C3 and CD47 mediate sensory-motor circuit refinement during spinal cord development.

C3 and CD47 mediate elimination of supernumerary proprioceptive synapses in developing spinal circuits, ensuring proper motor control in mammals.

• Why it matters: Understanding how sensory-motor circuits are refined during development is crucial for insights into motor control and potential neurological disorders. The mechanisms behind synapse pruning in the spinal cord remain largely unknown, limiting knowledge of circuit maturation.
• What they did: Using mouse genetics, circuit mapping, electrophysiology, and behavioral analyses, the study identified supernumerary proprioceptive synapses that form inappropriate contacts with motor neurons and are functionally active, impairing behavior. It revealed two mechanisms—C3 via the classical complement pathway and CD47 independently—responsible for their elimination.
• The result: The dual fail-safe system involving C3 and CD47 ensures the removal of inappropriate synapses, facilitating the development of mature spinal motor circuits and proper motor function.