Figure 1.

Schematic of growth cone cytoplasmic and cytoskeletal organization. The C and P domains are separated by the T zone. The C domain contains a high density of stable microtubules (yellow) serving as structural support for axon elongation and substrates for fast axonal transport of organelles into the growth cone. The tips of microtubules extending beyond the T zone into the P domain are highly dynamic and continuously explore the actin-rich periphery via stochastic assembly and disassembly, using the F-actin bundles as polymerization guides. The P domain consists of alternating lamellipodia and filopodia regions, with highly polarized actin bundles in the filopodia (green), and more randomly oriented actin networks in the lamellipodia (gray). F-actin assembly along the leading edge of lamellipodia and in the tips of filopodia is balanced by myosin-driven retrograde actin flow. Transverse actin arcs (blue) undergoing Rho-dependent contractility are located in the T zone around the C domain. Also, in the T zone de novo actin assembly occurs in ruffling structures (red), also named intrapodia. Adapted from Schaefer et al. (12).