Semaphorin function in the developing invertebrate peripheral nervous system

Different members of the semaphorin family of secreted and transmembrane gu idance molecules play important and diverse roles during neuronal developme nt. Within the developing grasshopper limb bud, two semaphorins are express ed in relatively non-overlapping and distinct expression patterns. The esta blishment of the tibial sensory projection within the limb bud relies on th e combinatorial action of both semaphorins. In this review, we describe the function of the two semaphorins in axonal guidance and propose that a hier archy of cues guide sensory neurons in the developing peripheral nervous sy stem.