Dynamic microtubules explore the peripheral (P) growth cone domain using F actin bundles as polymerization guides 1, 2. Microtubule dynamics are necessary for growth cone guidance 3, 4, 5, 6; however, mechanisms of microtubule reorganization during growth cone turning 7, 8, 9 are not well understood. Here, we address these issues by analyzing growth cone steering events in vitro, evoked by beads derivatized with the Ig superfamily cell adhesion protein apCAM. Pharmacological inhibition of microtubule assembly with low doses of taxol or vinblastine resulted in rapid clearance of microtubules from the P domain with little effect on central (C) axonal microtubules or actin-based motility. Early during target interactions, we detected F actin assembly and activated Src, but few microtubules, at apCAM bead binding sites. The majority of microtubules extended toward bead targets after F actin flow attenuation occurred. Microtubule extension during growth cone steering responses was strongly suppressed by dampening microtubule dynamics with low doses of taxol or vinblastine. These treatments also inhibited growth cone turning responses, as well as focal actin assembly and accumulation of active Src at bead binding sites. These results suggest that dynamic microtubules carry signals involved in regulating Src-dependent apCAM adhesion complexes involved in growth cone steering.
