Figure 4.

General summary model of the regulation of the axonal cytoskeleton during branching. Branch inducing signals activate multiple pathways that independently regulate the actin filament and microtubule cytoskeleton. The ensuing cytoskeletal dynamics promote branching by increasing actin filament dependent protrusive activity and microtubule tip polymerization or transport into protrusions. Molecules that coordinate the actin filament and microtubule cytoskeleton, in turn serve to promote interactions between the cytoskeletal elements. It remains to be determined if and by which signaling pathways cytoskeletal coordinators may be under regulation by branch inducing signals. The formation of a branch requires the formation of protrusive structures along the axon through the regulation of actin filaments, and the targeting and retention of microtubules in these protrusions. The means through which these ends are accomplished, at the molecular level, are likely diverse relying on different signaling pathways and effectors, as discussed in the concluding statement.