Sticky fingers for migration

Sticky fingers for migration R oaming cells send out sticky fi ngers to probe for good attachment points, say Catherine Galbraith, Kenneth Yamada, and James Galbraith (NIH, Bethesda, MD). The fi ngers’ sideways movements give cells a wider fi eld of vision than do forward and reverse movements alone. These sideways movements were picked up by the authors as ripples in the plasma membrane at the very front of a migrating fi broblast. The ripples were made by polymerizing actin fi laments that elongated nearly parallel to the lamellipodial leading edge. Their quick polymerization moved the ripples several times faster than lamellipodia can extend forward. The tips of the actin fi laments at the ripple crests were attached to ready-to-bind adhesion receptors. Although not yet bound to the matrix, these β1 integrins were in a conformation that readily binds to fi bronectin. Actin polymerization in the unique environment of the extreme leading edge, where adhesions are lacking, seems somehow to drive their active conformation; decreasing polymerization reduced the number of activated receptors. Similar activated integrins were found by the group at the tips of long searching fi lopodia at the front of neuronal growth cones. “It’s easiest to picture sticky fi ngers in the growth cones,” says Catherine Galbraith. “They’re how cells feel along, looking for good adhesion sites.” These sites have the proper stiffness and the right matrix ligands to initiate formation of adhesion foci.