Characterization of the Bristle mutant in Drosophila melanogaster. Pooneh Vaziri, Eduardo Gonzalez-Niņo, Jennifer Curtiss. New Mexico State University , Las Cruces, NM.

   The regulation of cell adhesion plays a crucial role in the formation and maintenance of tissue during development of multicellular organisms. The Rap1 small GTPase regulates adhesion between cells and affects localization of adherens junctions. Small GTPases are molecular switches that are active when bound to GTP and inactive when bound to GDP. GEFs promote the active state of the GTPase and GAPs promote the inactive form. To further investigate the mechanisms by which Rap1 regulates cell adhesion, we performed a screen to identify mutants that modify a Rap1 mutant eye phenotype in Drosophila melanogaster. One of the mutants that we identified is the Bristle (Bl) mutant, which enhances the Rap1 loss of function eye phenotype. In the Bl mutant the bristles that cover all parts of the fly are shorter and thicker than in normal flies. Since it was not previously known which gene is affected by the Bl mutation, we performed complementation tests with mutants that lie close to the Bl locus. Mutations in the skywalker (sky) gene fail to complement the Bl mutation, suggesting that Bl is an allele of sky. The sky gene encodes a GAP that is known to inactivate another class of small GTPases: the Rabs. Rab proteins are important for formation and localization of vesicles in specific trafficking pathways. Also it has been demonstrated that Rab35, which is a previously known target of Sky, is involved in actin bundling during the formation of bristle in D. melanogaster. We overexpressed the sky gene in bristle precursors, and found that the resulting adult bristles have defects similar to those in the Bl mutant, suggesting that the Bl mutation results in the overexpression of the sky gene. To confirm that Bl is an allele of sky, we are performing quantitative PCR to determine whether expression of the sky gene is altered in Bl flies compared to wild-type flies, and we are sequencing sky genomic DNA from Bl flies to determine the nature of the mutation. In addition, we are performing genetic experiments to elucidate the relationship between Rap1 and sky.