FIGURE 1.

A schematic cross section of a stereocilia, with indication of the transport and actin regulation processes: red filaments represent the treadmilling actin (black arrows show the retrograde flow with velocity v_a), with actin monomers shown diffusing from the depolymerizing ends at the base to the tip. Proteins that regulate the actin dynamics are shown to bind to either the treadmilling of actin filaments (dashed box I), or to the downward moving myosin-VI (green), or to the upward moving myosins (purple; myosin-XV, myosin-III, etc.) (dashed box III). The purple arrows show the constant velocity v_m of the myosin motion up and the green arrows show the constant velocity v_m down along the stereocilia (dashed box II). Proteins that inhibit the actin polymerization (IP) are shown in orange, while proteins that promote the actin polymerization (AP) are shown in light blue. Disassembly factors (black shapes) depolymerize the actin filaments at the stereocilia base and are localized there by the actin treadmilling or by myosin-VI (dashed box IV). The stereocilia has a narrow base of radius R_base, and assumes the shape of a cylinder with radius R_tip higher up. All the transport processes (diffusion and myosin motion) are confined to the narrow space separating between the actin bundle and the membrane (of thickness δ), along the outer contour (coordinate s, dashed box V).