FAK^−/− Pyk2 shRNA MEFs exhibit tail-retraction motility defects. (A) FAK-reconstituted DP3 MEFs were plated on 1 μg/ml FN and monitored for random cell motility in 10% FBS over the indicated time (images obtained from Video1). Cells show normal protrusive activity at the leading edge and coordinated tail retraction (arrows) as the cell moves forward. Bar, 30 μm. (B) FAK^−/− Pyk2 shRNA MEFs on 1 μg/ml FN exhibit membrane-ruffling activity in the presence of 10% FBS (images obtained from Video 3). Efficient motility does not occur as cells exhibit defects in tail-associated FA release (arrows). A cell-snapping phenotype is common with pieces of cell material left behind. Bar, 30 μm.