Geyer, Christopher BJohnson, Taylor A2023-02-102022-122022-12-05December 2http://hdl.handle.net/10342/12269Spermatogenesis, the male germ cell maturation process, allows men to become and remain fertile for decades. Male fertility relies on fate decisions of different types of spermatogonia – spermatogonial stem cells maintain the germline long-term, undifferentiated progenitor spermatogonia divide and await the differentiation signal (retinoic acid, RA), and differentiating spermatogonia proceed forward into meiosis as spermatocytes to ultimately become sperm. Spermatogonial differentiation and meiotic initiation are indispensable transitions in spermatogenesis that remain poorly understood. The three studies within this dissertation, using a combination of in vivo and in vitro approaches, detail spermatogonial requirements in these two transitions. The first study (chapter two) scrutinizes and redefines a presumed dogma – the requirement of RA for the spermatogonia-to-spermatocyte (mitotic-to-meiotic) transition. The second study (chapter three) deciphers the differential responsiveness of spermatogonia to RA in the adult testis. The third study (chapter four) introduces a novel RNA binding protein required for the commitment to and completion of spermatogonial differentiation. The collective findings from these three studies both enrich our understanding of spermatogonial biology and propose avenues for treatments that can enhance or discontinue spermatogonial differentiation.application/pdfenSpermatogenesisRetinoic AcidRAGerm CellMeiosisSpermatozoaSpermatogoniaHumansMaleFemaleDoctoral Dissertation2023-01-31