Neuromuscular Synaptic Proteins In Development And Regeneration


Following injury, peripheral nerves reestablish neuromuscular connections with their developmental targets. While the molecular pathways that govern peripheral nerve development and neuromuscular synapse formation are mostly understood, it is unclear whether the same pathways are reemployed to promote regeneration. For example, neuromuscular synapses form through the Agrin-Lrp4-MuSK signaling pathway that clusters acetylcholine receptors beneath motor axon terminals, yet in vivo role of this pathway in peripheral nerve regeneration has not been examined. To determine whether this pathway is employed during regeneration, I used a previously established assay to transect spinal motor nerves and continuously monitor regeneration in live, intact zebrafish. Using live imaging I find that in zebrafish pioneering axons establish a regenerative path for follower axons. I find that this process requires the synaptic receptor lrp4 and that in lrp4 mutants pioneer axon regrowth is unaffected while follower axons frequently stall at the site of injury, providing evidence for molecular diversity between pioneering and follower axons during regeneration. I demonstrate that Lrp4 promotes regeneration independent of membrane anchoring and of MuSK co-receptor signaling essential for synaptic development. Finally, I show that Lrp4 coordinates the realignment of denervated Schwann cells with regenerating axons, consistent with a model by which Lrp4 is repurposed to promote sustained peripheral nerve regeneration via axon-glia interactions. In a broader context, my findings demonstrate that certain molecular players involved in development are reused in regeneration in novel contexts, lending credence to the argument that studying mechanisms of synapse development enhances our understanding of mechanisms of peripheral nerve regeneration.

Michael Granato
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