Subhojit Roy, Matthew J. Winton, Mark M. Black, John Q. Trojanowski, and Virginia M.-Y. Lee

This week, Roy et al. monitored traffic in the fast and slow lanes of axons. Proteins are transported to distal axons in three distinct groups: fast component (FC), slow component-a (SCa), and slow component-b (SCb). The well described FC and SCa mechanisms move vesicular and structural cargoes, respectively, to axons at vastly different speeds. SCb hauls loads such as proteins involved in axon growth at about 2-C10 times the speed of SCa. The authors visualized SCb transport in live hippocampal neurons transfected with combinations of three fluorescently tagged SCb proteins: -synuclein, synapsin-I, and glyceraldehyde-3-phosphate dehydrogenase, as well as the FC protein synaptophysin. A direct comparison of -synuclein and synaptophysin transport revealed that SCb transport was much slower overall, but it had a herky-jerky quality, and its instantaneous velocity was surprisingly comparable with FC. Like SCa transport, the stop-and-go movement of the multiprotein SCb complexes slows traffic.

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