PERSPECTIVES

receptor, and cytoskeletal components (actin microfilaments and a nonmuscle myosin, together called actomyosin). In response to Wnt5a, all of these proteins become polarized in overlapping bands within the trailing edge of migrating cells (see the figure). Polarized bands of ac-tomyosin contract to lift the trail-ing edge and, together with cell process extensions at the leading edge, promote migration toward a chemokine source. Multiple pulses of these transient polariza-tions occur within single cells over time. In exploring the signaling pathway that mediates this Wnt5a response, Witze et al. dis-covered that actin microfilaments and the cel