Membrane Traffic in Neurons and Peptide-secreting Cells

Many epithelial cells are polarized with an apical plasma membrane dissimilar to their basal one. Neurons are also polarized since their dendritic, axonal, and even nerve terminal plasma membranes are all different. Neurons, however, are also polarized secretory cells in that they store neurotransmitter and neuropeptides in synaptic vesicles but release their secreted products only at the nerve terminal. As a consequence, the membrane sorting problem, a topic of much current study in polarized and secretory cells, is especially intriguing and challenging in the neuron. We can divide sorting into four major subdivisions, as shown in Figure 1.(1) After synthesis and glycosylation, dendritic membrane proteins must be segregated away from membrane proteins and neuropeptides destined for the nerve terminal. Axonal membrane polypeptides might take yet a third route. (2) The transport vesicles that carry the segregated proteins to their destinations and the synaptic vesicles must be correctly targeted, presumably in...