Plexin-A3 mediates semaphorin signaling and regulates the development of hippocampal axonal projections

Plexins are receptors implicated in mediating signaling by semaphorins, a f amily of axonal chemorepellents. The role of specific plexins in mediating semaphorin function in vivo has not, however, yet been examined in vertebra tes. Here, we show that plexin-A3 is the most ubiquitously expressed plexin family member within regions of the developing mammalian nervous system kn own to contain semaphorin-responsive neurons. Using a chimeric receptor con struct, we provide evidence that plexin-A3 can transduce a repulsive signal in growth cones in vitro. Analysis of plexin-A3 knockout mice shows that p lexin-A3 contributes to Sema3F and Sema3A signaling and that plexin-A3 regu lates the development of hippocampal axonal projections in vivo.