Effects of oxidative stress on mitotic recombination and genomic stability in yeast after 20 passages
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ABSTRACT:
ORGANISM(S): Saccharomyces cerevisiae
PROVIDER: GSE107178 | GEO | 2017/11/21
SECONDARY ACCESSION(S): PRJNA419211
REPOSITORIES: GEO
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Project description:Oxidative stress is a common factor threating genomic stability in almost all aerobic organisms. Using a yeast screening system, we measured the frequency of mitotic recombination was greatly elevated after H2O2 treatment. H2O2 was able to break chromatid directly in G1 synchronized cells and homologous recombination was induced to repair DNA double stand breaks at S/G2 phase. By whole genome SNP microarray and sequencing, the patterns of H2O2 induced loss of heterozygosity (LOH; gene conversion and crossover), chromosomal rearrangement, and aneuploidy changes were revealed. LOH events were the most common genomic alterations induced by H2O2 and were randomly distributed throughout the genome.
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Project description:Mitotic recombination between homologous chromosomes can lead to loss-of-heterozygosity (LOH), which is an important contributor to human disease. In the current study, a defined double-strand break (DSB) on chromosome IV was used to initiate LOH in a yeast strain with sequence-diverged chromosomes. Associated gene conversion tracts, which reflect the repair of mismatches formed when diverged chromosomes exchange single strands, were mapped using microarrays. LOH events reflected two broken chromosomes, one of which was repaired as a crossover and the other as a noncrossover.
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Project description:When loss of heterozygosity (LOH) is correlated with loss or gain of disease phenotype, it is often necessary to identify which gene or genes are involved. Here, we generated a region-specific LOH-inducing system based on mitotic crossover in human induced pluripotent stem cells (hiPSCs). We first tested our system on chromosome 19. To detect homozygous clones generated by LOH, a positive selection cassette was inserted at the AASV1 locus of chromosome 19. LOHs were generated by the combination of allele-specific double-stranded DNA breaks introduced by CRISPR/Cas9 and suppression of Bloom syndrome (BLM) gene expression by the Tet-Off system. The BLM protein inhibitor, ML216, exhibited a similar crossover efficiency and distribution of crossover sites. We next applied this system to the short arm of chromosome 6 where human leukocyte antigen (HLA) loci are located. Genotyping and fluorescence-activated cell sorting analysis demonstrated that LOHs associated with chromosomal crossover occurred at the expected positions. Thus, HLA-homozygous hiPSCs generated from parental cells may help to mitigate a current shortcoming of hiPSC-based transplantation related to the immunological differences between donor and host. In conclusion, the system described in this study would greatly facilitate not only the genetic analysis of hiPSCs but also hiPSCs-based regenerative medicine.
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Project description:Genome modification in mouse embryonic stem cells (mESCs) has provided the versatile platform to analyzing gene functions in mammalian cells. Bloom helicase-deficient mESCs showed elevated rate of loss of heterozygosity (LOH) through mitotic recombination. By utilizing this characteristic of Blm deficiency, we established an efficient method to introduce homozygous mutations into mESCs, which can be used for phenotype-driven recessive screen. It is generally thought that mitotic recombination is initiated by double-strand break. DNA repair machinery, however, possesses mechanisms that suppress deleterious crossovers between homologous chromosomes. Bloom helicase plays a central role to suppress such crossover; hence its deficiency causes elevated frequency of mitotic recombination. To directly answer if DSB can initiate mitotic recombination, we established a reporter cell line, in which the recognition site of I-SceI endonuclease was introduced in the Aprt gene in Blm-deficient mESCs. We used two types of I-SceI expression vectors; one expresses a mammalian codon-optimized I-SceI (ISceIo) and the other expresses I-SceIo fused with N-terminal 110-amino acids of Geminin (Gemi). Geminin-fused I-SceI can be stabilized only in lateS/G2 phase. After I-SceI transfection and subsequent selection, we isolated Aprt-deficient mutants. Half of the mutants showed LOH in the whole telomeric region from I-SceI site, but the other half showed local LOH near the I-SceI site. Further analyses suggested that large deletion was introduced and caused LOH, which was not seen in spontaneous LOH. We designed CGH probes in 300-bp resolution in 8Mb telomeric region of chr 8 (The Aprt gene locates 7Mb from the telomere) to map the deleted regions in these mutants.
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Project description:Meiotic crossover formation requires the stabilization of early recombination intermediates by a set of proteins and occurs within the environment of the chromosome axis, a structure important for the regulation of meiotic recombination events. The molecular mechanisms underlying and connecting crossover recombination and axis localization are elusive. Here, we identified the ZZS (Zip2–Zip4–Spo16) complex, required for crossover formation, which carries two distinct activities: one provided by Zip4, which acts as hub through physical interactions with components of the chromosome axis and the crossover machinery, and the other carried by Zip2 and Spo16, which preferentially bind branched DNA molecules in vitro. We found that Zip2 and Spo16 share structural similarities to the structure-specific XPF–ERCC1 nuclease, although it lacks endonuclease activity. The XPF domain of Zip2 is required for crossover formation, suggesting that, together with Spo16, it has a noncatalytic DNA recognition function. Our results suggest that the ZZS complex shepherds recombination intermediates toward crossovers as a dynamic structural module that connects recombination events to the chromosome axis. The identification of the ZZS complex improves our understanding of the various activities required for crossover implementation and is likely applicable to other organisms, including mammals.
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Project description:Development of primary mediastinal B-cell lymphoma (PMBL) is driven by cumulative genomic aberrations. It is unknown whether copy-neutral loss of heterozygosity (CN-LOH) contributes to the pathogenesis of this tumor. To get insight into the CN-LOH landscape of PMBL, we performed Single Nucleotide Polymorphism array (SNPa) analysis of two PMBL-derived cell lines and 33 primary tumors. The study uncovered large-scale CN-LOH lesions in both cell lines and 90.9% (30/33) of primary tumors. The latter cases showed 133 CN-LOH stretches of size >25Mb which affected up to 14 chromosomes per case (mean of 4.4). Involvement of chromosomal segments was predominant (81.2%), which, in a heterozygous diploid context, suggests the implication of B-cell specific crossover events. Further analysis indicated that the CN-LOH lesions were triggered by one or two consecutive molecular hits. Notably, CN-LOH segments were non-randomly clustered on chromosome 6p (60%), 15 (37.2%) and 17q (40%). Preliminary whole-exome sequencing data yielded coincidence of these lesions with mutations in MHC I and histon-related genes (6p21), B2M (15q15) and GNA13 (17q23), respectively. We hypothesize that CN-LOH-associated hits occurred early during lymphomagenesis, following mutagenesis but preceding genomic gains. Screening of the cohort of 2,658 cancer whole-genomes revealed that the CN-LOH landscape in PMBL is unique and distinguishes this tumor from other malignancies. Altogether, CN-LOH lesions rank as the most frequent genetic defect identified so far in this disease and the CN-LOH landscape suggest a hitherto undescribed mitotic recombinational driver. The aberrations affect the expression of key driver genes and functionally alternate genomic deletions which are infrequent in PMBL.
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Project description:Several protein ensembles facilitate meiotic crossover recombination and the associated process of synaptonemal complex (SC) assembly during meiosis. We have employed proximity labeling as a phenotyping tool to investigate functional requirements for spatial relationships between meiotic recombination and SC proteins in S. cerevisiae, and to gain deeper insight into the molecular deficits of crossover-deficient meiotic mutants. We find that recombination initiation and synaptonemal complex structures are dispensable for proximity labeling of the Zip3 E3 ligase by components of the ZZS ensemble (Zip2, Zip4 and Spo16) but enzymes associated with early steps in recombination are required for Zip3 proximity labeling by MutSg, consistent with the possibility that MutSg joins Zip3 only after a specific recombination intermediate has been generated. Proximity labeling furthermore suggests that a key defect of crossover-defective, SC-proficient zip1 separation-of-function mutants is a failure to assemble an early recombination ensemble where MutSg can properly engage Zip3. We also find that the SC structural protein Ecm11 is proximity labeled by ZZS proteins in a Zip4-dependent and Zip1-independent manner, but by Zip3 and Msh4 at least in part via a distinct pathway that relies on Zip1. Finally, streptavidin pulldown followed by mass spectrometry on eleven proximity labeling strains uncovered shared proximity targets of SC and crossover-associated proteins, some of which have not yet been implicated in meiotic recombination or SC formation highlighting the potential of proximity labeling as a discovery tool.
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Project description:Calorie restriction (CR) is known to decrease not only spontaneous but also chemical carcinogen and radiation-induced carcinogenesis. However, the biological mechanisms for the anti-cancer effect of CR remain unclear. In this study, analyzed and compared with genomic alterations in thymic lymphoma (TL) arising after irradiation between with or without CR. The frequency of point mutations at Pten locus on chromosome 19 was not different between 95 kcal and 65 kcal groups, but the frequency of LOH with DNA copy number change in 65 kcal group tended to be higher than 95 kcal group. On chromosome 4 and 11, the LOH frequency was not different between 95 kcal and 65kcal groups, but the LOH mechanism was different. In 65 kcal group, the frequency of LOH without DNA copy number change by chromosome mis-segregation or mitotic recombination was lower than 95 kcal group, but then the frequency of LOH with DNA copy number change by deletion was higher than 95 kcal group. The frequency of genomic alterations such as LOH and point mutation at Ikaros on chromosome 11 were observed as high as 70% (19 / 27) in 95 kcal group and 76% (16 / 21) in 65 kcal group. However, the mechanisms of LOH and Ikaros inactivation are different between 95 kcal and 65 kcal group.
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Project description:The Saccharomyces cerevisae RAD3 gene is homolog of human XPD, an essential gene encoding a DNA helicase of the TFIIH complex involved in both nucleotide excision repair (NER) and transcription. Mutant alleles of RAD3 have been identified (rad3-101 and rad3-102) that have partial defects in DNA repair associated with a strong hyper-recombination (hyper-Rec) phenotype. Previous studies showed that the hyper-Rec phenotype associated with rad3-101 and rad3-102 can be explained as a consequence of persistent single-stranded DNA gaps that are converted to recombinogenic double-strand breaks (DSBs) by replication. We have further characterized these events using a system in which the reciprocal products of mitotic recombination between homologs are recovered as red and white sectored colonies. Both rad3-101 and rad3-102 elevate the frequency of sectored colonies about 100-fold. Subsequent mapping of these events shows that three-quarters of crossovers between homologs induced in hyper-Rec rad3 mutants reflect DSBs formed in at the same positions in both sister chromatids (double sister-chromatid breaks, DSCBs). The remainder reflects DSBs formed in single chromatids (single chromatid breaks, SCBs). The ratio of DSCBs to SCBs is similar to that observed for spontaneous recombination events in wild-type cells. In addition to examining crossovers on chromosome V, we mapped 216 unselected genomic alterations throughout the genome including crossovers, gene conversions, deletions, and duplications. We found a significant association between the location of these recombination events and regions with elevated gamma-H2AX. In addition, there was a hotspot for deletions and duplications at the IMA2 and HXT11 genes near the left end of chromosome XV. A comparison of these data with our previous analysis of spontaneous mitotic recombination events suggests that a sub-set of spontaneous events in wild-type cells may be initiated by incomplete NER reactions, and that DSCBs, which cannot be repaired by sister-chromatid recombination, are a major source of mitotic recombination between homologous chromosomes.
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