Uncovering the molecular mechanisms underlying spinal cord regeneration

在英国，每年大约有1200人因脊髓损伤而瘫痪。这是因为涉及中枢神经系统（CNS）的损伤具有非常差的再生能力，从而导致永久性功能丧失。然而，虽然脊髓损伤对人类来说是毁灭性的，但爪蟾的蝌蚪在截肢或受伤后可以完全再生其中枢神经系统（脊髓）。我们的目标是了解爪蟾的神经元再生如何发生，为脊髓损伤或周围神经病变患者开辟新的治疗途径。最近，我们发现转录因子Foxm1在爪蟾的再生脊髓中被特异性上调（Love et al. 2011）。初步数据表明，敲低foxm1表达会损害截肢后的尾巴再生，导致再生脊髓中增殖减少和神经元祖细胞增加。我们还使用Crispr/Cas9技术在爪蟾中产生了foxm1的敲除。该项目的第一个目标是利用foxm1基因敲除系进一步研究foxm1在脊髓再生中的作用。我们的第二个目标是进行RNAseq实验，以确定以Foxm1依赖和独立的方式参与脊髓再生的新基因。这些数据集将使我们能够开始揭示爪蟾尾巴截肢后脊髓再生的分子机制。由于这个项目的最终目标将是提高我们对为什么两栖动物比哺乳动物有更大的神经元再生能力的理解，这个项目的第三个目标将是比较我们在蝌蚪和哺乳动物身上的发现，使用啮齿动物的坐骨神经挤压作为神经再生的实验模型。先前的研究表明，Foxm1在坐骨神经受压后损伤部位表达上调，但其在再生中的作用尚不清楚。我们将首先确定哪种细胞类型表达Foxm1（神经中的雪旺细胞或轴突）。然后，我们将测试我们已经确定的爪蟾再生和Foxm1依赖基因是否也在坐骨神经挤压时上调。最后，我们将使用遗传工具，如条件Foxm1敲除小鼠来评估其在再生中的作用。总之，这些实验将大大提高我们对神经元再生的分子机制的理解。我们希望它最终将开辟新的研究途径，以改善哺乳动物和人类的神经元再生。

About 1200 people a year are left paralysed in the UK due to a Spinal Cord Injury (or SCI). This is because injuries involving the central nervous system (CNS) have very poor capacities to regenerate, thus resulting in a permanent loss of function. However, whilst SCI can be devastating to humans the tadpole of the frog Xenopus can regenerate their CNS (spinal cord) completely following amputation or injury. Our goal is to understand how neuronal regeneration occurs in Xenopus to open new therapeutic avenues for patients suffering a SCI or peripheral neuropathies. Recently, we have identified the transcription factor Foxm1 as being specifically upregulated in the regenerating spinal cord in Xenopus (Love et al. 2011). Preliminary data indicate that knocking down foxm1 expression impairs tail re-growth upon amputation, leads to a reduction of proliferation and an increase of neuronal progenitors in the regenerating spinal cord. We have also generated a knockout of foxm1 in Xenopus using the Crispr/Cas9 technology. The first aim of this project will be to use our foxm1 knockout line to investigate further the role of Foxm1 during spinal cord regeneration. Our second aim will be to perform an RNAseq experiments to identify new genes involved in spinal cord regeneration in a Foxm1 dependent and independent manner. These datasets will allow us to start uncovering the molecular mechanisms underlying spinal cord regeneration following tail amputation in Xenopus. Since the ultimate goal of this project will be to improve our understanding of why amphibians have greater capacity for neuronal regeneration than mammals, the third aim of this project will be to compare our findings in tadpoles with those in mammals, using the sciatic nerve crush in rodents as an experimental model of nerve regeneration. It has previously been shown that Foxm1 expression is upregulated at the site of injury following sciatic nerve crush, but its role in regeneration is unknown. We will first establish which cell type(s) expressed Foxm1 (Schwann cells or axons in the nerve). We will then test if the genes we have identified as being regeneration and Foxm1 dependant in Xenopus are also upregulated upon sciatic nerve crush. Finally, we will use genetic tools such as conditional Foxm1 knock-out mice to assess its role in regeneration.Altogether, these experiments will greatly improve our understanding of the molecular mechanisms underlying neuronal regeneration. We hope that it will ultimately open new research avenues to improve neuronal regeneration in mammals and humans.