Abstract
The seemingly simple structure of the actin filament belies the elaborate signaling pathways that regulate its assembly and disassembly in eukaryotic cells. In retrospect, this signaling complexity should not be surprising. Actin regulates many dynamic cellular processes, including protein and organelle trafficking, establishment of cell polarity, directional migration, cellular traction, and the efficiency of endocytosis. Signaling events that coordinately control actin turnover during these processes must display a high degree of sophistication. Emerging data on an important regulator of actin dynamics, the actin-related protein 2 and 3 (Arp2/3) complex, suggest a model of how this may occur.