DISSECTING MOLECULAR AND GENETIC MECHANISMS THAT PROMOTE MYELINATION

描述(申请人提供)：髓鞘是一种多层膜，覆盖脊椎动物神经系统中的轴突。在外周神经系统中，被称为雪旺细胞的特殊神经胶质细胞将自己包裹在轴突片段周围，形成髓鞘。髓鞘对神经元的营养支持是必不可少的，并为有效地传导神经冲动提供绝缘。周围髓鞘的破坏可导致毁灭性的神经疾病，如夏科-玛丽-牙(CMT)病。目前还没有预防脱髓鞘或刺激再髓鞘形成的治疗方法，这些治疗方法的发展受到对驱动雪旺细胞形成髓鞘的遗传和分子因素的不完全了解的阻碍。雪旺细胞的髓鞘形成需要GPR126，这是一种孤立的黏附家族G蛋白偶联受体(AGPCR)。在脊椎动物模型中，GPR126功能的丧失会导致雪旺细胞在早幼粒状态的发育受阻，外周髓鞘减少或缺失。尽管GPR126对外周髓鞘形成是必不可少的，但人们对其作用机制知之甚少。本研究将利用斑马鱼模型系统来确定GPR126在髓鞘形成中的作用。在第一个目标中，我将使用结构-功能分析来定义GPR126的分子结构域，这些分子结构域调控外周髓鞘形成的关键步骤。我预测，GPR126的大N-末端结构域在对单个大口径轴突周围的每个雪旺细胞进行分类方面具有独特的功能。相反，我假设GPR126的跨膜C末端足以指导雪旺细胞在分选后包裹轴突。我 将产生特定的斑马鱼突变体，并在体内进行分析以检验这些假设。在我的第二个目标中，我将对GPR126亚型突变中增强或抑制髓鞘缺陷的突变进行创新的正向遗传筛查。这一增强子/抑制子筛选将识别GPR126髓鞘形成程序的调节因子以及与GPR126平行发挥髓鞘形成作用的新因子。通过定义促进髓鞘形成的分子和遗传因素，这些研究将为识别CMT等遗传性神经疾病的致病突变提供基础。这项工作还将加深我们对雪旺细胞生物学的理解，并可以为开发治疗脱髓鞘和促进周围神经髓鞘再分化的治疗方法奠定基础。

DESCRIPTION (provided by applicant): Myelin is a multilayered membrane that ensheathes axons in vertebrate nervous systems. In the peripheral nervous system, specialized glia called Schwann cells wrap themselves around axonal segments to form the myelin sheath. Myelin is essential for trophic support of neurons and provides insulation to efficiently conduct nerve impulses. Disruption of the peripheral myelin sheath can result in devastating neuropathies such as Charcot-Marie-Tooth (CMT) disease. There are currently no treatments to prevent de-myelination or stimulate re-myelination, and development of these therapies is hindered by an incomplete understanding of the genetic and molecular factors that drive Schwann cells to form the myelin sheath. Schwann cell myelination requires Gpr126, an orphaned adhesion family G protein-coupled receptor (aGPCR). Loss of Gpr126 function in vertebrate models results in arrested development of Schwann cells at the promyelinating state and reduced or absent peripheral myelin. Although Gpr126 is essential for peripheral myelination, very little is known about the mechanism by which it functions. This study will utilize the zebrafish model system to define the role of Gpr126 in myelination. In the first aim, I will use structure-function analysis o define the molecular domains of Gpr126 that regulate key steps in peripheral myelination. I predict that the large N-terminal domain of Gpr126 has a distinct function in sorting each Schwann cell around a single large-caliber axon. In contrast, I hypothesize the transmembrane C-terminus of Gpr126 is sufficient to direct the Schwann cell to wrap the axon following sorting. I will generate specific zebrafish mutants and perform in vivo analyses to test these hypotheses. In my second aim, I will perform an innovative forward genetic screen for mutations that enhance or suppress myelin defects in gpr126 hypomorphic mutants. This enhancer/suppressor screen will identify regulators of the Gpr126 myelination program as well as novel factors that function in parallel to Gpr126 for myelination. By defining the molecular and genetic factors that promote myelination, these studies will provide the basis for identifying causative mutations for genetic neuropathies like CMT. This work also will also deepen our understanding of Schwann cell biology and can lay the foundation for developing therapies to treat demyelination and promote re-myelination of peripheral nerves.