Fig. 4. Bundled dynamic microtubules associate with F-actin during outgrowth in the presence of CD. (A) After treatment with 125 nM CD for 20 minutes, a growth cone on a polyamine substrate shows an almost complete loss of F-actin (green), with microtubules (red) filling the growth cone. Bar, 10 µm. (B-D) 25 minutes after the addition of laminin to such a growth cone, microtubules have bundled at peripheral sites where protrusions form and then develop into neurites. (B) Merged image of tyrosinated tubulin (green) and total tubulin (red) in a protrusion shows an enrichment of tyrosinated tubulin. Bar, 2 µm. (C) An F-actin focus (green) is intimately associated with an accumulation of microtubules (red). Bar, 2 µm. (D) All outgrowths show F-actin foci associated with bundling microtubules. Bar, 10 µm.