The early neurite gets the axon

A developing neuron sprouts many neurites, only one of which will become the axon, while the rest form dendrites. Axon choice has been thought to result from competition among neurites, possibly for a growth promoter. But now, Froylan Calderon de Anda, Guilia Pollarolo, Jorge Santos Da Silva, Carlos Dotti, and colleagues (Universita degli Studi di Torino, Italy) show that the location of the axon is determined before most neurites form.

By the time the first neurite forms, the group finds, it already marks the location of the axon. No one has seen this association before because they have been looking at stage 2 neurons, which have already formed many neurites. “To find the specific molecular events that are instructions for polarity,” says Dotti, “we should look at the...