Spatial control of actin polymerization during neutrophil chemotaxis

Neutrophils respond to chemotactic stimuli by increasing the nucleation and polymerization of actin filaments, but the location and regulation of thes e processes are not well understood. Here, using a permeabilized-cell assay , we show that chemotactic stimuli cause neutrophils to organize many discr ete sites of actin polymerization, the distribution of which is biased by e xternal chemotactic gradients. Furthermore, the Arp2/3 complex, which can n ucleate actin polymerization, dynamically redistributes to the region of li ving neutrophils that receives maximal chemotactic stimulation, and the lea st-extractable pool of the Arp2/3 complex colocalizes with sites of actin p olymerization. Our observations indicate that chemoattractant-stimulated ne utrophils may establish discrete foci of actin polymerization that are simi lar to those generated at the posterior surface of the intracellular bacter ium Listeria monocytogenes. We propose that asymmetrical establishment and/ or maintenance of sites of actin polymerization produces directional migrat ion of neutrophils in response to chemotactic gradients.