Spatial control of F-actin dynamics during pupal eye morphogenesis. Steven J. DelSignore, Victor Hatini. Cell, Molecular & Developmental Biol, Tufts Univ Sackler Sch Biomed Sci, Boston, MA.

   Coordinated cell shape change drives the morphogenesis of many epithelial tissues during organ development. These precise patterns of shape change require the dynamic regulation of adhesion between cells, as changes in adhesion can promote cell shape change by causing the expansion or contraction of particular cell borders. The strength of adhesion depends on the degree of association between cell junctions and the underlying F-actin cytoskeleton. This interaction is enhanced by the activity of the small GTPase Rac1, which itself is recruited to junctions in part by phosphatidylinositol 3-kinase (Pi3k). Though the role of Rac1 at junctions has been clearly demonstrated in vitro, it remains unclear whether Rac1 regulates adhesion differentially between expanding and contracting cell borders to promote cell shape change in vivo. We examined the effect of Rac1 on actin dynamics and cell shape change in the developing drosophila eye. The drosophila compound eye is composed of ~800 light sensing units called ommatidia, each of which are surrounded by pigment epithelial cells. During development, pigment cells undergo elaborate shape changes to form a hexagonal that surrounds each ommatidium. To determine how F-actin dynamics contribute to these cell shape changes, we characterized F-actin dynamics by live imaging of the F-actin binding peptide lifeact::ruby, and compared wild type dynamics to experimental eyes with altered Rac1 signaling. Further, we performed an RNAi-based screen to identify novel regulators of F-actin dynamics during morphogenesis. Together, these studies suggest mechanisms by which F-actin dynamics and adhesion are regulated spatially and temporally to control cell shape change during morphogenesis.