How do neuronal proteins know where they are going? . . . Speculations on the role of molecular address markers.

The neuroscientist often divides the cellular world into neuronal and nonneuronal cells, setting the stage for emphasizing differences rather than similarities between cell types. This review focuses on a common theme in cell biology: the sorting of newly-synthesized membrane proteins, their intracellular transport, and their delivery to distinct domains of the cell surface. At the subcellular level, membrane proteins in neurons pass through the cell body and enter the axon by a pathway reminiscent of that utilized in other cell types. At the molecular level, little is known of how sorting and delivery are directed in neurons, although details of such recognition mechanisms are emerging for many specific proteins in prokaryotic and eukaryotic cells. Analogies are drawn from these systems to propose how neuronal proteins destined for regions of axolemma and axon terminals are sorted from proteins destined for endomembranes, somal organelles, somal plasma membrane and dendrites, and delivered, via fast axonal transport, to their correct membrane domains.