During development, neuronal growth cones encounter a variety of guida
nce cues while mediating axon pathfinding, target recognition and syna
pse formation. It is clear that repulsive guidance mechanisms play an
essential role in these processes. The semaphorin gene family, which i
s conserved from invertebrates to mammals, includes members that media
te repulsive guidance. Molecular and cellular analysis of this gene fa
mily is providing insight into how inhibitory cues function during neu
rodevelopment.