Fig. 2. The LD4 motif of paxillin regulates cell protrusion and retraction. CHO-K1 cells stably transfected with (A) wild-type paxillin or (B) a mutant of paxillin that lacks the LD4 motif (LD4) were spread on 10 µg/ml fibronectin for 2 hours in the presence of serum. Cells were fixed and stained for F-actin (red) and paxillin (green). Deletion of the LD4 domain of paxillin results in extensive peripheral protrusive activity (arrows) and defective tail retraction (arrowhead). It is also of note that the protrusions observed in cells that express paxillinLD4 contain numerous dot-like paxillin-rich focal complexes at their periphery, which are less prevalent in cells that express wild-type paxillin. Scale bars: 20 µm.