Stem cells are crucial for organogenesis and maintenance of healthy tissues. They also have potential use in stem cell therapies and regenerative medicine. Yet, our understanding of how stem cells develop during organ formation is limited. Drosophila testes provide one of the most tractable, and thoroughly characterized systems for studying stem cell behavior. The stem cell niche that forms in the testis is a model for the microenvironments present in other organs where there is an asymmetrically dividing population of stem cells. In the testis niche, cyst stem cells (CySCs) and germline stem cells (GSCs) are arrayed around somatic hub cells. Signaling from hub cells regulates the equilibrium of stem cell maintenance and differentiation. The Wawersik Lab has shown that the Jak-STAT signaling pathway is necessary and sufficient for CySC maintenance shortly after GSC establishment (Wawersik et al. 2012). However, the function of downstream mediators of the Jak-STAT pathway are not entirely known. One of these downstream mediators is chinmo (Bach et al, 2011). In the adult Drosophila testis, chinmo has been shown to be required for maintenance of cyst stem cells (CySC) (Bach et al, 2011). Additionally, chinmo is responsible for maintenance of male sexual identity of CySCs in the adult testis (Ma, Wawersik, Matunis, 2014). Prior studies have not assessed chinmo expression or function during development. This thesis will study chinmo\u27s role in CySC maintenance and the initial determination of male sexual identity in Drosophila gonad during the embryonic and larval development. Specifically, the temporal and spatial expression of chinmo was characterized in developing gonads. Loss and gain of function studies were also performed. Results indicate that chinmo is both necessary and sufficient for establishment, but not maintenance, of functional CySCs in the developing testis. These data suggest that chinmo has a different function in CySCs during development then in an adult Drosophila testis
