Biology Theses and Dissertations

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Browsing Biology Theses and Dissertations by Subject "aging"

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    Molecular Mechanisms of Homolog-Independent DNA Repair During C. Elegans Meiosis
    (University of Oregon, 2022-10-04) Toraason, Erik; Libuda, Diana
    Meiosis is the specialized cell division by which most sexually reproducing organisms generate haploid gametes such as sperm and eggs. Meiotic cells of diploid organisms contain four copies of the genome: two homologous chromosomes as well as identical replicates of each homolog called sister chromatids. Although DNA damage threatens genomic stability, meiotic cells intentionally induce DNA double-strand breaks (DSBs) across the genome. Most studies of meiotic DSB repair have focused on how a limited subset of DSBs are resolved with the homologous chromosome as crossovers, which are required for accurate meiotic chromosome segregation. The remaining DSBs that are not repaired with the homologous chromosome have been long hypothesized in metazoans to be repaired using the sister chromatid. The perfect identity shared by sister chromatids, however, has precluded testing of this model by sequencing approaches. To directly detect the long-hypothesized homolog-independent recombination events during metazoan meiosis, I developed an ‘intersister/intrachromatid repair assay’ (ICR assay) in the nematode Caenorhabditis elegans which enables the direct detection of homolog-independent crossover and noncrossover recombination during meiosis. Using the ICR assay, I demonstrate that the sister chromatid or same DNA molecule can indeed be engaged to repair DSBs as crossovers or noncrossovers, and that intersister/intrachromatid repair is the sole recombination pathway utilized in late meiotic prophase I. Additionally, using the ICR assay in conjunction with cytological and functional DSB repair assays, I show that the highly conserved structural maintenance of chromosomes 5/6 complex (SMC-5/6) and tumor suppressor BRCA1 (BRC-1) restrict intersister crossover recombination and error-prone repair during meiotic prophase I. Finally, I investigated how meiotic DNA repair is impacted during germline aging. Utilizing a computational image analysis pipeline I developed, I find that sperm depletion causes reduced DSB induction, while processes associated with germline aging contribute to DNA repair defects in aged germlines. Moreover, I identify the ubiquitin ligase-like protein UEV-2 as a putative regulator of DNA repair defects during aging. Taken together, my thesis work illuminates mechanisms regulating metazoan intersister/intrachromatid meiotic recombination and defines pathways balancing efficiency and accuracy of DNA repair in the immortal germline.