Polarization of the Drosophila Oocyte

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0091254CohenVirtually all cells are polarized and need to be in order to carry out their programmed functions. The mechanisms by which cells acquire, maintain and elaborate polarity have been well conserved through evolution. In general, cell polarization begins at the cell periphery when an asymmetric cue induces local remodeling of the actin fibers, generating an "actin patch." Members of the Rho family of GTPases are recruited to these patches and activate secondary signaling molecules that propagate the cellular response by reorganizing the actin and microtubule cytoskeletons, and polarizing the plasma membrane and intracellular membrane trafficking pathways. There is a growing body of evidence that feedback loops are built into this basic pathway to reinforce and amplify the response. For example, disruption of Rho activity in epithelial cells causes a loss of cell-cell contacts, implicating these GTPases in the maintenance of the same adhesion complexes that recruit and activate them in the first place. The recent discovery that Rab11, a conserved member of the membrane recycling pathway, is required for microtubule organization and RNA localization in Drosophila oocytes would appear to reveal another such feedback loop. Specifically, it is proposed that Rab11, in response to an asymmetric cue and Rho CTPase activation, polarizes the plasma membrane, thereby enhancing reception of the asymmetric cue, Rho GTPase activation and "downstream" polarization events, such as microtubule organization and RNA localization. Here, a "candidate gene" approach is described that seeks to identify markers of Drosophila oocyte membrane polarity. In particular, a number of adhesion molecules and other proteins that define polarity of other plasma membrance systems will be examined immunocytochemically for asymmetric distribution along the oocyte's plasma me