Protein trafficking mechanisms associated with neurite outgrowth and polarized sorting in neurons

Neuronal differentiation in vitro and in vivo involves coordinated changes in the cellular cytoskeleton and protein trafficking processes. I review he re recent progress in our understanding of the membrane trafficking aspects of neurite outgrowth of neurons in culture and selective microtubule-based polarized sorting in fully polarized neurons, focusing on the involvement of some key molecules. Early neurite outgrowth appears to involve the prote in trafficking machineries that are responsible for constitutive trans-Golg i network (TGN) to plasma membrane exocytosis, utilizing transport carrier generation mechanisms, SNARE proteins, Rab proteins and tethering mechanism s that are also found in non-neuronal cells. This vectorial TGN-plasma memb rane traffic is directed towards several neurites, but can be switch to con centrate on the growth of a single axon. In a mature neuron, polarized targ eting to the specific axonal and dendritic domains appears to involve selec tive microtubule-based mechanisms, utilizing motor proteins capable of dist inguishing microtubule tracks to different destinations. The apparent gaps in our knowledge of these related protein transport processes will be highl ighted.