Muñoz Rosana, Edwards-Faret Gabriela, Moreno Mauricio, Zuñiga Nikole, Cline Hollis, Larraín Juan
Center for Aging and Regeneration, Millennium Nucleus in Regenerative Biology, Faculty of Biological Sciences, P. Universidad Católica de Chile, Alameda 340, Santiago, Chile.
The Dorris Neuroscience Center, Department of Molecular and Cellular Neuroscience, The Scripps Research Institute, La Jolla, CA 92037, United States.
Dev Biol. 2015 Dec 15;408(2):229-43. doi: 10.1016/j.ydbio.2015.03.009. Epub 2015 Mar 19.
Spinal cord regeneration is very inefficient in humans, causing paraplegia and quadriplegia. Studying model organisms that can regenerate the spinal cord in response to injury could be useful for understanding the cellular and molecular mechanisms that explain why this process fails in humans. Here, we use Xenopus laevis as a model organism to study spinal cord repair. Histological and functional analyses showed that larvae at pre-metamorphic stages restore anatomical continuity of the spinal cord and recover swimming after complete spinal cord transection. These regenerative capabilities decrease with onset of metamorphosis. The ability to study regenerative and non-regenerative stages in Xenopus laevis makes it a unique model system to study regeneration. We studied the response of Sox2(/)3 expressing cells to spinal cord injury and their function in the regenerative process. We found that cells expressing Sox2 and/or Sox3 are present in the ventricular zone of regenerative animals and decrease in non-regenerative froglets. Bromodeoxyuridine (BrdU) experiments and in vivo time-lapse imaging studies using green fluorescent protein (GFP) expression driven by the Sox3 promoter showed a rapid, transient and massive proliferation of Sox2(/)3(+) cells in response to injury in the regenerative stages. The in vivo imaging also demonstrated that Sox2(/)3(+) neural progenitor cells generate neurons in response to injury. In contrast, these cells showed a delayed and very limited response in non-regenerative froglets. Sox2 knockdown and overexpression of a dominant negative form of Sox2 disrupts locomotor and anatomical-histological recovery. We also found that neurogenesis markers increase in response to injury in regenerative but not in non-regenerative animals. We conclude that Sox2 is necessary for spinal cord regeneration and suggest a model whereby spinal cord injury activates proliferation of Sox2/3 expressing cells and their differentiation into neurons, a mechanism that is lost in non-regenerative froglets.
脊髓再生在人类中效率极低，会导致截瘫和四肢瘫痪。研究能够在脊髓损伤后进行再生的模式生物，可能有助于理解细胞和分子机制，从而解释为何该过程在人类中失败。在此，我们使用非洲爪蟾作为模式生物来研究脊髓修复。组织学和功能分析表明，变态前阶段的幼体在脊髓完全横断后可恢复脊髓的解剖连续性并恢复游泳能力。这些再生能力随着变态的开始而下降。在非洲爪蟾中研究再生和非再生阶段的能力使其成为研究再生的独特模式系统。我们研究了表达Sox2/3的细胞对脊髓损伤的反应及其在再生过程中的功能。我们发现，表达Sox2和/或Sox3的细胞存在于再生动物的脑室区，而在非再生幼蛙中则减少。使用由Sox3启动子驱动的绿色荧光蛋白（GFP）表达进行的溴脱氧尿苷（BrdU）实验和体内延时成像研究表明，在再生阶段，Sox2/3(+)细胞会因损伤而迅速、短暂且大量增殖。体内成像还表明，Sox2/3(+)神经祖细胞会因损伤而生成神经元。相比之下，这些细胞在非再生幼蛙中表现出延迟且非常有限的反应。敲低Sox2以及过表达显性负性形式的Sox2会破坏运动功能以及解剖组织学恢复。我们还发现，神经发生标记物在再生动物中会因损伤而增加，而在非再生动物中则不会。我们得出结论，Sox2是脊髓再生所必需的，并提出了一个模型，即脊髓损伤会激活表达Sox2/3的细胞增殖并使其分化为神经元，而非再生幼蛙则失去了这一机制。
