Investigation on the role of retinoids and RAR beta in neural development and regeneration

在胚胎发育过程中，许多不同的机制被用来引导生长的轴突到达合适的目标。其中一种机制是化学吸引，其中靶组织释放因子来吸引生长的轴突。我们实验室最近的工作结果已经确定了一种小的脂溶性维生素a代谢物，全反式维甲酸（RA），是蝾螈脊髓再生过程中的关键因素。此外，我们已经证明这种分子对池塘蜗牛神经元的生长和定向生长（趋化性）有类似的影响，这表明在发育和再生神经找到目标的机制中存在一些进化守恒。在本文中，我们计划进一步研究RA及其核受体之一视黄酸受体β (RARb)在成年蝾螈脊髓再生中的作用。值得注意的是，rbeta存在于胚胎小鼠的脊髓中（可以再生），但在成年小鼠的脊髓中不存在（在出生前就失去了这种能力）。我们最近分离并克隆了这种受体的蝾螈同源物。我们将确定它的时间和空间表达模式在再生脊髓的截肢尾巴。我们还将通过一种称为RNA干扰的过程，通过实验减少该受体在再生成年蝾螈脊髓中的表达，以确定再生是否依赖于其持续表达，就像在哺乳动物胚胎中一样。这些研究将补充那些计划确定脊髓损伤后内源性RA合成水平的研究，以及那些确定脊髓细胞中受体调节的基因产物类型的研究。了解成年蝾螈中枢神经系统的创伤诱导再生过程，以及确定神经元生长和定向寻径所需的因素，对于设计治疗策略以防止神经细胞变性和重新刺激成年哺乳动物（包括人类）的胚胎通路具有重要意义。

During embryonic development, a number of different mechanisms are employed to guide growing axons to their appropriate targets. One such mechanism is chemoattraction, wherein factors are released by the target tissues to attract growing axons. Results from recent work in our lab have identified a small, lipid-soluble vitamin A metabolite, all-trans retinoic acid (RA), as a critical factor in this process in newt spinal cord regeneration. Moreover, we have shown that this molecule has similar effects on outgrowth and directional growth (chemotaxis) on neurons from the pond snail, Lymnaea stagnalis, suggesting some evolutionary conservation in the mechanisms by which developing and regenerating nerves find their targets. In this proposal, we plan to further investigate the role of RA and one of its nuclear receptors, retinoic acid receptor beta (RARb) in spinal cord regeneration in adult newts. Significantly, RARbeta is found in embryonic mouse spinal cords (which can regenerate), but is absent in adult mouse spinal cords (which lose this ability before birth. We have recently isolated and cloned the newt homologue of this receptor. We will determine its temporal and spatial patterns of expression in the regenerating spinal cord in amputated tails. We will also experimentally diminish the expression of this receptor in regenerating adult newt spinal cords by a process called RNA interference, to determine if regeneration is dependent upon its continual expression, as it appears to be in mammalian embryos. These studies will supplement those planned to determine the level of synthesis of endogenous RA in the spinal cords as a consequence of injury as well as those to determine the types of gene products regulated by the receptor in spinal cord cells. Understanding the trauma-induced regeneration processes in the adult newt CNS, as well as identifying the factors required for neuronal outgrowth and directional pathfinding, are important for designing therapeutic strategies to prevent nerve cell degeneration and to restimulate the embryonic pathway in adult mammals, including humans.