Hox genes: the instructors working at motor pools.

Motor neurons are assigned unique subidentities preceding their axon navigation. This ensures proper innervation of muscle targets and is accompanied by a stereotypical clustering of motor neuron cell bodies into "motor pools" within the spinal cord. However, the mechanisms that drive motor neuron diversification have been poorly understood. A new study by Dasen et al. (2005) in this issue of Cell shows that a network of Hox genes is responsible for instructing motor pool development.