THE ROLE OF THE CYTOSKELETON IN THE MORPHOLOGICAL-CHANGES OCCURRING DURING NEURONAL DIFFERENTIATION

Development of neurons from neuroblasts involves the extension of cyto plasmic processes (neurites) that mature into axons and dendrites in r esponse to distinct extracellular signals. Changes in the cytoskeleton are crucial for neurite outgrowth and maturation. The initial sprouti ng of neurites requires rearrangements of actin microfilaments which a re possibly under the control of proteins belonging to the Rho subfami ly of GTPases. Little is known about the extracellular stimuli which r egulate the activity of these GTPases in developing neurons. Likewise, the molecular mechanisms by which actin microfilament dynamics and or ganization are modified after the activation of Rho subfamily GTPases are not yet clear. The consolidation and maturation of growing neurite s that become axons and dendrites requires the participation of other cytoskeletal elements, particularly microtubules. The expression and p hosphorylation of specific microtubule-associated proteins may be impo rtant for axon and dendrite development. There is some information abo ut the protein kinases and phosphatases that act on microtubule-associ ated proteins. However, much less is known about the signal transducti on pathways that regulated microtubule-associated protein expression a nd phosphorylation in response to distinct extracellular signals. (C) 1996 Academic Press Ltd