Figure 7.
Laminin increases Rac1 activity. A–F, Growth cones colabeled for active Rac1 using GST–PBD (A–C; see Materials and Methods) and filamentous actin using fluorescent phalloidin (D–F). Growth cones that were stimulated with 25 μg/ml LN for 10 min before fixation (B) appear brighter than unstimulated controls (A), indicating increased Rac1 activity. Arrows point to apparent local areas of active Rac1 at the growth cone periphery. Growth cones pretreated with β1-integrin function-blocking antibody (C) appear similar to unstimulated control growth cones. G, Quantification of GST–PBD binding. The average fluorescence intensity was measured within the entire growth cone using MetaMorph software. The addition of LN (n = 34) significantly elevated Rac1 activity compared with control (n = 40); this increase was blocked by pretreatment with β1-integrin function-blocking antibody (n = 38). Scale bar, 5 μm. **p < 0.001. Error bars indicate SEM. ab, Antibody.