Coreceptor for SEMA3A. Necessary for signaling by class 3 semaphorins and subsequent remodeling of the cytoskeleton. Plays a role in axon guidance in the developing nervous system. Class 3 semaphorins bind to a complex composed of a neuropilin and a plexin. The plexin modulates the affinity of the complex for specific semaphorins, and its cytoplasmic domain is required for the activation of down-stream signaling events in the cytoplasm. Interacts with NRP1 and NRP2. Expressed in the developing nervous system. Widely expressed in both the central and peripheral nervous systems. Expressed in the peripheral ganglia, somatosensory, olfactory, visual, auditory and equilibrium systems. No visible phenotype. Mice exhibit defasciculation of the facial branchiomotor nerve and of the ophthalmic branch of the trigeminus, with variable severity. In mice lacking both Plxna3 and Plxna4, migrating neurons do not show the normal response to Sema3A and Sema3F and do not migrate away from these semaphorins (in vitro). Belongs to the plexin family. Truncated N-terminus.