Department of Biologic and Materials Sciences, University of Michigan School of Dentistry, Ann Arbor, Michigan 48109.
Program in Cellular and Molecular Biology, University of Michigan School of Medicine, Ann Arbor, Michigan 48109.
eNeuro. 2018 May 16;5(3). doi: 10.1523/ENEURO.0155-17.2018. eCollection 2018 May-Jun.
The neuromuscular junction (NMJ) is a specialized synapse that is formed by motor axon innervation of skeletal muscle fibers. The maintenance of motor-muscle connectivity is critical for the preservation of muscle tone and generation of movement. Injury can induce a robust regenerative response in motor axons, but severe trauma or chronic denervation resulting from neurodegenerative disease typically leads to inefficient repair and poor functional recovery. The axon guidance molecule Semaphorin3A (Sema3A) has been implicated as a negative regulator of motor innervation. Upon binding to a plexinA-neuropilin1 (Npn1) receptor complex, Sema3A initiates a downstream signaling cascade that results in axonal repulsion. Here, we established a reproducible nerve crush model to quantify motor nerve regeneration. We then used that model to investigate the role of Sema3A signaling at the adult NMJ. In contrast to previous findings, we found that and mRNA decrease in response to denervation, suggesting that Sema3A-Npn1 signaling may regulate NMJ reinnervation. To directly test that hypothesis, we used inducible knockout models to ubiquitously delete Sema3A or Npn1 from adult mice. Despite demonstrating that we could achieve highly efficient gene deletion, disruption of Sema3A-Npn1 signaling did not affect the normal maintenance of the NMJ or disrupt motor axon reinnervation after a denervating injury.
神经肌肉接头（NMJ）是一种由运动轴突支配骨骼肌纤维形成的特化突触。运动肌连接的维持对于维持肌肉张力和产生运动至关重要。损伤可诱导运动轴突产生强烈的再生反应，但严重创伤或神经退行性疾病引起的慢性去神经支配通常导致修复效率低下和功能恢复不良。轴突导向分子 Semaphorin3A（Sema3A）被认为是运动神经支配的负调节剂。与 plexinA-神经纤毛蛋白 1（Npn1）受体复合物结合后，Sema3A 启动下游信号级联反应，导致轴突排斥。在这里，我们建立了一个可重复的神经挤压模型来定量测量运动神经再生。然后，我们使用该模型研究 Sema3A 信号在成人 NMJ 中的作用。与先前的发现相反，我们发现 和 mRNA 随去神经而减少，这表明 Sema3A-Npn1 信号可能调节 NMJ 再支配。为了直接检验这一假设，我们使用诱导型敲除模型在成年小鼠中普遍敲除 Sema3A 或 Npn1。尽管我们证明可以实现高效的基因缺失，但 Sema3A-Npn1 信号的破坏并不影响 NMJ 的正常维持，也不会在去神经损伤后破坏运动轴突再支配。
