Fig. 8. Model for polarization and propagation of directional locomotion. Discoid, non polarized cytoplast is "pushed" at its bottom which results in accumulation of actin filaments (long blue lines) and clusters of myosin filaments (short red lines) into a bundle along the deformed edge. Protrusion at deformed edge is inhibited, but proceeds at opposite edge (protrusion), while relative accumulation of myosin and filament alignment at the deformed edge favors further retraction, reinforcing functional asymmetry. Protrusion and retraction occur simultaneously at opposite edges in the steady state. Turnover of myosin II results in formation of new myosin clusters in the newly protruded lamellum permitting subsequent contraction in the rear (see text for detailed model).
