Roles of the X-linked Intellectual Disability gene ZDHHC9 in White Matter formation

摘要： 在中枢神经系统（CNS）中，包裹轴突的髓鞘受损或形成 在许多发育性脑障碍中是不正确的。因此，我们试图更好地了解控制 髓鞘形成以及它在这种情况下如何受损。基本上所有主要的髓鞘蛋白质都是 共价修饰的脂质棕榈酸酯，这一过程往往是关键的正确蛋白质亚细胞 定位和功能，但髓鞘蛋白棕榈酰化是如何控制的是未知的。因此，我们 X连锁智力残疾（XLID）基因ZDHHC 9编码一种特定的棕榈酰， 在少突胶质细胞（OL）（CNS的髓鞘形成细胞）中高度表达的酰基转移酶。 重要的是，具有Zdhhc 9功能丧失突变的人类患者和Zdhhc 9敲除（KO）小鼠表现出 认知缺陷，并显着减少前脑白色物质的体积，这表明一个关键作用， ZDHHC 9在OL形成和/或功能中的作用我们自己的研究表明，Zdhhc 9 KO小鼠的免疫功能受损， 胼胝体髓鞘形成而不损失神经元轴突和Zdhhc 9自主敲低细胞 在从培养物中的少突胶质前体细胞（OPC）分化后损害OL成熟。这些 引人注目的表型可能是导致人类患者智力残疾和/或癫痫发作的原因 ZDHHC 9突变。在这个项目中，我们将更精确地定义Zdhhc 9突变和 髓鞘形成障碍在目标1中，我们将结合联合收割机完善的电子显微镜（EM）和 免疫染色分析与遗传命运映射策略，以全面定义如何Zdhhc 9损失 影响体内OL分布和轴突髓鞘形成。在目标2中，我们将更精确地确定细胞如何- 自主性Zdhhc 9缺失影响OL分化和形态学加工。在每个目标中，我们将 比较ZDHHC 9的野生型（wt）和XLID突变体形式拯救观察到的表型的能力。 这些研究将提供新的见解，不仅是Zdhhc 9损失的影响，而且棕榈酰化- 髓鞘形成的依赖性控制，几十年前首次报道的过程，但几乎没有什么是 知道的因此，这项工作的见解对那些研究一系列大脑疾病的人来说是无价的，这些疾病的特点是： 白色物质损伤。

Abstract: The myelin sheaths that wrap around axons in the Central Nervous System (CNS) are damaged or formed incorrectly in many developmental brain disorders. We thus sought to better understand the control of myelination and how it may be impaired in such conditions. Essentially all of the major myelin proteins are covalently modified with the lipid palmitate, a process that is often critical for correct protein subcellular localization and function, but how myelin protein palmitoylation is controlled is unknown. We were therefore struck by findings that the X-linked Intellectual Disability (XLID) gene ZDHHC9 codes for a specific palmitoyl acyltransferase enzyme that is highly expressed in oligodendrocytes (OLs), the myelinating cells of the CNS. Importantly, human patients with ZDHHC9 loss-of-function mutations and Zdhhc9 knockout (KO) mice display cognitive deficits and have markedly reduced forebrain white matter volume, suggesting a key role for ZDHHC9 in OL formation and/or function. Our own studies revealed that Zdhhc9 KO mice have impaired corpus callosal myelination without loss of neuronal axons and that Zdhhc9 knockdown cell-autonomously impairs OL maturation after differentiation from Oligodendrocyte Precursor Cells (OPCs) in culture. These striking phenotypes may account for the intellectual disability and/or epileptic seizures seen in human patients with ZDHHC9 mutations. In this project we will more precisely define links between Zdhhc9 mutation and myelination impairments. In Aim 1, we will combine well-established Electron Microscopic (EM) and immunostaining analyses with a genetic fate-mapping strategy to comprehensively define how Zdhhc9 loss impacts OL distribution and axonal myelination in vivo. In Aim 2 we will more precisely determine how cell- autonomous Zdhhc9 loss affects OL differentiation and morphological elaboration. In each Aim we will compare the ability of wild type (wt) and XLID mutant forms of ZDHHC9 to rescue the observed phenotypes. These studies will provide new insights regarding not just the impact of Zdhhc9 loss, but also palmitoylation- dependent control of myelination, a process first reported decades ago but about which almost nothing is known. Insights from this work could thus be invaluable to those studying a range of brain disorders marked by White Matter Impairments.