Axonal pathfinding during development needs appropriate responses to various attractive and repulsive guidance cues. The exact mechanisms by which different attractant/repulsion machineries interact or how the switch is precisely regulated at appropriate location are unknown. Here, Parra and Zou find that Sonic Hedgehog (Shh) can turn on Semaphorin repulsion via Shh receptors Patched-1 and Smoothened via the PKA pathway.
