Cohesin Is Limiting for the Suppression of DNA Damage–Induced Recombination between Homologous Chromosomes

Brandeis University, United States of America
PLoS Genetics (Impact Factor: 7.53). 07/2010; 6(7):e1001006. DOI: 10.1371/journal.pgen.1001006
Source: PubMed


Double-strand break (DSB) repair through homologous recombination (HR) is an evolutionarily conserved process that is generally error-free. The risk to genome stability posed by nonallelic recombination or loss-of-heterozygosity could be reduced by confining HR to sister chromatids, thereby preventing recombination between homologous chromosomes. Here we show that the sister chromatid cohesion complex (cohesin) is a limiting factor in the control of DSB repair and genome stability and that it suppresses DNA damage-induced interactions between homologues. We developed a gene dosage system in tetraploid yeast to address limitations on various essential components in DSB repair and HR. Unlike RAD50 and RAD51, which play a direct role in HR, a 4-fold reduction in the number of essential MCD1 sister chromatid cohesion subunit genes affected survival of gamma-irradiated G(2)/M cells. The decreased survival reflected a reduction in DSB repair. Importantly, HR between homologous chromosomes was strongly increased by ionizing radiation in G(2)/M cells with a single copy of MCD1 or SMC3 even at radiation doses where survival was high and DSB repair was efficient. The increased recombination also extended to nonlethal doses of UV, which did not induce DSBs. The DNA damage-induced recombinants in G(2)/M cells included crossovers. Thus, the cohesin complex has a dual role in protecting chromosome integrity: it promotes DSB repair and recombination between sister chromatids, and it suppresses damage-induced recombination between homologues. The effects of limited amounts of Mcd1and Smc3 indicate that small changes in cohesin levels may increase the risk of genome instability, which may lead to genetic diseases and cancer.

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    • "One possible explanation for this ‘hyper-rec’ phenotype associated with the replication checkpoint mutants is a role for Mrc1 in promoting sister chromatid cohesion in S. cerevisiae (54). As sister chromatid cohesion limits recombination between homologous chromosomes (55), disrupting sister chromatid cohesion through such mutations could facilitate increased levels of interchromosomal GC. "
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    ABSTRACT: DNA double-strand breaks (DSBs) can cause chromosomal rearrangements and extensive loss of heterozygosity (LOH), hallmarks of cancer cells. Yet, how such events are normally suppressed is unclear. Here we identify roles for the DNA damage checkpoint pathway in facilitating homologous recombination (HR) repair and suppressing extensive LOH and chromosomal rearrangements in response to a DSB. Accordingly, deletion of Rad3ATR, Rad26ATRIP, Crb253BP1 or Cdc25 overexpression leads to reduced HR and increased break-induced chromosome loss and rearrangements. We find the DNA damage checkpoint pathway facilitates HR, in part, by promoting break-induced Cdt2-dependent nucleotide synthesis. We also identify additional roles for Rad17, the 9-1-1 complex and Chk1 activation in facilitating break-induced extensive resection and chromosome loss, thereby suppressing extensive LOH. Loss of Rad17 or the 9-1-1 complex results in a striking increase in break-induced isochromosome formation and very low levels of chromosome loss, suggesting the 9-1-1 complex acts as a nuclease processivity factor to facilitate extensive resection. Further, our data suggest redundant roles for Rad3ATR and Exo1 in facilitating extensive resection. We propose that the DNA damage checkpoint pathway coordinates resection and nucleotide synthesis, thereby promoting efficient HR repair and genome stability.
    Nucleic Acids Research 03/2014; 42(9). DOI:10.1093/nar/gku190 · 9.11 Impact Factor
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    • "Particularly relevant is exposure of cells to DNA damage, which can activate dormant cohesin molecules (Strom et al. 2004, 2007; Unal et al. 2004, 2007, 2008). Since cohesin mutants show defects in homologous recombination (Covo et al. 2010; Sjogren and Strom 2010) and since defects in resolution of recombination intermediate can lead to chromosome gain (Ho et al. 2010; Rodrigue et al. 2012) the effects of DNA damage and the role of homologous recombination on chromosome gain in WT and SCC defective strains were studied. We examined chromosome gain following growth of diploid MATa/MATa cells on plates containing a low level of the recombinogen methyl methanesulfonate (MMS; 1 mM). "
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    ABSTRACT: Gain or loss of chromosomes resulting in aneuploidy can be important factors in cancer and adaptive evolution. Although chromosome gain is a frequent event in eukaryotes, there is limited information on its genetic control. Here we measured the rates of chromosome gain in wild type yeast and sister chromatid cohesion (SCC) compromised strains. SCC tethers the newly replicated chromatids until anaphase via the cohesin complex. Chromosome gain was measured by selecting and characterizing copper resistant colonies that emerged due to increased copies of the metallothionein gene CUP1. Although all defective SCC diploid strains exhibited increased rates of chromosome gain, there were 15-fold differences between them. Of all mutants examined, a hypomorphic mutation at the cohesin complex caused the highest rate of chromosome gain while disruption of WPL1, an important regulator of SCC and chromosome condensation, resulted in the smallest increase in chromosome gain. In addition to defects in SCC, yeast cell type contributed significantly to chromosome gain, with the greatest rates observed for homozygous mating type diploids, followed by heterozygous mating type and smallest in haploids. In fact, wpl1 deficient haploids did not show any difference in chromosome gain rates compared to WT haploids. Genomic analysis of copper-resistant colonies revealed that the "driver" chromosome for which selection was applied could be amplified to over 5 copies per diploid cell. In addition, an increase in the expected "driver" chromosome was often accompanied by a gain of a small number of other chromosomes. We suggest that while chromosome gain due to SCC malfunction can have negative effects through gene imbalance, it could also facilitate opportunities for adaptive changes. In multicellular organisms, both factors could lead to somatic diseases including cancer.
    Genetics 12/2013; 196(2). DOI:10.1534/genetics.113.159202 · 5.96 Impact Factor
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    • "This growth advantage was not observed in the diploid, supporting the contention that it is indeed a function of tetraploid-specific pathway activation. Previously, three regulatory processes were shown to be essential specifically in tetraploids – homologous recombination, kinetochore function, and spindle chromatid cohesion [27,62], and our findings suggest that the CWI pathway is a fourth essential process. "
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    ABSTRACT: In the model eukaryote, Saccharomyces cerevisiae, previous experiments have identified those genes that exert the most significant control over cell growth rate. These genes are termed HFC for high flux control. Such genes are overrepresented within pathways controlling the mitotic cell cycle. We postulated that the increase/decrease in growth rate is due to a change in the rate of progression through specific cell cycle steps. We extended and further developed an existing logical model of the yeast cell cycle in order elucidate how the HFC genes modulated progress through the cycle. This model can simulate gene dosage-variation and calculate the cycle time, determine the order and relative speed at which events occur, and predict arrests and failures to correctly execute a step. To experimentally test our model's predictions, we constructed a tetraploid series of deletion mutants for a set of eight genes that control the G2/M transition. This system allowed us to vary gene copy number through more intermediate levels than previous studies and examine the impact of copy-number variation on growth, cell-cycle phenotype, and response to different cellular stresses. For the majority of strains, the predictions agreed with experimental observations, validating our model and its use for further predictions. Where simulation and experiment diverged, we uncovered both novel tetraploid-specific phenotypes and a switch in the determinative execution point of a key cell-cycle regulator, the Cdc28 kinase, from the G1/S to the S/G2 boundaries.
    BMC Genomics 10/2013; 14(1):744. DOI:10.1186/1471-2164-14-744 · 3.99 Impact Factor
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