Semaphorin 3A (Sema3A) may play a particularly interesting role in limiting axon regeneration since it is expressed in meningeal fibroblasts that invade the injured spinal cord and surround the glial scar. In addition, the Sema3A co receptors, Neuropilin 1 and Plexin A1, are expressed on axons that regenerate up to the injured region, but do not cross this Sema3A containing region. Thus, Sema3A and its co receptors may have important roles in regulating axon guidance during neuronal development and after neuronal injury.