No endocytosis in the axonal entry

It takes two steps to localize a sodium channel to its proper location at the entrance to the axon, based on results on page 571 from Fache et al. Their findings are consistent with a targeting system involving both tethering and selective elimination.

The boundary between the neuronal cell body and the axon, called the axonal initial segment (AIS), is a dense network of actin and ankyrin G and β IV spectrin, where clusters of sodium channels initiate action potentials. A cytoplasmic loop from the Na_v1.2 sodium channel binds to ankyrin and, when added to non-AIS proteins, can direct them to this segment. The authors now show that this loop contains two separate domains essential for precise localization.

One domain tethers the protein to ankyrin, and the other removes it from surface of the...