The role of the cytoskeleton in the morphological changes occurring during neuronal differentiation

Development of neurons from neuroblasts involves the extension of cytoplasmic processes (neurites) that mature into axons and dendrites in response to distinct extracellular signals. Changes in the cytoskeleton are crucial for neurite outgrowth and maturation. The initial sprouting of neurites requires rearrangements of actin microfilaments which are possibly under the control of proteins belonging to the Rho subfamily of GTPases. Little is known about the extracellular stimuli which regulate the activity of these GTPases in developing neurons. Likewise, the molecular mechanisms by which actin microfilament dynamics and organization are modified after the activation of Rho subfamily GTPases are not yet clear. The consolidation and maturation of growing neurites that become axons and dendrites requires the participation of other cytoskeletal elements, particularly microtubules. The expression and phosphorylation of specific microtubule-associated proteins may be important for axon and dendrite development. There is some information about the protein kinases and phosphatases that act on microtubule-associated proteins. However, much less is known about the signal transduction pathways that regulated microtubule-associated protein expression and phosphorylation in response to distinct extracellular signals.