Dia- and Rok-dependent enrichment of capping proteins in a cortical region

Rho signaling with its major targets the formin Dia, Rho kinase (Rok) and non-muscle myosin II (MyoII, encoded by zip in flies) control turnover, amount and contractility of actomyosin. Much less investigated has been a potential function for the distribution of F-actin plus and minus ends. In syncytial Drosophila embryos, Rho1 signaling is high between actin caps, i.e. the cortical intercap region. Capping protein binds to free plus ends of F-actin to prevent elongation of the filament. Capping protein has served as a marker to visualize the distribution of F-actin plus ends in cells and in vitro. In the present study, we probed the distribution of plus ends with capping protein in syncytial Drosophila embryos. We found that capping proteins are specifically enriched in the intercap region similar to Dia and MyoII but distinct from overall F-actin. The intercap enrichment of Capping protein was impaired in dia mutants and embryos, in which Rok and MyoII activation was inhibited. Our observations reveal that Dia and Rok-MyoII control Capping protein enrichment and support a model that Dia and Rok-MyoII control the organization of cortical actin cytoskeleton downstream of Rho1 signaling.