Cellular and molecular mechanisms of peripheral nerve regeneration

周围神经系统保留了显著的轴突再生能力。作为对.的回应 损伤，特征明确的神经元内部信号通路启动再生反应，最终 导致轴突生长锥体喷出。在明确定义的生长因素的推动下，生长锥体沿着 失神经的雪旺细胞，它们利用作为一般的再生途径，但在分支点个别 再生轴突必须选择通往其原始目标的正确路径。虽然是准确的 轴突再生到其原始靶点对于细胞和分子的功能恢复至关重要。 再生轴突选择原始目标的机制还不是很清楚。 我们最近建立了一个活体系统来监测和量化活体靶点选择性神经再支配 完好无损的动物。利用这一系统，我们发现在背侧和腹侧运动神经横断后 分支，再生的斑马鱼运动轴突表现出强烈的偏爱它们原来的肌肉区域， 为靶标选择性再生的分子机制的存在提供了令人信服的证据。至 确定这一过程背后的基因我们调查了在神经中具有已知作用的基因的突变 发展。我们确定了四个基因，它们本身并不促进轴突再生，而是提供靶向。 再生轴突的选择性。该方案中的实验建立在突变体中的发现基础上 ROBO2引导受体和exostosin like 3(Ext13)糖基转移酶运动轴突发育正常 但再生的背神经轴突经常选择不正确的、异位的轨迹，侵犯外侧和腹侧 领地。虽然这两个基因在神经发育中都发挥着明确的作用，但它们在再生方面的功能却不是这样 明白了。这项提案中的实验将确定这两个基因促进 目标选择性再生。在目标1中，我们将确定ROBO2通过 在再生中起作用，例如作为轴突狭缝受体，或者作为雪旺细胞受体。在《目标2》中，我们 将决定ROBO2引导背神经再生的细胞机制，例如通过纠正 在选择点上的寻路错误，和/或通过将先锋轴突引向其原始路径， 从而为跟随者轴突提供再生途径。最后，在目标3中，我们将确定 Exostosin like 3(Ext13)通过其在硫酸乙酰肝素生产中的作用或通过其 独特的表面受体结构域。总而言之，拟议的研究将对 研究被切断的轴突如何回到其原始目标的基础科学。这将带来更好的结果 全面了解周围神经再生，将有助于解决紧急情况 糖尿病、损伤和糖尿病引起的周围神经病变患者的治疗需求 自身免疫性疾病。

The peripheral nervous system has retained a remarkable capacity for axonal regeneration. In response to injury, well-characterized neuron intrinsic signaling pathways mount a regenerative response that eventually leads to spouting of axonal growth cones. Promoted by well-defined growth factors, growth cones extend along denervated Schwann cells that they utilize as a general regeneration pathway, yet at branch points individual regenerating axons have to select the correct path towards their original targets. Although accurate regeneration of axons to their original targets is critical for the functional recovery, the cellular and molecular mechanisms by which regenerating axons select their original targets are not well understood. We recently established an in vivo system to monitor and quantify target selective re-innervation in live intact animals. Using this system we discovered that following transection of the dorsal and ventral motor nerve branch, regenerating zebrafish motor axons exhibit a strong preference for their original muscle territory, providing compelling evidence for the existence of molecular mechanisms for target-selective regeneration. To identify the genes underlying this process we surveyed mutants in genes with known roles in neural development. We identified four genes that do not promote axonal regrowth per se, but rather provide target selectivity to regenerating axons. The experiments in this proposal build upon the findings that in mutants for the robo2 guidance receptor and for the exostosin like 3 (extl3) glycosyltranferase motor axons develop normal but regenerating dorsal nerve axons frequently select incorrect, ectopic trajectories, invading lateral and ventral territories. While both genes play well-defined roles in neural development, their function in regeneration is not understood. The experiments in this proposal will define the mechanisms by which these two genes promote target selective regeneration. In Aim 1 we will determine the molecular mechanisms through which robo2 functions in regeneration, e.g. as an axonal Slit receptor, or alternatively as Schwann cell receptor. In Aim 2 we will determine the cellular mechanisms by which robo2 guides dorsal nerve regeneration, e.g. by correcting pathfinding mistakes at the choice point, and/or by directing pioneering axons towards their original path, thereby providing a regeneration pathways for follower axons. Finally, in Aim 3 we will determine whether exostosin like 3 (extl3) guides regenerating axons through its role in heparan sulfate production or via its unique surface receptor domain. Combined, the proposed studies will make significant contributions to the fundamental science of how transected axons return to their original targets. This will results in a better understanding of peripheral nerve regeneration across the board and will help to address the urgent therapeutic needs for patients suffering from peripheral neuropathies caused by diabetes, injury, and autoimmune disorders.