Fig. 6. Altered filopodial activity in the leading edges of 3 mutant cortical cells. E14 neuronal cells from wild-type or mutant cortices were electroporated with PH-Akt-EGFP (A,B) and time-lapse images of the growth cone ends of neuronal processes were recorded after 48 hours. PH-Akt-EGFP is targeted to active growth cones, thus enabling the evaluation of leading edge activity. In PH-Akt-EGFP transfected wild-type cells (A), filopodia emerge in large numbers from many spots along the leading edge (A; see activity in regions marked with asterisks) and appear to intensely sample the environment of the cell. By contrast, fewer filopodia emerge from the two adjacent leading edges (^{^}, ^*) of PH-Akt-EGFP transfected 3 integrin mutant cortical cells (B), and their ability to probe the cellular environment appear to have been retarded (compare activity in regions marked with asterisks in A and B). Re-expression of 3 integrin in 3 integrin-deficient cells rescued the deficits in filopodial activity (C; see active region marked with an asterisk). n=67 (wild type), n=70 (mutant and mutant + 3 integrin). Time elapsed since the beginning of observations is indicated in minutes. Scale bar: 20 µm. (Also see Movies 8-10 in the supplementary material.)