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

摘要： 包裹在中枢神经系统(CNS)轴突周围的髓鞘受损或形成 在许多发育性大脑疾病中都是错误的。因此，我们试图更好地了解对 髓鞘形成以及在这种情况下髓鞘如何受损。基本上所有主要的髓鞘蛋白都是 用棕榈酸脂共价修饰，这一过程通常是正确的蛋白质亚细胞的关键 定位和功能，但如何控制髓鞘蛋白棕榈酸化是未知的。因此，我们 发现X连锁智力残疾(XLID)基因ZDHHC9编码一种特定的棕榈酸酯 一种在少突胶质细胞中高表达的酰基转移酶，少突胶质细胞是中枢神经系统的髓鞘细胞。 重要的是，人类ZDHHC9功能丧失突变患者和Zdhhc9基因敲除(KO)小鼠显示 认知障碍，并显著减少前脑白质体积，表明 ZDHHC9在OL形成和/或功能中的作用我们自己的研究表明，Zdhc9 KO小鼠已经损害了 无神经元轴突丢失的穹隆体髓鞘形成和Zdhhc9基因敲除细胞--自主 在培养中从少突胶质前体细胞(OPC)分化为OL后损害OL的成熟。这些 显著的表型可能是人类患者智力残疾和/或癫痫发作的原因 ZDHHC9基因突变。在这个项目中，我们将更精确地定义Zdhhc9突变和 髓鞘损伤。在目标1中，我们将结合成熟的电子显微镜(EM)和 用遗传命运图策略进行免疫染色分析以全面确定Zdhhc9丢失的原因 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- 自主的Zdhhc9缺失影响OL的分化和形态的细化。在每个目标中，我们都会 比较ZDHHC9野生型(Wt)和XLID突变型对观察到的表型的挽救能力。 这些研究将提供新的见解，不仅关于Zdhhc9丢失的影响，而且还包括棕榈酰化- 依赖控制髓鞘形成，这一过程几十年前首次报道，但几乎没有关于它的报道 为人所知。因此，这项工作的洞察力对那些研究一系列大脑疾病的人来说可能是无价的。 脑白质损伤。

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.