Fig. 1. The branched actin networks found in fibroblast lamellipodia (A) and actin bundles in a bristle of Drosophila melanogaster (B) [Adapted with permission (Hudson and Cooley, 2002; Svitkina and Borisy, 1999)] (bar, 0.1 µm); a schematic diagram showing branched (C) and unbranched (D) actin filaments. The Arp2/3 complex (green) crosslinks and stabilizes branched filaments, whereas tropomyosin (purple) stabilizes unbranched filaments.