The role of selective transport in neuronal protein sorting

To assess whether selective microtubule-based vesicle transport underlies t he polarized distribution of neuronal proteins, we expressed green fluoresc ent protein- (GFP-) tagged chimeras of representative axonal and dendritic membrane proteins in cultured hippocampal neurons and visualized the transp ort of carrier vesicles containing these proteins in living cells. Vesicles containing a dendritic protein, transferrin receptor (TfR), were preferent ially transported into dendrites and excluded from axons. In contrast, vesi cles containing the axonal protein NgCAM (neuron-glia cell adhesion molecul e) were transported into both dendrites and axons. These data demonstrate t hat neurons utilize two distinct mechanisms for the targeting of polarized membrane proteins, one (for dendritic proteins) based on selective transpor t, the other (for axonal proteins) based on a selectivity "filter" that occ urs downstream of transport.