Ph.D. Program for Neural Regenerative Medicine, College of Medical Science and Technology, Taipei Medical University and National Health Research Institutes, Taipei 110, Taiwan.
Department of Neurosurgery, Cathay General Hospital, Taipei 110, Taiwan.
J Neurosci. 2021 Apr 28;41(17):3808-3821. doi: 10.1523/JNEUROSCI.2863-20.2021. Epub 2021 Mar 16.
To assemble the functional circuits of the nervous system, the neuronal axonal growth cones must be precisely guided to their proper targets, which can be achieved through cell-surface guidance receptor activation by ligand binding in the periphery. We investigated the function of paxillin, a focal adhesion protein, as an essential growth cone guidance intermediary in the context of spinal lateral motor column (LMC) motor axon trajectory selection in the limb mesenchyme. Using mRNA detection, we first show paxillin expression in LMC neurons of chick and mouse embryos at the time of spinal motor axon extension into the limb. Paxillin loss-of-function and gain-of-function using electroporation in chick LMC neurons, of either sex, perturbed LMC axon trajectory selection, demonstrating an essential role of paxillin in motor axon guidance. In addition, a neuron-specific paxillin deletion in mice led to LMC axon trajectory selection errors. We also show that knocking down paxillin attenuates the growth preference of LMC neurites against ephrins , and erythropoietin-producing human hepatocellular (Eph)-mediated retargeting of LMC axons , suggesting paxillin involvement in Eph-mediated LMC motor axon guidance. Finally, both paxillin knockdown and ectopic expression of a nonphosphorylable paxillin mutant attenuated the retargeting of LMC axons caused by Src overexpression, implicating paxillin as a Src target in Eph signal relay in this context. In summary, our findings demonstrate that paxillin is required for motor axon guidance and suggest its essential role in the ephrin-Eph signaling pathway resulting in motor axon trajectory selection. During the development of neural circuits, precise connections need to be established among neurons or between neurons and their muscle targets. A protein family found in neurons, Eph, is essential at different stages of neural circuit formation, including nerve outgrowth and pathfinding, and is proposed to mediate the onset and progression of several neurodegenerative diseases, such as Alzheimer's disease. To investigate how Ephs relay their signals to mediate nerve growth, we investigated the function of a molecule called paxillin and found it important for the development of spinal nerve growth toward their muscle targets, suggesting its role as an effector of Eph signals. Our work could thus provide new information on how neuromuscular connectivity is properly established during embryonic development.
为了组装神经系统的功能电路，神经元轴突生长锥必须被精确地引导到它们的适当靶标，这可以通过配体结合在外周激活细胞表面导向受体来实现。我们研究了粘着斑蛋白 paxillin 的功能，作为脊椎外侧运动柱（LMC）运动轴突在肢体间质中选择轨迹的一个重要生长锥导向中介。通过 mRNA 检测，我们首先显示 chick 和 mouse 胚胎的 LMC 神经元在脊髓运动轴突延伸到肢体时表达 paxillin。使用 chick LMC 神经元的 电穿孔进行的 paxillin 功能丧失和功能获得实验，无论是雄性还是雌性，都扰乱了 LMC 轴突轨迹选择，证明了 paxillin 在运动轴突导向中的重要作用。此外，在小鼠中进行神经元特异性 paxillin 缺失导致 LMC 轴突轨迹选择错误。我们还表明，敲低 paxillin 会减弱 LMC 突起对 ephrins 的生长偏好，以及红细胞生成素产生的人肝细胞（Eph）介导的 LMC 轴突重定向，表明 paxillin 参与 Eph 介导的 LMC 运动轴突导向。最后，paxillin 敲低和非磷酸化 paxillin 突变体的异位表达都减弱了 Src 过表达引起的 LMC 轴突重定向，表明 paxillin 是 Eph 信号转导中 Src 靶标的在这种情况下。总之，我们的研究结果表明 paxillin 是运动轴突导向所必需的，并表明它在导致运动轴突轨迹选择的 ephrin-Eph 信号通路中具有重要作用。在神经网络回路的发育过程中，需要在神经元之间或神经元与其肌肉靶标之间建立精确的连接。在神经回路形成的不同阶段，包括神经生长和路径寻找，发现神经元中存在一个 Eph 蛋白家族是必不可少的，并且被提议介导几种神经退行性疾病的发生和进展，如阿尔茨海默病。为了研究 Eph 如何传递信号来介导神经生长，我们研究了一种称为 paxillin 的分子的功能，发现它对脊髓神经向其肌肉靶标生长很重要，这表明它是 Eph 信号的效应物。因此，我们的工作可以为胚胎发育过程中神经肌肉连接的正确建立提供新的信息。
