Nascent Lamellipodia Emerge with Rough Edges and Rapidly Acquire a Smooth Morphology. A glass micropipette, acting as a barrier, was lowered into the path of movement of a migrating, coherent keratocyte overexpressing EGFP-VASP (an indicator of polymerizing actin). When the keratocyte reaches the barrier, the lamellipodium temporarily stops protruding forward, while EGFP-VASP becomes displaced from the edge of the region in contact with the barrier. When the micropipette barrier is removed (between 0:57 and 1:00), the leading edge of the lamellipodium immediately resumes protrusion and appears rough with several protruding microregions enriched in EGFP-VASP. Only 18 s after removal of the barrier, the keratocyte’s original shape and uniform EGFP-VASP localization at the leading edge are restored. Time ¼ min:s. Scale bar 25 micron. Corresponds to video S2 in PLos Biology 5:2035-2052, 2007.