Cell locomotion requires coordinated cycles of protrusion of the leading edge of the cell, formation of new matrix adhesions, and retraction of the trailing edge. Matrix adhesions, which form first as focal complexes (FXs) and then transform into focal adhesions (FAs), provide anchors for the contractile machinery of the cell. By analysing endothelial cells migrating into a 500 μm wide scratch in a confluent monolayer of cells (an in vitro `wound'), Benjamin Geiger and colleagues provide a detailed description of the early stages of FA development (see ). They report that short-lived FXs, which form behind the leading lamellae of motile cells, accumulate FA proteins (for example, β3-integrin and paxillin) in an ordered manner that depends on their age. The final composition of the FXs is distinct from FAs, however, in that they lack zyxin, and the researchers show that the transition from paxillin-rich FXs to zyxin-containing FAs occurs only when the leading edge of the cell stops advancing or retracts.
