Genetic dissection of meiotic cytokinesis in Drosophila melanogaster males

Studies in a variety of organisms indicate that membrane traffic to the cleavage furrow is an essential facet of cytokinesis involving components of the secretory and endocytic/recycling trafficking pathways, as well as the membrane fusion machinery. My PhD project focused around the characterization of two genes required for cleavage furrow formation and ingression in male meiotic cells namely sauron and Cog7 which encode the Drosophila orthologues of two known players of membrane trafficking pathways. Sauron is the Drosophila orthologue of Golgi phosphoprotein 3 (GOLPH3) which has recently been recognized as a potent oncogene amplified in many human cancers. Studies in both yeast and mammalian cells have implicated this protein in several vesicle trafficking events. I show that Sau/dGOLPH3 is required during the early steps of spermatocyte cytokinesis playing an essential role in both contractile ring assembly and vesicle trafficking during furrow ingression. Consistently my work suggests that Sau/dGOLPH3 might interact with components of both the contractile apparatus and the membrane trafficking machinery in male germ cells. The conserved oligomeric Golgi (COG) Complex plays essential roles for Golgi function, vesicle trafficking and glycosylation. Mutations in the genes encoding human COG1, COG4-COG8 have been associated with congenital disorders of glycosylation (CDG). Deletions of human COG7 are associated with a rare multisystemic congenital disorder of glycosylation causing mortality within the first year of life. I show that, similar to Drosophila Cog5, Cog7 controls furrow ingression during cytokinesis. Importantly, Cog7 is required to localize the small GTPase Rab11 and the phosphatidylinositol transfer protein (PITP) Giotto (Gio) to the cleavage site of spermatocytes. In addition Gio coimmunoprecipitates with both Cog7 and Rab11 in Drosophila testes suggesting that these proteins may interact in male germ cells.