Fig. 5.

Actin polymerization in thick bundles visualized by spinning-disk confocal microscopy. In myosin II-null cells, GFP-actin is expressed for incorporation into filamentous actin (green). The membranes of intracellular vesicles, primarily of the contractile vacuole complex, are labeled by FM4-64 (red). (A) A bundle that extends from its origin (open arrowhead) to the left and forms a kink when it hits the membrane (closed arrowhead). As in Fig. 4A, depolymerization starts at the rear of the filament (7-sec frame). (B) An actin bundle that gives rise to a filopod-like extension by applying force onto the cell border. (C) Velocities of tip progression in thick bundles labeled by the incorporation of GFP-actin. Data are from 85 measurements on 16 actin bundles. (Scale bars: 5 μm.)