Genetic analysis of the cell biological basis of sperm morphogenesis.

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The overall goal of my research is to understand how cells and tissues develop their complex 3-D architecture through the process of morphogenesis. A key model my lab uses to study morphogenesis is spermatogenesis, the process of producing sperm. Spermatogenesis produces one of the most specialized and architecturally complex cells in animals and is a dynamic developmental process wherein the germline undergoes 3 controlled morphogenetic transitions between discrete stages: from mitotic spermatogonia to meiotic spermatocytes, from meiotic spermatocytes to spermatids, and from spermatids to mature spermatozoa. The NSERC funded research program I propose employs genetic approaches to investigate the developmental program of spermatogenesis. To date, the precise role of the soma in mediating the developmental program of spermatogenesis has not been systematically explored. To address this we recently carried out a large genetic screen to identify genes that are required in the somatic cells of Drosophila testis for sperm development. Our lab uses the fly testes as a model since they provide an excellent genetically tractable in vivo model system to explore spermatogenesis. Our genetic screen, the largest of its kind carried out to date, identified genes required in somatic cells for fertility. Over 2500 single RNAi lines representing over 2000 genes were screened. The phenotype of candidate genes was analysed in detail to determine when spermatogenesis arrested. Bioinformatic analysis uncovered several functional gene classes that were over-represented in our collection of candidates. Importantly, particular gene classes were associated with specific developmental transitions. For example genes associated with endocytosis, cell polarity, and microtubule-based transport corresponded with the development of spermatogonia, spermatocytes, and spermatids, respectively. My NSERC proposal will provide detailed mechanistic insight into sperm development: We will functionally characterize the gene networks that act in the soma to mediate the developmental transitions from mitotic spermatogonia to meiotic spermatocytes, from meiotic spermatocytes to spermatids, and from spermatids to mature spermatozoa. This will reveal the mechanism by which each specific gene network contributes to these transitions. Our main aims are: a) Using a combination of genetics and live imaging we will determine the role of endocytotic regulators in the soma in modulating cell-signals that regulate spermatogonial development. b) Using a combination of genetics and live imaging we will determine the role of cell polarity genes in the soma in the morphogenetic events that underlie spermatocyte development. c) Using a combination of genetics and live imaging we will elucidate the role of molecular motors and microtubule-based transport in the soma during spermatid morphogenesis.