Differential cytoskeletal changes during growth cone collapse in response to hSema III and thrombin

Growth cones are known as the site of action of many factors that influence neurite growth behavior. To assess how different collapsing agents influen ce the growth cone cytoskeleton, we used recombinant human Semaphorin III ( hSema III) and the serine protease thrombin. Embryonic chick dorsal root ga nglion neurons showed a dramatic depolymerization of actin filaments within 5 min upon hSema III exposure and virtually no influence on microtubules ( MT). Only at rater time points (20-30 min) was the polymerization/depolymer ization rate of MT significantly affected. Thrombin induced a morphological ly and kinetically similar growth cone collapse. Moreover, thrombin induced an early and selective depolymerization of dynamic MT, accompanied by the formation of loops of stable MT bundles. Selective changes in the phosphory lation pattern of tau were associated with microtubule assembly in thrombin -induced responses. Our data provide evidence that different signal transdu ction pathways lead to distinct changes of the growth cone cytoskeleton.