Bundle loss makes turning possible

Tightly bundled actin filaments direct axonal pathfinding, according to new study by Zhou et al. on page 839. The results identify how changes in actin structure control microtubule polymerization during neurite growth.As a neuron extends its axon, the growth cone turns toward certain cues and away from others. Turning involves collapse of lamellipodia to avoid the inhibitory signal and growth in a different direction. Although a requirement for actin and microtubules in this process is well established, how the two cytoskeletal elements change in response to avoidance cues was not known.

Zhou et al. have determined that disassembly of actin bundles is all that is necessary to initiate axon turning. In the absence of the bundles, force generated from actin retrograde flow toward the growth cone center prevents the...