Plexin A is a neuronal semaphorin receptor that controls axon guidance

The Semaphorins comprise a large family of secreted and transmembrane prote ins, some of which function as repellents during axon guidance. Semaphorins fall into seven subclasses. Neuropilins are neuronal receptors for class I II Semaphorins. In the immune system, VESPR, a member of the Plexin family, is a receptor for a viral-encoded Semaphorin. Here, we identify two Drosop hila Plexins, both of which are expressed in the developing nervous system. We present evidence that Plexin A is a neuronal receptor for class I Semap horins (Sema 1a and Sema 1b) and show that Plexin A controls motor and CNS axon guidance. Plexins, which themselves contain complete Semaphorin domain s, may be both the ancestors of classical Semaphorins and binding partners for Semaphorins.