Profilin and the Abl tyrosine kinase are required for motor axon outgrowthin the Drosophila embryo

The ability of neuronal growth cones to be guided by extracellular cues req uires intimate communication between signal transduction systems and the dy namic actin-based cytoskeleton at the leading edge. Profilin, a small, acti n-binding protein, has been proposed to be a regulator of the cell motility machinery at leading edge membranes. However, its requirement in the devel oping nervous system has been unknown. Profilin associates with members of the Enabled family of proteins, suggesting that Profilin might link Abl fun ction to the cytoskeleton. Here, genetic analysis in Drosophila is used to demonstrate that mutations in Profilin (chickadee) and Abl (abl) display an identical growth cone arrest phenotype for axons of intersegmental nerve b (ISNb). Moreover, the phenotype of a double mutant suggests that these com ponents function together to control axonal outgrowth.