| Abstract |
Sexual reproduction across many species requires intimate, lifelong cell-cell interactions between somatic and germline cell lineages within the gonad. The formation of specialized haploid cells (sperm or egg) is known as gametogenesis. This process only occurs within gonadal tissues, necessitating a unique cellular microenvironment called a niche, which contains stem cell renewal signals as well as instructional cues for differentiation. Rising evidence suggests that defects in various functions of somatic support cells--essential components of the niche--are the root cause of many cases of infertility in humans. For this reason, many research initiatives have leveraged animal models with highly conserved germline biology to investigate a fundamental question: How is a healthy egg or sperm made? Using the Drosophila testis stem cell niche as a model system, we have utilized a combination of live and fixed analyses to investigate the role of somatic cyst stem cells (CySCs) and their daughter cyst cells in facilitating germline homeostasis. Outlined in this thesis are three key findings: 1. Somatic cell behavior is highly dynamic prior to stable germline encystment. 2. Acute mating stress results in loss of critical soma-germline contact that may allow for plasticity in the niche to compensate for continuous demand on the tissue. 3. Loss of male somatic sex identity allows acquisition of female-specific cell behaviors and instructs non-autonomous cell-fate changes in the underlying XY germ cells. This work represents the first time somatic cells have been carefully studied with live imaging, an approach that continues to reveal critical cellular dynamics overlooked by fixed analyses. Ultimately, our findings support a model whereby somatic cells are critical regulators of germline homeostasis.
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