Intercellular Protein Equilibration through Somatic Ring Canals. Peter McLean. Genetics, Yale School of Medicine, New Haven, CT.

   Ring canals are the stabilized remnants of arrested cleavage furrows, and provide direct cytoplasmic connections between sibling cells. Ring canals connecting germline cells are known for their participation in Drosophila oogenesis, but little is known about their role in the several somatic tissues in which they are also found. In this study we use the ovarian follicle cells to investigate the impact of somatic ring canals on protein movement between cells and across an epithelium. Here, we expand upon our previously reported results of photoactivatable GFP (PAGFP) and computational modeling that show intercellular protein movement to be robust, limited to syncytial groups that vary in size, and driven by passive diffusion. Using cells that express mosaic GFP, we provide evidence by Fluorescence Loss in Photobleaching (FLIP) and Fluorescent In Situ Hybridization (FISH) that ring canals permit equilibration of protein between cells with highly disparate levels of transcription. We also use a novel combination of markers to evaluate the extent and impact of protein movement relative to mitotic clones in follicle cells and wing imaginal discs. We provide evidence of robust intercellular exchange of GFP between the two lineages of the mitotic clone. We conclude that, depending on the experimental setup and proteins of interest, intercellular protein movement may alter the interpretation of clonal data in follicle cells. In sum, our results provide the first evidence for a role of intercellular bridges outside of the germline, a major function of which is to mediate equilibration of protein across an epithelium of transcriptionally mosaic cells.