ETS gene Er81 controls the formation of functional connections between group Ia sensory afferents and motor neurons

The connections formed between sensory and motor neurons (MNs) play a criti cal role in the control of motor behavior. During development, the axons of proprioceptive sensory neurons project into the spinal cord and form both direct and indirect connections with MNs. Two ETS transcription factors, ER 81 and PEAS, are expressed by developing proprioceptive neurons and MNs, ra ising the possibility that these genes are involved in the formation of sen sory-motor connections. Er81 mutant mice exhibit a severe motor discoordina tion, yet the specification of MNs and induction of muscle spindles occurs normally. The motor defect in Er81 mutants results from a failure of group la proprioceptive afferents to form a discrete termination zone in the vent ral spinal cord. As a consequence there is a dramatic reduction in the form ation of direct connections between proprioceptive afferents and MNs. ER81 therefore controls a late step in the establishment of functional sensory-m otor circuitry in the developing spinal cord.