Dynamics of the Dictyostelium Arp2/3 complex in endocytosis, cytokinesis, and chemotaxis

The Arp2/3 complex is a ubiquitous and important regulator of the actin cyt oskeleton. Here we identify this complex from Dictyostelium and investigate its dynamics in live cells. The predicted sequences of the subunits show a strong homology to the members of the mammalian complex, with the larger s ubunits generally better conserved than the smaller ones. In the highly mot ile cells of Dictyostelium, the Arp2/3 complex is rapidly re-distributed to the cytoskeleton in response to external stimuli. Fusions of Arp3 and p41- Arc with GFP reveal that in phagocytosis, macropinocytosis, and chemotaxis the complex is recruited within seconds to sites where actin polymerization is induced. In contrast, there is little or no localization to the cleavag e furrow during cytokinesis. Rather the Arp2/3 complex is enriched in ruffl es at the polar regions of mitotic cells, which suggests a role in actin po lymerization in these ruffles. (C) 2001 Wiley-Liss, Inc.