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Abstract
The accuracy of meiotic division in oocytes as well as mitotic divisions post-fertilization are critical for maintaining genomic stability in developing embryos. This dissertation was conducted to investigate the effect of prevalent environmental contaminants, bisphenol A (BPA) and bisphenol F (BPF) on mature mouse oocyte and pre-implantation embryo development. The studies in Chapter 2 focused ovulated metaphase-II oocytes and demonstrated that brief exposure (4h) to increasing concentrations (5, 25, 50 µg/mL) of BPA and BPF disrupt the assembled meiotic spindle in a dose-dependent manner. Bisphenol exposure lead to aberrant spindle structure, characterized by very short spindle and highly unfocused poles with fragmented pericentrin (Pcnt)-labelled aMTOCs. Live cell imaging, microtubule (MT) regrowth, and immunofluorescence analysis of the oocytes revealed microtuble-disrupting activity by bisphenols, and pointed to differences the mechanism of action by BPA and BPF. Moreover, we identified a potential interaction between Bisphenol action and the Aurora Kinase A (AURKA) pathway as inhibition the AURKA activity limited bisphenol-mediated distuption of the spindle poles. In subsequent studies (Chapter 3), mouse preimplantation embryos were cultured with BPA or BPF at specific time points (4, 48, 53, 71h) post-fertilization, corresponding to key developmental transitions. At each stage, the bisphenol compounds were disruptive to embryonic development. Surprisingly, BPF was more detrimental, relative to BPA, with few embryos reaching the blastocyst stage. BPA exposure shortly after fertilization delayed the first mitotic cleavage, while the same dose of BPF completely blocked it. The impact on mitotic division may be attributed to microtubule disrupting activity. Notably, subsequent embryo development was impaired even after bisphenol removal. Our analysis revealed mitotic defects, skewed cell lineage specification, and disrupted actomyosin network in the embryos that reached the blastocyst stage. Actomyosin involved in cell polarity and actin zippering during compaction, as well as blastocyst hatching were also disrupted by BPA and BPF. Moreover, we observed altered YAP1 distribution in blastomeres, indicating that bisphenols may effect HIPPO signaling that regulates cell lineage specification. Taken together, the studies in this dissertation support that brief BPA and BPF exposure disrupts essential cytoskeletal networks, which is highly detrimental to oocyte spindle stability and preimplantation embryo development.