Specificity of Monosynaptic Sensory-Motor Connections Imposed by Repellent Sema3E-PlexinD1 Signaling

•Sema3E is expressed selectively by gluteus, but not hamstring, motor neurons•PlexinD1+ proprioceptive sensory afferents avoid Sema3E+ motor neuron pools•Ectopic Sema3E reduces the incidence of inputs from cognate sensory neurons•Attenuation of Sema3E or PlexinD1 results in aberrant monosynaptic connectivity

SummaryIn mammalian spinal cord, group Ia proprioceptive afferents form selective monosynaptic connections with a select group of motor pool targets. The extent to which sensory recognition of motor neurons contributes to the selectivity of sensory-motor connections remains unclear. We show here that proprioceptive sensory afferents that express PlexinD1 avoid forming monosynaptic connections with neurons in Sema3E+ motor pools yet are able to form direct connections with neurons in Sema3Eoff motor pools. Anatomical and electrophysiological analysis of mice in which Sema3E-PlexinD1 signaling has been deregulated or inactivated genetically reveals that repellent signaling underlies aspects of the specificity of monosynaptic sensory-motor connectivity in these reflex arcs. A semaphorin-based system of motor neuron recognition and repulsion therefore contributes to the formation of specific sensory-motor connections in mammalian spinal cord.

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