Developmental axon regrowth and primary neuron sprouting utilize distinct actin elongation factors

Intrinsic neurite growth potential is a key determinant of neuronal regeneration efficiency following injury. The stereotypical remodeling of Drosophila y-neurons includes developmental regrowth of pruned axons to form adult specific connections, thereby offering a unique system to uncover growth potential regulators. Motivated by the dynamic expression in remodeling y-neurons, we focus here on the role of actin elongation factors as potential regulators of developmental axon regrowth. We found that regrowth in vivo requires the actin elongation factors Ena and profilin, but not the formins that are expressed in y-neurons. In contrast, primary y-neuron sprouting in vitro requires profilin and the formin DAAM, but not Ena. Furthermore, we demonstrate that DAAM can compensate for the loss of Ena in vivo. Similarly, DAAM mutants express invariably high levels of Ena in vitro. Thus, we show that different linear actin elongation factors function in distinct contexts even within the same cell type and that they can partially compensate for each other.