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.

Graphical AbstractFigure optionsDownload as PowerPoint slide