Glycogen synthase kinase 3beta and the regulation of axon growth

One of the earliest hallmarks that distinguish growing axons from dendrites is their growth rate; axons grow faster than dendrites. In vertebrates, where axons are required to grow for considerable distances, particularly in the peripheral nervous system, a fast axon growth rate is a requisite property. In neurons that respond to the neurotrophin growth factor/nerve growth factor with increased axon growth rates, two distinct intracellular signalling pathways are recruited: the MAPK (mitogen-activated protein kinase) pathway and the phosphatidylinositol-3 kinase pathway. The activation of either pathway leads to changes in microtubule dynamics within growing axons and growth cones and these underlie fast axon growth rates. Microtubule dynamics is regulated by microtubule-associated proteins and in the MAPK pathway this function is subserved by microtubule-associated protein 1B, whereas in the phosphatidylinositol-3 kinase pathway, adenomatous polyposis coli is the regulating microtubule-associated protein.