Regulation of Motor Axon Innervation at the Neuromuscular Junction

Neuromuscular Junction;Muscle Denervation;Semaphorin3A Signaling;RiboTag Mouse Model;Motor Axon Local Translation;Molecular;Cellular and Developmental Biology;Science;Cellular & Molecular Biology

Shadrach, JenniferHerzog, Susan Brooks ;

University of Michigan

关键词: Neuromuscular Junction;    Muscle Denervation;    Semaphorin3A Signaling;    RiboTag Mouse Model;    Motor Axon Local Translation;    Molecular;    Cellular and Developmental Biology;    Science;    Cellular & Molecular Biology;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/138447/jenshad_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Coordinated motor function is achieved by proper communication between motor neurons and muscle fibers at a specialized synapse called the neuromuscular junction (NMJ). Throughout life the maintenance of the NMJ is an active process that requires the coordinated function of three main players: the presynaptic motor neuron terminal, the postsynaptic muscle fiber, and terminal Schwann cells (TSCs). Both traumatic injury and neurodegenerative diseases, such as amyotrophic lateral sclerosis (ALS), can result in acute or chronic NMJ denervation, respectively. Under these conditions denervation triggers a regenerative response in which motor nerve terminals are stimulated to grow and undergo axonal sprouting as they reinnervate muscle fibers. Previous studies have suggested that reestablishment of neuromuscular connections is mediated by various axonal guidance molecules, of which Semaphorin3A (Sema3A) may be of particular importance. Sema3A is a secreted glycoprotein that binds to a plexinA-neuropilin-1 receptor complex to initiate a downstream signaling cascade that induces axonal repulsion. Interestingly, Sema3A mRNA upregulation at the NMJ has been hypothesized to create an inhibitory environment that limits axonal sprouting and dampens regeneration. However, a functional role for Sema3A at the NMJ has not been fully elucidated.Here, we established a quantitative and robust in vivo nerve crush model to examine NMJ reinnervation. Using this model, we examined how the ubiquitous loss of Sema3A or Npn1 impacts regeneration of the adult NMJ. Despite efficient deletion, disruption of Sema3A-Npn1 signaling had no detectable effect on NMJ reinnervation after injury. Thus, the utility of targeting this pathway may offer more limited therapeutic potential than suggested by earlier studies. To identify other promising signaling pathways involved in nerve regeneration, we developed a rapid and unbiased method to isolate motor neuron specific transcripts from complex tissues in vivo. Using the RiboTag transgenic mouse model, we show that ribosomal complexes and their associated mRNA transcripts can be specifically isolated from motor neurons and analyzed to detect changes in motor neurons gene expression following injury and during neurodegeneration. Coupling this technique with RNA-seq we anticipate that this work will guide the identification and development of novel therapeutic strategies to treat traumatic nerve injury and neurodegeneration.