Axon guidance: semaphorin/neuropilin/plexin signaling

The semaphorin protein family controls a wide variety of developmental processes in the nervous system such as axon guidance, cell migration, dendrite morphology, and synaptogenesis. The best characterized function of semaphorins is their ability to attract or repel neurites, directing these structures toward or away from specific regions. Although only a limited set of semaphorins has been identified, accumulating evidence indicates that distinct molecular mechanisms act to diversify the effects of these guidance cues, allowing them to control a disproportionally large number of different cellular events. In this chapter, we discuss general features and novel aspects of semaphorin function and signaling, including the role of their receptors: plexins and neuropilins. The focus is on the contribution of these molecules to the regulation of cell migration and the formation of neuronal connections. In addition, we highlight a few recent studies that examine how semaphorins, plexins, and/or neuropilins contribute to neurological diseases.