Microtubule-associated proteins, phosphorylation gradients, and the establishment of neuronal polarity

Axonogenesis is the earliest step in acquisition of neuronal polarity. The subcellular mechanisms underlying this pivotal event are unknown. Because of the abundant presence and functional necessity of microtubule-associated proteins in growing neurites, a large effort has been directed at characterizing their role in establishment and maintenance of neuronal polarity. One unsolved puzzle is how MAPs, most of which are unpolarized in early stages of development, can locally influence microdifferentiation of axons and dendrites. In this review, we discuss recent evidence suggesting that locally controlled phosphorylation of microtubule-associated proteins tau and MAP1B may play a role in establishment of polarity and early axonal outgrowth.