Figure 6.

Morphometric analysis of the distribution of nucleation sites and filament density at the leading edge. (A) Quantitation of nucleation activity at the leading edge was done on negatively stained samples by analyzing the distribution of the gold particles reflecting biotin-labeled actin incorporation, using a macro designed for NIH Image, as described in Fig. 5. All the counts were performed blind: (squares) unstimulated cells, nonlamellipod-like edges (see Fig. 5 A); (open circles) leading edges in unstimulated cells (see Fig. 5 B); (triangles) EGF 30 s; (diamonds) EGF 1 min (see Fig. 5 C); (stars) EGF 3 min; and (closed circles) EGF 5 min. The data shown are from one representative experiment using 5–8 cells per time point. Additional examples of the distribution of barbed ends at the leading edge are shown in Figs. 9 and 10. (B) Quantitation of filament density was performed on the same set of negatively stained samples as in A, with a slight adaptation of the method (see Materials and Methods). The legend is the same as in A, except that (squares) unstimulated cells in regions with no typical leading edge are not shown.