Arp2/3 for axon turning

Axons miss turning signals if they do not have the Arp2/3 complex to slow them down, according to Geraldine Strasser, Lorene Lanier (University of Minnesota, Minneapolis, MN), and colleagues.

Arp2/3 forms short, branched actin filaments in lamellipodia to drive movement in fibroblasts. Axons, however, do not need Arp2/3 activity for forward momentum, as the authors show that axons are longer if Arp2/3 is inhibited. But these axons did not change direction in response to guidance cues. They passed straight over inhibitory signals rather than turning away.

Longer axons usually have very stable microtubules, but the long Arp2/3-less axons had overly dynamic microtubules. Their instability may impair the coordination of actin and microtubule networks that is needed for growth cone turning. “The microtubules are out of control,” says Lanier. “Like on a highway, if you go...