Rab8 is Required for the Regulation of Invagination of the Furrow Canal in Cellularization During Drosophila Embryogenesis. Lauren Mavor, J. Todd Blankenship. Biological Sciences, University of Denver, Denver, CO.

   Epithelial sheets create a boundary between the exterior and interior environments of organisms. The maintenance of adhesion within these sheets is critical to the function of the tissue and loss of this maintenance drives the metastasis of many epithelial cancers. In Drosophila, the epithelium is created via a process known as cellularization. Cellularization requires the coordinated invagination of plasma membrane to create an epithelial sheet 30m tall. In the presented work, we show that vesicular trafficking is necessary for this invagination process to occur. Using fixed and live-imaging in vivo, we have shown that Rab8, a late exocytic vesicle marker, localizes both to metaphase furrows during syncytial divisions prior to furrow ingression and to the Furrow Canal (FC) during cellularization. Prior to the onset of cellularization, Rab8 forms tubule-like projections, which mark future ingression furrows and precede F-actin, a cytoskeletal element known to play a vital role during this process. During cellularization, these same tubules follow the length of the FC and lead the basal-most portion of the FC. Knockdown of Rab8 via RNAi leads to a failure in formation of the FC and thus failure to initiate cellularization. Previous reports have shown that membrane trafficking via the recycling endosome and Golgi body are required to drive the cellularization process; however, in the presented work we show that Rab8 is both more dynamic and functions at an earlier stage of the ingression process than these two compartments. Thus we propose that polarized vesicular trafficking via late exocytic pathways is the primary pathway required for providing the membrane components necessary to drive the invagination of the FC and thus form the epithelial sheet of the Drosophila embryo.