Epigenetic regulation of spermatogenesis and transgenerational epigenetic inheritance
AuthorKlukovich, Rachel Alexa
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Epigenetics is defined as genomic modifications that alter gene expression without changing the nucleic acid sequence. These modifications come in hundreds of forms and affect both DNA and RNA. Recently, the field of epigenetics has taken to studying two newfound gene expression regulators: the highly abundant and universal N6-methyladenosine modification, and noncoding RNAs. N6-methyladenosine (m6A) has been implicated as a reversible, RNA modification that can cause infertility and other defects when not properly regulated. Noncoding RNAs have also been recently implicated as critical mediators of gene expression control with their ability to alter transcript stability and remodel chromatin. Other epigenetic factors, including noncoding RNAs, can become differentially expressed and transgenerational via epigenetic transgenerational inheritance with the ill effects lasting for generations. Abnormally regulated or persistent epigenetic modifications have been implicated in causing a variety of undesirable phenotypes such as infertility. To better understand the epigenetic causes of male infertility, this dissertation investigates the phenotype and mechanism of improper m6A regulation due to lack of an m6A-specific demethylase, ALKBH5, using a knockout mouse model (Chapter II). The reproductive health of male mice was monitored throughout development, and m6A RNA-immunoprecipitation and sequencing was performed at four different stages of spermatogenesis to follow transcript fate. The knockout mouse model had a delay in meiotic progression starting at P14 that led to high levels of spermatogenic apoptosis in the adult testis. In addition, there was a correlation between increased splicing events, high m6A levels, and transcript degradation in the knockout. It was concluded that m6A acts in a biphasic manner: in the nucleus, it guides splicing events of pre-mRNAs while in the cytoplasm, it marks transcripts’ 3’UTR for degradation. Then, this dissertation investigates environmentally induced epigenetic causes of prostate disease using a rat model (Chapter III). Pregnant rats were transiently exposed to vinclozolin, and the F3 generation’s prostate stroma and epithelium were examined for epigenetic transgenerational inheritance of differentially expressed epigenetic factors, including noncoding RNAs and differential DNA methylation regions (DMRs). Both noncoding RNAs and the DMRs were found to be differentially expressed with many modifications altered intergenically. DMRs overlapped with the affected genes in both cell types indicating that they may be the primary mediators of transgenerational epigenetic inheritance. The small, noncoding RNAs were found to overlap significantly with the mRNAs in the prostate stroma. Because the modifications were distinct in both the prostate stroma and epithelium, this indicates that ancestral exposure can have different effects on different cell types within the same organ. Together, this dissertation gives a comprehensive overview of the epigenetic regulation of spermatogenesis and transgenerational epigenetic inheritance.