Investigating the Predicted Enzymatic Activity of Asteroid in Drosophila Oogenesis and DNA Repair
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The intricate process by which gametes are formed from the germline stem cells is a fundamental question in biology. In Drosophila, oogenesis, begins by asymmetric division of the germline stem cells, and ultimately produces a cyst of 16 cells surrounded by a layer of somatic cells. One of these 16 cells is selected as the oocyte, the future egg, while the remaining become supporting cells. A genetic screen in Drosophila identified mutations in several evolutionarily conserved genes that result in a failure of oocyte fate determination, leading to loss of mature eggs and fertility. Strikingly, when the germline cells are mutant for asteroid (ast), one of the genes identified in this screen, the resulting cysts contain no oocyte. Further characterization of asteroid mutants revealed a persistence of double-stranded DNA breaks (DSBs) during meiosis. Interestingly, the protein encoded by ast and its human ortholog (ASTE1) both contain XPG domains, suggesting they are nucleases involved in DNA repair. Additionally, ASTE1 is mutated in a subset of patients with colorectal cancers, although its molecular function is unknown. To study the role of Asteroid in vivo and in vitro, biochemical and genetic experiments are currently underway. These studies aim to address the necessity of Ast’s predicted nuclease domain during Drosophila oogenesis, as well as to examine the enzymatic activity of Asteroid and ASTE1 in vitro. Further investigation of asteroid and ASTE1 will shed much needed light on oocyte fate determination, as well as their roles in DNA repair, and possibly cancer.