Fig. 1.

(A) Model of actin ultrastructure in the lamellipodium. From the network of cortical actin filaments (black), dendritic nucleation and polymerization pushes the cell membrane (blue) forward. Filaments are debranched and disassembled at the rear of the protruding lamellipodium. Regions of assembly (green plus signs) and disassembly (red minus signs) are shown. (B) Fluorescence light micrograph of a migrating Xenopus laevis fibroblast that was fixed and stained with Rhodamine-phalloidin. Reproduced with permission from Svitkina and Borisy [Svitkina and Borisy 1999]. A small region of the lamellipodium represented by the cartoon in A is indicated (white box).