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Topoisomerases modulate the timing of meiotic DNA breakage and chromosome morphogenesis in Saccharomyces cerevisiae

ABSTRACT: During meiotic prophase, concurrent transcription, recombination, and chromosome synapsis place substantial topological strain on chromosomal DNA, but the role of topoisomerases in this context remains poorly defined. Here, we analyzed the roles topoisomerases I and II (Top1 and Top2) during meiotic prophase in Saccharomyces cerevisiae. We show that both topoisomerases accumulate primarily in promoter-containing intergenic regions of actively transcribing genes, including many meiotic double-strand break (DSB) hotspots. Despite the comparable binding patterns, top1 and top2 mutations have different effects on meiotic recombination. TOP1 disruption delays DSB induction and shortens the window of DSB accumulation by an unknown mechanism. By contrast, temperature-sensitive top2-1 mutants exhibit a marked delay in meiotic chromosome remodeling and elevated DSB signals on synapsed chromosomes. The problems in chromosome remodeling were linked to altered Top2 binding patterns rather than a loss of Top2 catalytic activity and stemmed from a defect in recruiting the chromosome remodeler Pch2/TRIP13 to synapsed chromosomes. No chromosomal defects were observed in the absence of TOP1. Our results imply independent roles for topoisomerases I and II in modulating meiotic chromosome structure and recombination.

ORGANISM(S): Saccharomyces cerevisiae

PROVIDER: GSE131994 | GEO | 2020/03/06

REPOSITORIES: GEO

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Project description:DNA double strand breaks (DSBs) in repetitive sequences are a potent source of genomic instability, due to the possibility of non-allelic homologous recombination (NAHR). Repetitive sequences are especially at risk during meiosis, when numerous programmed DSBs are introduced into the genome to initiate meiotic recombination 1. Within the budding yeast repetitive ribosomal (r)DNA array, meiotic DSB formation is prevented in part through Sir2-dependent heterochromatin 2,3. Here, we demonstrate that the edges of the rDNA array are exceptionally susceptible to meiotic DSBs, revealing an inherent heterogeneity within the rDNA array. We find that this localised DSB susceptibility necessitates a border-specific protection system consisting of the meiotic ATPase Pch2 and the origin recognition complex subunit Orc1. Upon disruption of these factors, DSB formation and recombination specifically increased in the outermost rDNA repeats, leading to NAHR and rDNA instability. Strikingly, the Sir2-dependent heterochromatin of the rDNA itself was responsible for the induction of DSBs at the rDNA borders in pch2? cells. Thus, while Sir2 activity globally prevents meiotic DSBs within the rDNA, it creates a highly permissive environment for DSB formation at the heterochromatin/euchromatin junctions. Heterochromatinised repetitive DNA arrays are abundantly present in most eukaryotic genomes. Our data define the borders of such chromatin domains as distinct high-risk regions for meiotic NAHR, whose protection may be a universal requirement to prevent meiotic genome rearrangements associated with genomic diseases and birth defects. This SuperSeries is composed of the following subset Series: GSE30071: ssDNA mapping in dmc1 strains GSE30072: ChIP-chip of DSB factors in wild type and pch2 strains Two types of study were undertaken to understand the regulation of meiotic DSB formation close to repetitive DNA elements in yeast. First, DSBs were mapped using ssDNA enrichment in strains isogenic for a dmc1 mutation, and also including pch2 delete, orc1-161, rdna delete and a reciprocal translocation between chromosomes 2 and 12 (trans2to12). Second, the association of the DSB factors Hop1, Rec114, Mer2, and Mre1, as well as total histone H3 and H3K4-trimethylation were measured by ChIP-chip analysis in wild-type and pch2 delete strains.

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Topoisomerases modulate the timing of meiotic DNA breakage and chromosome morphogenesis in Saccharomyces cerevisiae

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