Figure 1.

Actin filament dynamics and growth cones.

(A) Schematic of actin filament nucleation and turnover. Actin filaments are polarized polymers consisting of a barbed end and a pointed end (top). The barbed end exhibits higher rates of polymerization, while the pointed end has higher rates of depolymerization. Both nucleation and polymerization at the barbed end of filaments are promoted by adenosine triphosphate (ATP) loaded actin subunits. During filament turnover, adenosine diphosphate (ADP) loaded actin subunits are depolymerized from the pointed end of the filament. The ADP is then exchanged with ATP in the cytosol thereby restoring the actin subunit to a nucleation/polymerization competent state and can be reused in further cycles of nucleation or polymerization. Created with BioRender.com. (B) Examples of the growth cones (GC) and axons of embryonic chicken sensory neurons in vitro labeled to reveal actin filaments (red) and microtubules (green). Note that actin filaments exhibit a higher density at the growth cones than along the axon shaft. Unpublished data from our laboratory. Scale bar: 10 mm.