Plays a role in growth cones guidance. Required for both proper adult behavior and survival. Can function in vivo as a selective target-derived signal that inhibits the formation of specific synaptic terminal arbors. Interacts with PlexB. Transiently expressed by a single large muscle during motoneuron outgrowth and synapse formation. Expression begins around stage 10 in weak epidermal stripes. Nervous system expression is first detected around stage 15 and at stage 16 appears to remain restricted to a small subset of neurons. Beginning around stage 14, it is also expressed at a very high level in a single ventral thoracic muscle fiber in segment T3. It is also expressed in the embryonic gonads and in anterior sensory organs, including the maxillary complex. Belongs to the semaphorin family.