.303028] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2019] [Accepted: 02/12/2020] [Indexed: 02/07/2023] Open
Abstract
Methylated cytosines deaminate at higher rates than unmethylated cytosines, and the lesions they produce are repaired less efficiently. As a result, methylated cytosines are mutational hotspots. Here, combining rare polymorphism and base-resolution methylation data in humans, Arabidopsis thaliana, and rice (Oryza sativa), we present evidence that methylation state affects mutation dynamics not only at the focal cytosine but also at neighboring nucleotides. In humans, contrary to prior suggestions, we find that nucleotides in the close vicinity (±3 bp) of methylated cytosines mutate less frequently. Reduced mutability around methylated CpGs is also observed in cancer genomes, considering single nucleotide variants alongside tissue-of-origin-matched methylation data. In contrast, methylation is associated with increased neighborhood mutation risk in A. thaliana and rice. The difference in neighborhood mutation risk is less pronounced further away from the focal CpG and modulated by regional GC content. Our results are consistent with a model where altered risk at neighboring bases is linked to lesion formation at the focal CpG and subsequent long-patch repair. Our findings indicate that cytosine methylation has a broader mutational footprint than is commonly assumed.
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8
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Jabbari K, Wirtz J, Rauscher M, Wiehe T. A common genomic code for chromatin architecture and recombination landscape. PLoS One 2019; 14:e0213278. [PMID: 30865674 PMCID: PMC6415826 DOI: 10.1371/journal.pone.0213278] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2018] [Accepted: 02/18/2019] [Indexed: 12/14/2022] Open
Abstract
Recent findings established a link between DNA sequence composition and interphase chromatin architecture and explained the evolutionary conservation of TADs (Topologically Associated Domains) and LADs (Lamina Associated Domains) in mammals. This prompted us to analyse conformation capture and recombination rate data to study the relationship between chromatin architecture and recombination landscape of human and mouse genomes. The results reveal that: (1) low recombination domains and blocks of elevated linkage disequilibrium tend to coincide with TADs and isochores, indicating co-evolving regulatory elements and genes in insulated neighbourhoods; (2) double strand break (DSB) and recombination frequencies increase in the short loops of GC-rich TADs, whereas recombination cold spots are typical of LADs and (3) the binding and loading of proteins, which are critical for DSB and meiotic recombination (SPO11, DMC1, H3K4me3 and PRMD9) are higher in GC-rich TADs. One explanation for these observations is that the occurrence of DSB and recombination in meiotic cells are associated with compositional and epigenetic features (genomic code) that influence DNA stiffness/flexibility and appear to be similar to those guiding the chromatin architecture in the interphase nucleus of pre-leptotene cells.
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Affiliation(s)
- Kamel Jabbari
- Institute for Genetics, Biocenter Cologne, University of Cologne, Köln, Germany
- * E-mail:
| | - Johannes Wirtz
- Institute for Genetics, Biocenter Cologne, University of Cologne, Köln, Germany
| | - Martina Rauscher
- Institute for Genetics, Biocenter Cologne, University of Cologne, Köln, Germany
| | - Thomas Wiehe
- Institute for Genetics, Biocenter Cologne, University of Cologne, Köln, Germany
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9
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Chen Y, Huang C, Bai C, Du C, Liao J, Dong Q. In vivo DNA mismatch repair measurement in zebrafish embryos and its use in screening of environmental carcinogens. JOURNAL OF HAZARDOUS MATERIALS 2016; 302:296-303. [PMID: 26476317 DOI: 10.1016/j.jhazmat.2015.09.056] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/01/2015] [Revised: 09/24/2015] [Accepted: 09/26/2015] [Indexed: 06/05/2023]
Abstract
Impairment of DNA mismatch repair (MMR) function leads to the development and progression of certain cancers. Many environmental contaminants can target DNA MMR system. Currently, measurement of MMR activity is limited to in vitro or in vivo methods at the cell line level, and reports on measurement of MMR activity at the live organism level are lacking. Here, we report an efficient method to measure DNA MMR activity in zebrafish embryos. A G-T mismatch was introduced into enhanced green fluorescent protein (EGFP) gene. Repair of the G-T mismatch to G-C in the heteroduplex plasmid generates a functional EGFP expression. The heteroduplex plasmid and a similarly constructed homoduplex plasmid were injected in parallel into the same batch of embryos at 1-cell stage and EGFP expression in EGFP positive embryos was quantified at 24 h after injection. MMR efficiency was calculated as the total fluorescence intensity of embryos injected with the heteroduplex construct divided by that of embryos injected with the homoduplex construct. Our results showed 73% reduction of MMR activity in embryos derived from MMR-deficient mlh1 mutant fish (positive control) when compared with embryos from MMR-competent wild type AB line fish, indicating feasibility of in vivo MMR activity measurement in zebrafish embryos. We further applied this novel assay for measurement of MMR efficiency in embryos exposed to environmental chemicals such as cadmium chloride (CdCl2), benzo[a]pyrene (BaP), and perfluorooctanesulphonic acid (PFOS) from 6 hpf to 24 hpf. We observed significant reductions of MMR efficiency in embryos exposed to 0.1 μM CdCl2 (52%) and 0.5 μM BaP (34%), but no effect in embryos exposed to PFOS. Our study for the first time provides a model system for in vivo measurement of DNA MMR activity at the organism level, which has important implications in risk assessment of various environmental carcinogens.
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Affiliation(s)
- Yuanhong Chen
- Institute of Environmental Safety and Human Health, Wenzhou Medical University, Wenzhou 325035, PR China
| | - Changjiang Huang
- Institute of Environmental Safety and Human Health, Wenzhou Medical University, Wenzhou 325035, PR China.
| | - Chenglian Bai
- Institute of Environmental Safety and Human Health, Wenzhou Medical University, Wenzhou 325035, PR China
| | - Changchun Du
- Institute of Environmental Safety and Human Health, Wenzhou Medical University, Wenzhou 325035, PR China
| | - Junhua Liao
- Institute of Environmental Safety and Human Health, Wenzhou Medical University, Wenzhou 325035, PR China
| | - Qiaoxiang Dong
- Institute of Environmental Safety and Human Health, Wenzhou Medical University, Wenzhou 325035, PR China; School of Laboratory Medicine and Life Science, Wenzhou Medical University, Wenzhou 325035, PR China.
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10
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Robinson MC, Stone EA, Singh ND. Population genomic analysis reveals no evidence for GC-biased gene conversion in Drosophila melanogaster. Mol Biol Evol 2013; 31:425-33. [PMID: 24214536 DOI: 10.1093/molbev/mst220] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Gene conversion is the nonreciprocal exchange of genetic material between homologous chromosomes. Multiple lines of evidence from a variety of taxa strongly suggest that gene conversion events are biased toward GC-bearing alleles. However, in Drosophila, the data have largely been indirect and unclear, with some studies supporting the predictions of a GC-biased gene conversion model and other data showing contradictory findings. Here, we test whether gene conversion events are GC-biased in Drosophila melanogaster using whole-genome polymorphism and divergence data. Our results provide no support for GC-biased gene conversion and thus suggest that this process is unlikely to significantly contribute to patterns of polymorphism and divergence in this system.
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Affiliation(s)
- Matthew C Robinson
- Department of Biological Sciences, Program in Genetics, North Carolina State University
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11
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Clément Y, Arndt PF. Meiotic recombination strongly influences GC-content evolution in short regions in the mouse genome. Mol Biol Evol 2013; 30:2612-8. [PMID: 24030552 DOI: 10.1093/molbev/mst154] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Meiotic recombination is known to influence GC-content evolution in large regions of mammalian genomes by favoring the fixation of G and C alleles and increasing the rate of A/T to G/C substitutions. This process is known as GC-biased gene conversion (gBGC). Until recently, genome-wide measures of fine-scale recombination activity were unavailable in mice. Additionally, comparative studies focusing on mouse were limited as the closest organism with its genome fully sequenced was rat. Here, we make use of the recent mapping of double strand breaks (DSBs), the first step of meiotic recombination, in the mouse genome and of the sequencing of mouse closely related subspecies to analyze the fine-scale evolutionary signature of meiotic recombination on GC-content evolution in recombination hotspots, short regions that undergo extreme rates of recombination. We measure substitution rates around DSB hotspots and observe that gBGC is affecting a very short region (≈ 1 kbp) in length around these hotspots. Furthermore, we can infer that the locations of hotspots evolved rapidly during mouse evolution.
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Affiliation(s)
- Yves Clément
- Montpellier SupAgro, Unité Mixte de Recherche 1334, Amélioration Génétique et Adaptation des Plantes Méditerranéennes et Tropicales, Montpellier, France
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12
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Leushkin EV, Bazykin GA. Short indels are subject to insertion-biased gene conversion. Evolution 2013; 67:2604-13. [PMID: 24033170 DOI: 10.1111/evo.12129] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2013] [Accepted: 04/05/2013] [Indexed: 11/29/2022]
Abstract
Recombination between homologous loci is accompanied by formation of heteroduplexes. Repairing mismatches in heteroduplexes often leads to single nucleotide substitutions in a process known as gene conversion. Gene conversion was shown to be GC-biased in different organisms; that is, a W(A or T)→S(G or C) substitution is more likely in this process than a S→W substitution. Here, we show that the insertion/deletion ratio for short noncoding indels that reach fixation between species is positively correlated with the recombination rate in Drosophila melanogaster, Homo sapiens, and Saccharomyces cerevisiae. This correlation is both due to an increase of the fixation rate of insertions and decrease of the fixation rate of deletions in regions of high recombination. Whole-genome data on indel polymorphism and divergence in D. melanogaster rule out mutation biases and selection as the cause of this trend, pointing to insertion-biased gene conversion as the most likely explanation. The bias toward insertions is the strongest for single-nucleotide indels, and decreases with indel length. In regions of high recombination rate this bias leads to an up to ∼5-fold excess of fixed short insertions over deletions, and substantially affects the evolution of DNA segments.
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Affiliation(s)
- Evgeny V Leushkin
- Department of Bioengineering and Bioinformatics, Lomonosov Moscow State University, Leninskye Gory 1-73, Moscow, 119992, Russia; Institute for Information Transmission Problems of the Russian Academy of Sciences (Kharkevich Institute), Bolshoi Karetny pereulok, 19, Moscow, 127994, Russia.
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13
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Roesti M, Moser D, Berner D. Recombination in the threespine stickleback genome-patterns and consequences. Mol Ecol 2013; 22:3014-27. [DOI: 10.1111/mec.12322] [Citation(s) in RCA: 179] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2013] [Revised: 03/08/2013] [Accepted: 03/17/2013] [Indexed: 12/23/2022]
Affiliation(s)
- Marius Roesti
- Zoological Institute; University of Basel; Vesalgasse 1 CH-4051 Basel Switzerland
| | - Dario Moser
- Zoological Institute; University of Basel; Vesalgasse 1 CH-4051 Basel Switzerland
| | - Daniel Berner
- Zoological Institute; University of Basel; Vesalgasse 1 CH-4051 Basel Switzerland
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14
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Lesecque Y, Mouchiroud D, Duret L. GC-biased gene conversion in yeast is specifically associated with crossovers: molecular mechanisms and evolutionary significance. Mol Biol Evol 2013; 30:1409-19. [PMID: 23505044 PMCID: PMC3649680 DOI: 10.1093/molbev/mst056] [Citation(s) in RCA: 79] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
GC-biased gene conversion (gBGC) is a process associated with recombination that favors the transmission of GC alleles over AT alleles during meiosis. gBGC plays a major role in genome evolution in many eukaryotes. However, the molecular mechanisms of gBGC are still unknown. Different steps of the recombination process could potentially cause gBGC: the formation of double-strand breaks (DSBs), the invasion of the homologous or sister chromatid, and the repair of mismatches in heteroduplexes. To investigate these models, we analyzed a genome-wide data set of crossovers (COs) and noncrossovers (NCOs) in Saccharomyces cerevisiae. We demonstrate that the overtransmission of GC alleles is specific to COs and that it occurs among conversion tracts in which all alleles are converted from the same donor haplotype. Thus, gBGC results from a process that leads to long-patch repair. We show that gBGC is associated with longer tracts and that it is driven by the nature (GC or AT) of the alleles located at the extremities of the tract. These observations invalidate the hypotheses that gBGC is due to the base excision repair machinery or to a bias in DSB formation and suggest that in S. cerevisiae, gBGC is caused by the mismatch repair (MMR) system. We propose that the presence of nicks on both DNA strands during CO resolution could be the cause of the bias in MMR activity. Our observations are consistent with the hypothesis that gBGC is a nonadaptive consequence of a selective pressure to limit the mutation rate in mitotic cells.
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Affiliation(s)
- Yann Lesecque
- Laboratoire de Biométrie et Biologie Evolutive, UMR CNRS 5558, Université de Lyon, Université Lyon 1, Villeurbanne, France
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15
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Popa A, Samollow P, Gautier C, Mouchiroud D. The sex-specific impact of meiotic recombination on nucleotide composition. Genome Biol Evol 2012; 4:412-22. [PMID: 22417915 PMCID: PMC3318449 DOI: 10.1093/gbe/evs023] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Meiotic recombination is an important evolutionary force shaping the nucleotide landscape of genomes. For most vertebrates, the frequency of recombination varies slightly or considerably between the sexes (heterochiasmy). In humans, male, rather than female, recombination rate has been found to be more highly correlated with the guanine and cytosine (GC) content across the genome. In the present study, we review the results in human and extend the examination of the evolutionary impact of heterochiasmy beyond primates to include four additional eutherian mammals (mouse, dog, pig, and sheep), a metatherian mammal (opossum), and a bird (chicken). Specifically, we compared sex-specific recombination rates (RRs) with nucleotide substitution patterns evaluated in transposable elements. Our results, based on a comparative approach, reveal a great diversity in the relationship between heterochiasmy and nucleotide composition. We find that the stronger male impact on this relationship is a conserved feature of human, mouse, dog, and sheep. In contrast, variation in genomic GC content in pig and opossum is more strongly correlated with female, rather than male, RR. Moreover, we show that the sex-differential impact of recombination is mainly driven by the chromosomal localization of recombination events. Independent of sex, the higher the RR in a genomic region and the longer this recombination activity is conserved in time, the stronger the bias in nucleotide substitution pattern, through such mechanisms as biased gene conversion. Over time, this bias will increase the local GC content of the region.
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Ananda G, Chiaromonte F, Makova KD. A genome-wide view of mutation rate co-variation using multivariate analyses. Genome Biol 2011; 12:R27. [PMID: 21426544 PMCID: PMC3129677 DOI: 10.1186/gb-2011-12-3-r27] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2010] [Revised: 02/21/2011] [Accepted: 03/22/2011] [Indexed: 01/03/2023] Open
Abstract
Background While the abundance of available sequenced genomes has led to many studies of regional heterogeneity in mutation rates, the co-variation among rates of different mutation types remains largely unexplored, hindering a deeper understanding of mutagenesis and genome dynamics. Here, utilizing primate and rodent genomic alignments, we apply two multivariate analysis techniques (principal components and canonical correlations) to investigate the structure of rate co-variation for four mutation types and simultaneously explore the associations with multiple genomic features at different genomic scales and phylogenetic distances. Results We observe a consistent, largely linear co-variation among rates of nucleotide substitutions, small insertions and small deletions, with some non-linear associations detected among these rates on chromosome X and near autosomal telomeres. This co-variation appears to be shaped by a common set of genomic features, some previously investigated and some novel to this study (nuclear lamina binding sites, methylated non-CpG sites and nucleosome-free regions). Strong non-linear relationships are also detected among genomic features near the centromeres of large chromosomes. Microsatellite mutability co-varies with other mutation rates at finer scales, but not at 1 Mb, and shows varying degrees of association with genomic features at different scales. Conclusions Our results allow us to speculate about the role of different molecular mechanisms, such as replication, recombination, repair and local chromatin environment, in mutagenesis. The software tools developed for our analyses are available through Galaxy, an open-source genomics portal, to facilitate the use of multivariate techniques in future large-scale genomics studies.
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Affiliation(s)
- Guruprasad Ananda
- Center for Medical Genomics, Penn State University, University Park, PA 16802, USA
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17
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Clément Y, Arndt PF. Substitution patterns are under different influences in primates and rodents. Genome Biol Evol 2011; 3:236-45. [PMID: 21339508 PMCID: PMC3068003 DOI: 10.1093/gbe/evr011] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
There are large-scale variations of the GC-content along mammalian chromosomes that have been called isochore structures. Primates and rodents have different isochore structures, which suggests that these lineages exhibit different modes of GC-content evolution. It has been shown that, in the human lineage, GC-biased gene conversion (gBGC), a neutral process associated with meiotic recombination, acts on GC-content evolution by influencing A or T to G or C substitution rates. We computed genome-wide substitution patterns in the mouse lineage from multiple alignments and compared them with substitution patterns in the human lineage. We found that in the mouse lineage, gBGC is active but weaker than in the human lineage and that male-specific recombination better predicts GC-content evolution than female-specific recombination. Furthermore, we were able to show that G or C to A or T substitution rates are predicted by a combination of different factors in both lineages. A or T to G or C substitution rates are most strongly predicted by meiotic recombination in the human lineage but by CpG odds ratio (the observed CpG frequency normalized by the expected CpG frequency) in the mouse lineage, suggesting that substitution patterns are under different influences in primates and rodents.
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Affiliation(s)
- Yves Clément
- Department of Computational Molecular Biology, Max Planck Institute for Molecular Genetics, Berlin, Germany.
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18
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Mechanisms of recombination between diverged sequences in wild-type and BLM-deficient mouse and human cells. Mol Cell Biol 2010; 30:1887-97. [PMID: 20154148 DOI: 10.1128/mcb.01553-09] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Double-strand breaks (DSBs) are particularly deleterious DNA lesions for which cells have developed multiple mechanisms of repair. One major mechanism of DSB repair in mammalian cells is homologous recombination (HR), whereby a homologous donor sequence is used as a template for repair. For this reason, HR repair of DSBs is also being exploited for gene modification in possible therapeutic approaches. HR is sensitive to sequence divergence, such that the cell has developed ways to suppress recombination between diverged ("homeologous") sequences. In this report, we have examined several aspects of HR between homeologous sequences in mouse and human cells. We found that gene conversion tracts are similar for mouse and human cells and are generally < or =100 bp, even in Msh2(-)(/)(-) cells which fail to suppress homeologous recombination. Gene conversion tracts are mostly unidirectional, with no observed mutations. Additionally, no alterations were observed in the donor sequences. While both mouse and human cells suppress homeologous recombination, the suppression is substantially less in the transformed human cells, despite similarities in the gene conversion tracts. BLM-deficient mouse and human cells suppress homeologous recombination to a similar extent as wild-type cells, unlike Sgs1-deficient Saccharomyces cerevisiae.
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Identifying concerted evolution and gene conversion in mammalian gene pairs lasting over 100 million years. BMC Evol Biol 2009; 9:156. [PMID: 19583854 PMCID: PMC2720389 DOI: 10.1186/1471-2148-9-156] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2009] [Accepted: 07/07/2009] [Indexed: 01/17/2023] Open
Abstract
BACKGROUND Concerted evolution occurs in multigene families and is characterized by stretches of homogeneity and higher sequence similarity between paralogues than between orthologues. Here we identify human gene pairs that have undergone concerted evolution, caused by ongoing gene conversion, since at least the human-mouse divergence. Our strategy involved the identification of duplicated genes with greater similarity within a species than between species. These genes were required to be present in multiple mammalian genomes, suggesting duplication early in mammalian divergence. To eliminate genes that have been conserved due to strong purifying selection, our analysis also required at least one intron to have retained high sequence similarity between paralogues. RESULTS We identified three human gene pairs undergoing concerted evolution (BMP8A/B, DDX19A/B, and TUBG1/2). Phylogenetic investigations reveal that in each case the duplication appears to have occurred prior to eutherian mammalian radiation, with exactly two paralogues present in all examined species. This indicates that all three gene duplication events were established over 100 million years ago. CONCLUSION The extended duration of concerted evolution in multiple distant lineages suggests that there has been prolonged homogenization of specific segments within these gene pairs. Although we speculate that selection for homogenization could have been utilized in order to maintain crucial homo- or hetero- binding domains, it remains unclear why gene conversion has persisted for such extended periods of time. Through these analyses, our results demonstrate additional examples of a process that plays a definite, although unspecified, role in molecular evolution.
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20
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The correlation between recombination rate and dinucleotide bias in Drosophila melanogaster. J Mol Evol 2008; 67:358-67. [PMID: 18797953 DOI: 10.1007/s00239-008-9150-0] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2008] [Revised: 06/12/2008] [Accepted: 06/23/2008] [Indexed: 10/21/2022]
Abstract
Revealing how recombination affects genomic sequence is of great significance to our understanding of genome evolution. The present paper focuses on the correlation between recombination rate and dinucleotide bias in Drosophila melanogaster genome. Our results show that the overall dinucleotide bias is positively correlated with recombination rate for genomic sequences including untranslated regions, introns, intergenic regions, and coding sequences. The correlation patterns of individual dinucleotide biases with recombination rate are presented. Possible mechanisms of interaction between recombination and dinucleotide bias are discussed. Our data indicate that there may be a genome-wide universal mechanism acting between recombination rate and dinucleotide bias, which is likely to be neighbor-dependent biased gene conversion.
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21
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Stoklosa T, Poplawski T, Koptyra M, Nieborowska-Skorska M, Basak G, Slupianek A, Rayevskaya M, Seferynska I, Herrera L, Blasiak J, Skorski T. BCR/ABL inhibits mismatch repair to protect from apoptosis and induce point mutations. Cancer Res 2008; 68:2576-80. [PMID: 18413724 DOI: 10.1158/0008-5472.can-07-6858] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BCR/ABL kinase-positive chronic myelogenous leukemia (CML) cells display genomic instability leading to point mutations in various genes including bcr/abl and p53, eventually causing resistance to imatinib and malignant progression of the disease. Mismatch repair (MMR) is responsible for detecting misincorporated nucleotides, resulting in excision repair before point mutations occur and/or induction of apoptosis to avoid propagation of cells carrying excessive DNA lesions. To assess MMR activity in CML, we used an in vivo assay using the plasmid substrate containing enhanced green fluorescent protein (EGFP) gene corrupted by T:G mismatch in the start codon; therefore, MMR restores EGFP expression. The efficacy of MMR was reduced approximately 2-fold in BCR/ABL-positive cell lines and CD34(+) CML cells compared with normal counterparts. MMR was also challenged by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), which generates O(6)-methylguanine and O(4)-methylthymine recognized by MMR system. Impaired MMR activity in leukemia cells was associated with better survival, accumulation of p53 but not of p73, and lack of activation of caspase 3 after MNNG treatment. In contrast, parental cells displayed accumulation of p53, p73, and activation of caspase 3, resulting in cell death. Ouabain-resistance test detecting mutations in the Na(+)/K(+) ATPase was used to investigate the effect of BCR/ABL kinase-mediated inhibition of MMR on mutagenesis. BCR/ABL-positive cells surviving the treatment with MNNG displayed approximately 15-fold higher mutation frequency than parental counterparts and predominantly G:C-->A:T and A:T-->G:C mutator phenotype typical for MNNG-induced unrepaired lesions. In conclusion, these results suggest that BCR/ABL kinase abrogates MMR activity to inhibit apoptosis and induce mutator phenotype.
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Affiliation(s)
- Tomasz Stoklosa
- Department of Microbiology and Immunology, Temple University, Philadelphia, Pennsylvania 19140, USA
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Duret L, Arndt PF. The impact of recombination on nucleotide substitutions in the human genome. PLoS Genet 2008; 4:e1000071. [PMID: 18464896 PMCID: PMC2346554 DOI: 10.1371/journal.pgen.1000071] [Citation(s) in RCA: 254] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2007] [Accepted: 04/11/2008] [Indexed: 01/19/2023] Open
Abstract
Unraveling the evolutionary forces responsible for variations of neutral substitution patterns among taxa or along genomes is a major issue for detecting selection within sequences. Mammalian genomes show large-scale regional variations of GC-content (the isochores), but the substitution processes at the origin of this structure are poorly understood. We analyzed the pattern of neutral substitutions in 1 Gb of primate non-coding regions. We show that the GC-content toward which sequences are evolving is strongly negatively correlated to the distance to telomeres and positively correlated to the rate of crossovers (R2 = 47%). This demonstrates that recombination has a major impact on substitution patterns in human, driving the evolution of GC-content. The evolution of GC-content correlates much more strongly with male than with female crossover rate, which rules out selectionist models for the evolution of isochores. This effect of recombination is most probably a consequence of the neutral process of biased gene conversion (BGC) occurring within recombination hotspots. We show that the predictions of this model fit very well with the observed substitution patterns in the human genome. This model notably explains the positive correlation between substitution rate and recombination rate. Theoretical calculations indicate that variations in population size or density in recombination hotspots can have a very strong impact on the evolution of base composition. Furthermore, recombination hotspots can create strong substitution hotspots. This molecular drive affects both coding and non-coding regions. We therefore conclude that along with mutation, selection and drift, BGC is one of the major factors driving genome evolution. Our results also shed light on variations in the rate of crossover relative to non-crossover events, along chromosomes and according to sex, and also on the conservation of hotspot density between human and chimp. Mammalian genomes show a very strong heterogeneity of base composition along chromosomes (the so-called isochores). The functional significance of these peculiar genomic landscapes is highly debated: do isochores confer some selective advantage, or are they simply the by-product of neutral evolutionary processes? To resolve this issue, we analyzed the pattern of substitution in the human genome by comparison with chimpanzee and macaque. We show that the evolution of base composition (GC-content) is essentially determined by the rate of recombination. This effect appears to be much stronger in male than in female germline, which rules out selective explanations for the evolution of isochores. We show that this impact of recombination is most probably a consequence of the process of biased gene conversion (BGC). This neutral process mimics the action of selection and can induce strong substitution hotspots within recombination hotspots, sometimes leading to the fixation of deleterious mutations. BGC appears to be one of the major factors driving genome evolution. It is therefore essential to take this process into account if we want to be able to interpret genome sequences.
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Affiliation(s)
- Laurent Duret
- Laboratoire de Biométrie et Biologie Evolutive, Université de Lyon, Université Lyon 1, CNRS, UMR 5558, Villeurbanne, France
- * E-mail: (LD); (PFA)
| | - Peter F. Arndt
- Department for Computational Molecular Biology, Max Planck Institute for Molecular Genetics, Berlin, Germany
- * E-mail: (LD); (PFA)
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23
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Díaz-Castillo C, Golic KG. Evolution of gene sequence in response to chromosomal location. Genetics 2007; 177:359-74. [PMID: 17890366 PMCID: PMC2013720 DOI: 10.1534/genetics.107.077081] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2007] [Accepted: 06/06/2007] [Indexed: 12/26/2022] Open
Abstract
Evolutionary forces acting on the repetitive DNA of heterochromatin are not constrained by the same considerations that apply to protein-coding genes. Consequently, such sequences are subject to rapid evolutionary change. By examining the Troponin C gene family of Drosophila melanogaster, which has euchromatic and heterochromatic members, we find that protein-coding genes also evolve in response to their chromosomal location. The heterochromatic members of the family show a reduced CG content and increased variation in DNA sequence. We show that the CG reduction applies broadly to the protein-coding sequences of genes located at the heterochromatin:euchromatin interface, with a very strong correlation between CG content and the distance from centric heterochromatin. We also observe a similar trend in the transition from telomeric heterochromatin to euchromatin. We propose that the methylation of DNA is one of the forces driving this sequence evolution.
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24
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Galtier N, Duret L. Adaptation or biased gene conversion? Extending the null hypothesis of molecular evolution. Trends Genet 2007; 23:273-7. [PMID: 17418442 DOI: 10.1016/j.tig.2007.03.011] [Citation(s) in RCA: 165] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2006] [Revised: 03/01/2007] [Accepted: 03/21/2007] [Indexed: 11/26/2022]
Abstract
The analysis of evolutionary rates is a popular approach to characterizing the effect of natural selection at the molecular level. Sequences contributing to species adaptation are expected to evolve faster than nonfunctional sequences because favourable mutations have a higher fixation probability than neutral ones. Such an accelerated rate of evolution might be due to factors other than natural selection, in particular GC-biased gene conversion. This is true of neutral sequences, but also of constrained sequences, which can be illustrated using the mouse Fxy gene. Several criteria can discriminate between the natural selection and biased gene conversion models. These criteria suggest that the recently reported human accelerated regions are most likely the result of biased gene conversion. We argue that these regions, far from contributing to human adaptation, might represent the Achilles' heel of our genome.
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Affiliation(s)
- Nicolas Galtier
- CNRS UMR 5554 - Institut des Sciences de l'Evolution, Université Montpellier 2 - CC64, Place E. Bataillon, 34095 Montpellier Cedex, France.
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25
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Buard J, de Massy B. Playing hide and seek with mammalian meiotic crossover hotspots. Trends Genet 2007; 23:301-9. [PMID: 17434233 DOI: 10.1016/j.tig.2007.03.014] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2006] [Revised: 03/14/2007] [Accepted: 03/29/2007] [Indexed: 11/30/2022]
Abstract
Crossovers (COs) are essential for meiosis and contribute to genome diversity by promoting the reassociation of alleles, and thus improve the efficiency of selection. COs are not randomly distributed but are found at specific regions, or CO hotspots. Recent results have revealed the historical recombination rates and the distribution of hotspots across the human genome. Surprisingly, CO hotspots are highly dynamic, as shown by differences in activity between individuals, populations and closely related species. We propose a role for DNA methylation in preventing the formation of COs, a regulation that might explain, in part, the correlation between recombination rates and GC content in mammals.
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Affiliation(s)
- Jérôme Buard
- Institute of Human Genetics, UPR1142-CNRS, 141 rue de la Cardonille, 34396 Montpellier cedex 5, France
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26
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Duret L, Eyre-Walker A, Galtier N. A new perspective on isochore evolution. Gene 2006; 385:71-4. [PMID: 16971063 DOI: 10.1016/j.gene.2006.04.030] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2006] [Accepted: 04/07/2006] [Indexed: 11/30/2022]
Abstract
The genomes of mammals and birds show dramatic variation in base composition over large scales, the so called isochore structure of the genome. The origin of isochores is still controversial: various neutral and selectionist models have been proposed--and criticized--since the discovery of isochores in the 1970s. The availability of complete mammalian genomes has yielded new opportunities for addressing this question. In particular, it was recently proposed that (i) the isochore structure is declining in many mammalian groups, and that (ii) GC-content is influenced by local recombination rate, possibly via the mechanism of GC-biased gene conversion. In this article we review the existing support for these two hypotheses, and discuss how they can be combined to provide a new perspective on isochore evolution.
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Affiliation(s)
- Laurent Duret
- CNRS UMR 5558, BBE, Université C. Bernard Lyon 1, France
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27
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Khelifi A, Meunier J, Duret L, Mouchiroud D. GC content evolution of the human and mouse genomes: insights from the study of processed pseudogenes in regions of different recombination rates. J Mol Evol 2006; 62:745-52. [PMID: 16752212 DOI: 10.1007/s00239-005-0186-0] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2005] [Accepted: 02/02/2006] [Indexed: 01/27/2023]
Abstract
Processed pseudogenes are generated by reverse transcription of a functional gene. They are generally nonfunctional after their insertion and, as a consequence, are no longer subjected to the selective constraints associated with functional genes. Because of this property they can be used as neutral markers in molecular evolution. In this work, we investigated the relationship between the evolution of GC content in recently inserted processed pseudogenes and the local recombination pattern in two mammalian genomes (human and mouse). We confirmed, using original markers, that recombination drives GC content in the human genome and we demonstrated that this is also true for the mouse genome despite lower recombination rates. Finally, we discussed the consequences on isochores evolution and the contrast between the human and the mouse pattern.
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Affiliation(s)
- Adel Khelifi
- Laboratoire de Biométrie et Biologie Evolutive, UMR CNRS 5558, Université Claude Bernard-Lyon 1, 16 rue Raphael Dubois, 69622 Villeurbanne Cedex, France.
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28
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Abstract
5-Methylcytosine in DNA is genetically unstable. Methylated CpG (mCpG) sequences frequently undergo mutation resulting in a general depletion of this dinucleotide sequence in mammalian genomes. In human genetic disease- and cancer-relevant genes, mCpG sequences are mutational hotspots. It is an almost universally accepted dogma that these mutations are caused by random deamination of 5-methylcytosines. However, it is plausible that mCpG transitions are not caused simply by spontaneous deamination of 5-methylcytosine in double-stranded DNA but by other processes including, for example, mCpG-specific base modification by endogenous or exogenous mutagens or, alternatively, by secondary factors operating at mCpG sequences and promoting deamination. We also discuss that mCpG sequences are favored targets for specific exogenous mutagens and carcinogens. When adjacent to another pyrimidine, 5-methylcytosine preferentially undergoes sunlight-induced pyrimidine dimer formation. Certain polycyclic aromatic hydrocarbons form guanine adducts and induce G to T transversion mutations with high selectivity at mCpG sequences.
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Affiliation(s)
- G P Pfeifer
- Division of Biology, Beckman Research Institute of the City of Hope, Duarte, CA 91010, USA.
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29
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Comeron JM. Weak selection and recent mutational changes influence polymorphic synonymous mutations in humans. Proc Natl Acad Sci U S A 2006; 103:6940-5. [PMID: 16632609 PMCID: PMC1458998 DOI: 10.1073/pnas.0510638103] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Recent large-scale genomic and evolutionary studies have revealed the small but detectable signature of weak selection on synonymous mutations during mammalian evolution, likely acting at the level of translational efficacy (i.e., translational selection). To investigate whether weak selection, and translational selection in particular, plays any role in shaping the fate of synonymous mutations that are present today in human populations, we studied genetic variation at the polymorphic level and patterns of evolution in the human lineage after human-chimpanzee separation. We find evidence that neutral mechanisms are influencing the frequency of polymorphic mutations in humans. Our results suggest a recent increase in mutational tendencies toward AT, observed in all isochores, that is responsible for AT mutations segregating at lower frequencies than GC mutations. In all, however, changes in mutational tendencies and other neutral scenarios are not sufficient to explain a difference between synonymous and noncoding mutations or a difference between synonymous mutations potentially advantageous or deleterious under a translational selection model. Furthermore, several estimates of selection intensity on synonymous mutations all suggest a detectable influence of weak selection acting at the level of translational selection. Thus, random genetic drift, recent changes in mutational tendencies, and weak selection influence the fate of synonymous mutations that are present today as polymorphisms. All of these features, neutral and selective, should be taken into account in evolutionary analyses that often assume constancy of mutational tendencies and complete neutrality of synonymous mutations.
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Affiliation(s)
- Josep M Comeron
- Department of Biological Sciences, University of Iowa, 212 Biology Building, Iowa City, IA 52242, USA.
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30
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Miller CA, Bill CA, Nickoloff JA. Characterization of palindromic loop mismatch repair tracts in mammalian cells. DNA Repair (Amst) 2004; 3:421-8. [PMID: 15010318 DOI: 10.1016/j.dnarep.2003.12.006] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/29/2003] [Indexed: 01/03/2023]
Abstract
Single- and multi-base (loop) mismatches can arise in DNA by replication errors, during recombination, and by chemical modification of DNA. Single-base and loop mismatches of several nucleotides are efficiently repaired in mammalian cells by a nick-directed, MSH2-dependent mechanism. Larger loop mismatches (> or =12 bases) are repaired by an MSH2-independent mechanism. Prior studies have shown that 12- and 14-base palindromic loops are repaired with bias toward loop retention, and that repair bias is eliminated when five single-base mismatches flank the loop mismatch. Here we show that one single-base mismatch near a 12-base palindromic loop is sufficient to eliminate loop repair bias in wild-type, but not MSH2-defective mammalian cells. We also show that palindromic loop and single-base mismatches separated by 12 bases are repaired independently at least 10% of the time in wild-type cells, and at least 30% of the time in MSH2-defective cells. Palindromic loop and single-base mismatches separated by two bases were never repaired independently. These and other data indicate that loop repair tracts are variable in length. All tracts extend at least 2 bases, some extend <12 bases, and others >12 bases, on one side of the loop. These properties distinguish palindromic loop mismatch repair from the three known excision repair pathways: base excision repair which has one to six base tracts, nucleotide excision repair which has approximately 30 base tracts, and MSH2-dependent mismatch repair, which has tracts that extend for several hundred bases.
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Affiliation(s)
- Cheryl A Miller
- Department of Molecular Genetics and Microbiology, University of New Mexico School of Medicine, Albuquerque, NM 87131, USA
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31
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Abstract
Classical genetic studies show that gene conversion can favour some alleles over others. Molecular experiments suggest that gene conversion could favour GC over AT basepairs, leading to the concept of biased gene conversion towards GC (BGC(GC)). The expected consequence of such a process is the GC-enrichment of DNA sequences under gene conversion. Recent genomic work suggests that BGC(GC) affects the base composition of yeast, invertebrate and mammalian genomes. Hypotheses for the mechanisms and evolutionary origin of such a strange phenomenon have been proposed. Most BGC(GC) events probably occur during meiosis, which has implications for our understanding of the evolution of sex and recombination.
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Affiliation(s)
- Gabriel Marais
- Institute of Cell, Animal and Population Biology, University of Edinburgh, Edinburgh EH9 3JT, Scotland, UK.
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Abstract
Recent localization of cohesin association regions along the yeast chromatin fibre suggests that compositional variability of DNA in yeast is related to the function and organization of the chromosomal loops. The bases of the loops, where the chromatin fibre is attached to the chromosomal axis, are AT-rich, bind cohesin, and are flanked by genes transcribed convergently. The hotspots of meiotic recombination are mainly found in the GC-rich parts of the loops, 'external' with respect to the chromosomal axis, frequently in the vicinity of the promoters of divergently transcribed genes. There are two possible reasons why the regions of the hotspots of recombination were enriched in GC content during evolution. One is a biased repair of recombination intermediates, and the second is a selective advantage due to an increased chromatin accessibility, which may have the carriers of GC-enriched alleles over the carriers of AT-rich alleles.
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Affiliation(s)
- Jan Filipski
- Institut J. Monod, Laboratoire de: Biochimie de la Chromatine, 2, place Jussieu, Tour 43, 75251, Paris, France.
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Marais G, Piganeau G. Hill-Robertson interference is a minor determinant of variations in codon bias across Drosophila melanogaster and Caenorhabditis elegans genomes. Mol Biol Evol 2002; 19:1399-406. [PMID: 12200468 DOI: 10.1093/oxfordjournals.molbev.a004203] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
According to population genetics models, genomic regions with lower crossing-over rates are expected to experience less effective selection because of Hill-Robertson interference (HRi). The effect of genetic linkage is thought to be particularly important for a selection of weak intensity such as selection affecting codon usage. Consistent with this model, codon bias correlates positively with recombination rate in Drosophila melanogaster and Caenorhabditis elegans. However, in these species, the G+C content of both noncoding DNA and synonymous sites correlates positively with recombination, which suggests that mutation patterns and recombination are associated. To remove this effect of mutation patterns on codon bias, we used the synonymous sites of lowly expressed genes that are expected to be effectively neutral sites. We measured the differences between codon biases of highly expressed genes and their lowly expressed neighbors. In D. melanogaster we find that HRi weakly reduces selection on codon usage of genes located in regions of very low recombination; but these genes only comprise 4% of the total. In C. elegans we do not find any evidence for the effect of recombination on selection for codon bias. Computer simulations indicate that HRi poorly enhances codon bias if the local recombination rate is greater than the mutation rate. This prediction of the model is consistent with our data and with the current estimate of the mutation rate in D. melanogaster. The case of C. elegans, which is highly self-fertilizing, is discussed. Our results suggest that HRi is a minor determinant of variations in codon bias across the genome.
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Affiliation(s)
- Gabriel Marais
- Laboratoire Biométrie et biologie évolutive, UMR CNRS 5558, Université Claude Bernard Lyon 1, Villeurbanne, France.
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Birdsell JA. Integrating genomics, bioinformatics, and classical genetics to study the effects of recombination on genome evolution. Mol Biol Evol 2002; 19:1181-97. [PMID: 12082137 DOI: 10.1093/oxfordjournals.molbev.a004176] [Citation(s) in RCA: 180] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
This study presents compelling evidence that recombination significantly increases the silent GC content of a genome in a selectively neutral manner, resulting in a highly significant positive correlation between recombination and "GC3s" in the yeast Saccharomyces cerevisiae. Neither selection nor mutation can explain this relationship. A highly significant GC-biased mismatch repair system is documented for the first time in any member of the Kingdom Fungi. Much of the variation in the GC3s within yeast appears to result from GC-biased gene conversion. Evidence suggests that GC-biased mismatch repair exists in numerous organisms spanning six kingdoms. This transkingdom GC mismatch repair bias may have evolved in response to a ubiquitous AT mutational bias. A significant positive correlation between recombination and GC content is found in many of these same organisms, suggesting that the processes influencing the evolution of the yeast genome may be a general phenomenon. Nonrecombining regions of the genome and nonrecombining genomes would not be subject to this type of molecular drive. It is suggested that the low GC content characteristic of many nonrecombining genomes may be the result of three processes (1) a prevailing AT mutational bias, (2) random fixation of the most common types of mutation, and (3) the absence of the GC-biased gene conversion which, in recombining organisms, permits the reversal of the most common types of mutation. A model is proposed to explain the observation that introns, intergenic regions, and pseudogenes typically have lower GC content than the silent sites of corresponding open reading frames. This model is based on the observation that the greater the heterology between two sequences, the less likely it is that recombination will occur between them. According to this "Constraint" hypothesis, the formation and propagation of heteroduplex DNA is expected to occur, on average, more frequently within conserved coding and regulatory regions of the genome. In organisms possessing GC-biased mismatch repair, this would enhance the GC content of these regions through biased gene conversion. These findings have a number of important implications for the way we view genome evolution and suggest a new model for the evolution of sex.
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Affiliation(s)
- John A Birdsell
- Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, Arizona 85121, USA.
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Galtier N, Piganeau G, Mouchiroud D, Duret L. GC-content evolution in mammalian genomes: the biased gene conversion hypothesis. Genetics 2001; 159:907-11. [PMID: 11693127 PMCID: PMC1461818 DOI: 10.1093/genetics/159.2.907] [Citation(s) in RCA: 318] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Bill CA, Taghian DG, Duran WA, Nickoloff JA. Repair bias of large loop mismatches during recombination in mammalian cells depends on loop length and structure. Mutat Res 2001; 485:255-65. [PMID: 11267836 DOI: 10.1016/s0921-8777(01)00065-9] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Repair of loop mismatches was investigated in wild-type and mismatch binding-defective Chinese hamster ovary (CHO) cells. Loop mismatches were formed in vivo during extrachromosomal recombination between heteroallelic plasmid substrates. Recombination was expected to occur primarily by single-strand annealing (SSA), yielding 12- or 26-base nonpalindromic loop mismatches, and 12-, 26-, or 40-base palindromic loop mismatches. Nonpalindromic loops were repaired efficiently and with bias toward loop loss. In contrast, the 12-base palindromic loop was repaired with bias toward loop retention, indicating that repair bias depends on loop structure. Among the palindromic loops, repair bias was dependent on loop length, with bias shifting from loop retention to loop loss with increasing loop size. For both palindromic and nonpalindromic loops, repair efficiencies and biases were independent of the general (MSH/MLH) mismatch repair pathway. These results are discussed with respect to the maintenance of large nonpalindromic insertions, and of small and large palindromes, in eukaryotic genomes.
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Affiliation(s)
- C A Bill
- Department of Molecular Genetics and Microbiology, University of New Mexico School of Medicine, Albuquerque, NM 87131, USA
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Affiliation(s)
- G P Pfeifer
- Department of Biology, Beckman Research Institute of the City of Hope, Duarte, CA 91010, USA.
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Lukacsovich T, Waldman AS. Suppression of intrachromosomal gene conversion in mammalian cells by small degrees of sequence divergence. Genetics 1999; 151:1559-68. [PMID: 10101177 PMCID: PMC1460558 DOI: 10.1093/genetics/151.4.1559] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Pairs of closely linked defective herpes simplex virus (HSV) thymidine kinase (tk) gene sequences exhibiting various nucleotide heterologies were introduced into the genome of mouse Ltk- cells. Recombination events were recovered by selecting for the correction of a 16-bp insertion mutation in one of the tk sequences. We had previously shown that when two tk sequences shared a region of 232 bp of homology, interruption of the homology by two single nucleotide heterologies placed 19 bp apart reduced recombination nearly 20-fold. We now report that either one of the nucleotide heterologies alone reduces recombination only about 2.5-fold, indicating that the original pair of single nucleotide heterologies acted synergistically to inhibit recombination. We tested a variety of pairs of single nucleotide heterologies and determined that they reduced recombination from 7- to 175-fold. Substrates potentially leading to G-G or C-C mispairs in presumptive heteroduplex DNA (hDNA) intermediates displayed a particularly low rate of recombination. Additional experiments suggested that increased sequence divergence causes a shortening of gene conversion tracts. Collectively, our results suggest that suppression of recombination between diverged sequences is mediated via processing of a mispaired hDNA intermediate.
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Affiliation(s)
- T Lukacsovich
- Department of Biological Sciences, University of South Carolina, Columbia, South Carolina 29208, USA
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