Fig. 3. Distribution of Rac 1. (A,B) Localization of Rac 1 in a growth cone cultured on a polyamine substrate. There is an extensive ribbed network of F-actin (A). Rac 1 in the same growth cone does not substantially localize to this peripheral network, but some colocalization is seen in the C region of the growth cone (B). Bar, 10 µm. (C,D) On a laminin substrate, Rac 1 is often colocalized with F-actin at the leading edge of the growth cone (arrows). Bar, 10 µm. (E) Detail of a part of a growth cone on a polyamine substrate that was acutely exposed to laminin. At the site of outgrowth of a streamlined growth cone, microtubules advance into a filopodium and colocalize with Rac 1 (arrow). A filopodium lacking microtubules does not contain Rac 1 (arrowhead). Bar, 2 µm.