Semaphorin-mediated axonal guidance via Rho-related G proteins

For many growing axons, interaction with an extracelluar Semaphorin signal leads to growth cone collapse and axon repulsion. Semaphorin receptors comp osed of Neuropilins and Plexins transduce extracellular cues into changes i n the growth cone actin cytoskeleton. The data implicating Rho family G pro teins in Semaphorin signaling and in other axon guidance events are conside red here. Recent work makes it clear that Rac1 is required for this process . In particular, there is intriguing new evidence that the Plexin receptors communicate directly with members of the Rho family GTPases, although unce rtainties remain concerning how Plexins alter Rac1 function. The CRMP (coll apsin response mediator protein) family is also required for Plexin-based S emaphorin signaling, and new data demonstrate direct links to Rho and Rac1- based signaling.