Cortactin labels the protruding edges of spreading MEFs and is coincident with Arp2/3 complex. A. MEFs were spread for 60 minutes on fibronectin. Scale bar 10 μm. B. Enlargement of boxed area in A. Merge is of cortactin (4F11 antibody) and Arp2/3 complex (antibody to p34-Arc sub-unit). Scale bar 10 μm. C. Intensity of cortactin (red line) and Arp2/3 complex (green line) signals relative to respective maximum (set at 1) values along the lengths (arbitrary units) of boxed filopodia in B.