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。响应于 损伤后，充分表征神经元内在信号传导通路产生再生反应， 导致轴突生长锥的喷出。在明确的生长因子的促进下，生长锥沿着 失神经的雪旺细胞，他们利用作为一般的再生途径，但在分支点个别 再生轴突必须选择正确的路径到达它们的原始目标。虽然准确 轴突向其原始靶的再生对于功能恢复、细胞和分子损伤是至关重要的。 再生轴突选择其原始目标的机制还没有很好的理解。 我们最近建立了一个在体系统，以监测和量化目标选择性神经再支配在生活 完整的动物使用这个系统，我们发现，在切断背侧和腹侧运动神经后， 分支，再生的斑马鱼运动轴突表现出对它们原始肌肉区域的强烈偏好， 为靶选择性再生的分子机制的存在提供了令人信服的证据。到 为了确定这一过程背后的基因，我们调查了在神经系统中具有已知作用的基因中的突变体。 发展我们发现了四个基因，它们本身并不促进轴突再生，而是提供靶向神经再生的基因。 选择性再生轴突。这项提议中的实验是建立在这样的发现之上的： ROB 2引导受体和外生骨疣素样3（EXT 13）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错误的异位轨迹，侵入外侧和腹侧， 领土虽然这两个基因在神经发育中发挥着明确的作用，但它们在再生中的功能却不是 明白在这项建议中的实验将确定这两个基因促进的机制， 目标选择性再生。在目标1中，我们将确定robo 2 在再生中起作用，例如作为轴突Slit受体，或者作为雪旺细胞受体。在目标2中， 将确定robo 2引导背神经再生的细胞机制，例如通过纠正 在选择点的寻路错误，和/或通过引导先驱轴突朝向它们的原始路径， 从而为跟随轴突提供再生途径。最后，在目标3中，我们将确定 外生骨素样3（extl 3）通过其在硫酸乙酰肝素产生中的作用或通过其在神经元中的作用来引导再生轴突。 独特的表面受体结构域。综合起来，拟议的研究将对 切断的轴突如何回到原来的目标的基础科学。这将导致更好的 全面了解周围神经再生，将有助于解决紧迫的 糖尿病引起的周围神经病变患者的治疗需求，损伤， 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.