asteroid is required for oocyte determination in Drosophila. Julie A. Merkle, Trudi Schüpbach. Howard Hughes Medical Institute, Department of Molecular Biology, Princeton University, Princeton, NJ.

   A fundamental question in biology is how functional gametes are formed from the gerrmline stem cells. In many species, oogenesis establishes the molecular and developmental events necessary to promote fertility and embryonic development. How the oocyte establishes an identity and how that identity is maintained are processes that are still not well understood. In order to reveal new players involved in the control of these processes, we performed a mosaic screen on Chromosome 2L in Drosophila and isolated a set of 20 lethal mutations that display defects in oocyte specification and/or differentiation. In the majority of these mutants, clones produced 16 nurse cells and no oocyte. We are currently in the process of mapping these mutations and further characterizing the phenotypes. We mapped a mutation in one of these lines to asteroid (ast), a gene previously shown to interact with Star and Egfr in the Drosophila eye. The protein encoded by ast is conserved throughout metazoans and contains an XPG domain, suggesting a role for Ast in DNA repair. Future goals include further characterization of the ast mutant phenotype, as well as investigating its predicted nuclease activity, as to elucidate the mechanism by which Asteroid promotes oocyte specification and differentiation in Drosophila.