The role of the Arp2/3 complex in actin dynamics during oogenesis. A.M. Hudson , L. Cooley. Dept Genetics, Yale Univ Sch of Medicine, New Haven, CT 06520.

   The Arp2/3 complex is a seven-protein complex that has been shown to dramatically increase the slow spontaneous rate of actin filament nucleation, and is thus presumed to be important for dynamic actin rearrangements in vivo. We have isolated and characterized lethal mutations in two components of the Arp2/3 complex: Dsop2, the homolog of the p40-Arc subunit, and Arp3 one of actin related proteins. Our initial analysis of these mutations has focused on oogenesis, where dynamic changes in actin cytoskeleton are required at several stages. Disruption of Arp2/3 complex function by loss of either Dsop2 or Arp3 in the ovary results in a failure of cytoplasm transport from the nurse cells to the oocyte. This failure results specifically from a defect in the actin rich ring canals that serve to interconnect the 15 nurse cells with the oocyte. In contrast, the parallel actin bundles that form in the nurse cell cytoplasm at stage 10B of oogenesis, as well as the parallel actin bundles that are required for bristle extension, are able to form, providing evidence that the Arp2/3 complex is required for a specific subset of dynamic actin rearrangements. In an effort to determine how the Arp2/3 complex participates in ring canal development, we have generated several reagents to determine the subcellular distribution of the Arp2/3 complex, including antibodies against Drosophila Arp2/3 components, as well as GFP fusions to both Dsop2 and Arp3. Preliminary results show an enrichment of Arp2/3 components on ring canals. In addition, we have also created a GFP-Actin transgene that is expressed in the germline, and we are using this transgene to compare wild-type ring canal actin dynamics with those in Arp2/3 mutants.