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. Degree Type Dissertation Degree Name Doctor of Philosophy (PhD) Graduate Group Neuroscience First Advisor Michael Granato Subject Categories Biology | Neuroscience and Neurobiology This dissertation is available at ScholarlyCommons: https://repository.upenn. edu/edissertations/2318 NEUROMUSCULAR SYNAPTIC PROTEINS IN DEVELOPMENT AND REGENERATION Katherine D. Gribble A DISSERTATION in Neuroscience Presented to the Faculties of the University of Pennsylvania in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy 2017 Supervisor of Dissertation __________________________ Michael Granato, Ph.D. Professor of Cell and Developmental Biology Graduate Group Chairperson __________________________ Joshua Gold, Ph.D. Professor of Neuroscience Dissertation Committee: Jonathan Raper, Ph.D., Professor of Neuroscience Greg Bashaw, Ph.D., Professor of Neuroscience Judith Grinspan, Ph.D., Research Professor of Neurology Wenqin Luo, M.D., Ph.D., Assistant Professor of Neuroscience NEUROMUSCULAR SYNAPTIC PROTEINS IN DEVELOPMENT AND REGENERATION COPYRIGHT 2017 Katherine Diane Gribble This work is licensed under the Creative Commons AttributionNonCommercial-ShareAlike 3.0 License To view a copy of this license, visit https://creativecommons.org/licenses/by-nc-sa/3.0/us/