The peroneal muscular atrophy mousehas aberrant projection of spinal motor axons to the gluteal region.

The peroneal muscular atrophy (pma) mouse shows congenital clubfoot due to atrophy of the peroneal muscles caused by lack of peroneal nerve innervation. Although it was reported that the peroneal nerve was absent in pma embryos, specific analysis of motor axon development in pma embryos has not been performed. Here, we generated a transgenic pma mouse that expresses enhanced green fluorescent protein (EGFP) in the spinal motor neurons, and examined the motor nerve trajectory specifically using wholemount preparations and three-dimensional reconstruction of EGFP-immunostained fibers. At embryonic day 11.5, when the sciatic nerve began to grow out of the spinal cord, no apparent differences were observed between the control and pma mice. From embryonic days 12.0 to 13.5, in the control mouse, the peroneal and tibial nerves extended into the hindlimb bud, whereas in the pma mouse, the tibial nerve formed normally but the peroneal nerve was never observed in its proper position. Moreover, an abnormal EGFP-positive axon bundle was observed near the gluteal nerve in the hip region. These results indicate that the pma mouse has axon guidance defects in the spinal motor neurons in addition to lack of the peroneal nerve.