RhoGAP68F regulates endocytic recycling to facilitate epithelial flattening and tissue elongation. Beatriz Hernandez de Madrid, Lina Greenberg, Victor Hatini. Anatomy and Cell Biology, Tufts University, Boston, MA.

   Epithelial elongation is a conserved morphogenetic process that shapes the morphology of the primary body axis as well as tissue and organs. Epithelial elongation requires coordinated assembly and disassembly of cell-cell junctions but the mechanisms involved are incompletely understood. During metamorphosis the leg disc dramatically elongates from a short and wide disc to a long and narrow tube providing a model to study tissue elongation. Leg elongation is mediated by coordinated changes in cell shape, cell-cell contacts, and the flattening of the epithelium from pseudostratified to simple. In an RNAi screen designed to uncover new regulators of tissue elongation, we had selected the Rho family regulator RhoGAP68F for further analysis. We find that RhoGAP68F is required to promote epithelial flattening. Functional analysis in vivo revealed that overexpressed mCherry::RhoGAP68F strongly colocalized with Rab4 recycling endosomes, caused their dramatic enlargement and clustering, and reduced their normal accumulation near the apical surface. Analysis in Schneider 2 cells revealed that RhoGAP68F reduced the speed and displacement of the Rab4 endosomes. The Rab4 endosomes colocalized with the septate junction (SJ) protein FascilinIII (FasIII) and both Rab4 and FasIII were required for leg elongation. Our findings suggest that RhoGAP68F inhibits the recycling of SJs back to the plasma membrane to diminish lateral cell-cell contact in order to facilitate epithelial flattening. Our current studies are designed to test the role of RhoGAP68F in trafficking of SJs components to the plasma membrane and the remodeling of SJs.