Axonal protein synthesis and transport

Recent evidence has challenged our ideas about the nature of axonal protein synthesis and transport. Previous metabolic labeling evidence supported th e idea that all axonal proteins were synthesized in the cell body and then transported as formed cytoplasmic structures into the axon. Recent evidence suggests that neither the synthesis nor the transport of axonal proteins i s that simple. Though most axonal proteins do appear to be synthesized in t he neuronal cell body, a small amount of protein appears to be synthesized intra-axonally in some axons. Though small in amount, intra-axonal protein synthesis may be important functionally in some axons. Recent experiments h ave also begun to identify the presence of a rich array of transport motors in axons, including many members of the kinesin, dynein and myosin familie s. Progress is being made in identifying which cargoes are being transporte d by which of these motors. Finally, recent experiments have addressed an o ld question about whether axoplasmic proteins are transported as filamentou s polymers or as soluble components in axons. The answer is that both mecha nism can be used in axons. For example, neurofilament protein can move in i ts particulate or polymeric state, while tubulin can move in its soluble or unpolymerized state.