Fig. 4. SCAR RNAi in S2R+ cells inhibits lamellipodial protrusion. (A) Morphometry. Projected area (left) and P/A1/2 cell shape index (right) of control (gray bars, n=24) and dsSCAR-treated for 4 days (black bars, n=26) S2R+ cells. Higher values of the index correspond to more irregular cell shape (see text for details). (B,C). Kinetics of lamellipodial protrusion on day 3 (B) and day 4 (C) of SCAR RNAi. Time series of enlarged boxed regions are shown on the right. Time in sec. (B) Cell is able to form lamellipodia, but protrusion is not coordinated along the edge. Formation of individual protuberances is indicated by arrowheads. (C) Cell is not able to form lamellipodia; it forms long narrow curved processes, which express dynamics at their tips and along their length (arrowheads). (D,E). Structure of actin cytoskeleton on day 3 (D) and day 4 (E) of SCAR RNAi (EM). (D) Lamellipodia-like protrusions contain very sparse dendritic actin filament network. (E) Long processes contain branched filament network, but not bundles of long filaments. Bars, 10 µm (B,C) and 0.2 µm (D,E).