Semaphorin directs axon traffic in the fly olfactory system.

The convergence of olfactory sensory axons that express the same receptor onto specific glomeruli is a common organizing principle in animal olfactory systems. In this issue of Neuron, two beautiful studies in Drosophila by Lattemann et al. and Sweeney et al. show that Semaphorin repulsion regulates interactions between olfactory receptor neurons to help axons find their correct targets.