Fine-tuning motor neuron properties: Signaling from the periphery

Our understanding of motor neuron differentiation is rapidly evolving. New studies demonstrate that cells in the periphery of the embryo provide feedback signals for spinal cord motor neurons that are instrumental in the timing and regulation of their development. Two papers in this issue of Neuron (Haase et al., 2002; Livet et al., 2002) identify a motor neuron survival factor, GDNF, and the ETS transcription factor, PEA3, as key components of a signal transduction pathway whose goals are 2-fold: to cluster motor pool-specific cell bodies and to promote axon arborization.