Figure 2.

Axonal actin filament patch formation and dynamics. (A) Example of actin patch formation (yellow arrow at 6 sec), elaboration (6–18 sec) and dissipation (30–42 sec) as imaged along the axon of an embryonic sensory neuron expressing eYFP-β-actin. (B) Possible actin filament nucleators involved in the initiation of actin patches. The specific nucleators required for patch initiation remains to be determined, as reflected by the (?). (C) The Arp2/3 complex is required for the detection and elaboration of axonal actin filament patches. The inset shows an example of the complex network of actin filaments in axonal actin patches, as detected using platinum replica electron microscopy (from a collaboration with Dr. T. Svitkina, University of Pennsylvania). PI3K activity drives the Rac1 GTPase that in turn activates the Arp2/3 complex through WAVE1. Cortactin serves to stabilize Arp2/3 mediated filament branches and positively regulates the elaboration of patches.