Novel non-cell autonomous mechanisms of callosal dysgenesis in CHARGE syndrome

摘要 胼胝体发育不全(CC)，连接大脑半球的大白质束， 发生在大约1：4000的人中，尤其是在3%-5%的发育性大脑障碍患者中 智力残疾或自闭症谱系障碍(ASD)。CC发育不全也存在于大约10%的 由杂合子引起的多发性发育异常--Charge综合征患者 CHD7的突变，它编码一个铬结构域解旋酶蛋白。重要的是，因为CC中的缺陷 只有通过尸检分析或结构磁共振才能确定发育情况，这在医学上是不可能的 在Charge综合征中，他们可能被严重低估。CC发育不全的贡献 充电综合症所特有的智力缺陷和自闭症行为尚不清楚。在……里面 在初步研究中，我发现了一种新的、高渗透性的CC发育不全表型。 综合征，推定的胼胝体轴突未能穿过中线，形成异常的Probst束和 被误送到隔膜。随后CHD7的条件性缺失表明CC发育不全 自主发展的非细胞，可能涉及CHD7单倍体不足的一个新的细胞群体通过 未知的机制。在其他的命运图研究中，我确定脉络丛和软脑膜是 在电荷模型中有两个可能导致CC发育不全的潜在组织。有趣的是，新兴的作品 建议脑膜，特别是软脑膜，是中线和胼胝体发育的关键控制者。 通过信号和与神经元的物理接触。然而，Pial的发展对CC的贡献 Charge综合征的发育不全和额外的轴突束缺陷从未被探索过。我的中央 假说认为，主症候群中的老茧发育不全是非细胞自主的结果。 软脑膜中线发育或功能缺陷。在这个提议中，我将通过(1)来检验这一假设 动物前脑中线群体发育所必需的胼胝体系统分析 电荷综合征模型。利用可用的鼠标行，我将(2)生成附加条件 CHD7基因缺失分析脑膜和脉络丛组织在CC中的潜在作用 表型。(3)分析软脑膜和脉络丛细胞转录水平的变化。 确定可能支持这一表型的下游基因。总而言之，这项工作是 预计将导致对未被探索的表型的机械性理解，这可能有助于关键 充电综合征表型的几个方面。这条科学追求的路线与我的 最终的职业目标是建立一个独立的研究项目，寻求一个实用和翻译的 了解发育性大脑疾病的遗传机制。正如培训中详细说明的那样 根据计划，拟议的工作将结合科学、技术和临床培训以及职业发展 机会，这将推动我的职业生涯，作为一名积极研究的临床科学家。

Abstract Agenesis of the corpus callosum (CC), the large white matter tract connecting the cerebral hemispheres, occurs in about 1:4000 individuals and in 3-5% of patients with a developmental brain disorder, in particular intellectual disability or autism spectrum disorder (ASD). CC agenesis is also present in approximately 10% of individuals with CHARGE syndrome, a multiple anomaly developmental disorder caused by heterozygous mutations in CHD7, which encodes a chromodomain helicase protein. Importantly, because defects in CC development can only be ascertained by post-mortem analysis or structural MRI, which is not medically indicated in CHARGE syndrome, they may be significantly under-diagnosed. The contribution of CC agenesis to the intellectual deficits and autistic behaviors characteristic of CHARGE syndrome remains unexplored. In preliminary studies, I identified a novel, highly-penetrant CC agenesis phenotype in a model of CHARGE syndrome, wherein presumptive callosal axons failed to cross the midline, formed aberrant Probst bundles and were misrouted to the septum. Subsequent conditional deletion of Chd7 suggested that CC agenesis developed non-cell autonomously, likely involving Chd7 haploinsufficiency in a novel cell population via an unexplored mechanism. In additional fate-mapping studies, I identified the choroid plexus and the pia mater as two potential tissues that can contribute to CC agenesis in the CHARGE model. Interestingly, emerging work has suggested the meninges, specifically the pia, to be a critical controller of midline and callosal development through signaling and physical contact with neurons. However, the contribution of pial development to the CC agenesis and additional axon tract defects in CHARGE syndrome has never been explored. My central hypothesis is that agenesis of the corpus callosum in CHARGE syndrome is the result of non-cell autonomous deficits in the development or function of the midline pia mater. In this proposal, I will test this hypothesis by (1) systematic analysis of the forebrain midline populations necessary for callosum development in the animal model of CHARGE syndrome. Leveraging available mouse lines, I will (2) generate additional conditional deletions of Chd7 to dissect the potential contribution of meningeal and choroid plexus tissue to the CC phenotype. And (3) I will analyze changes in the transcriptomes of pia mater and choroid plexus cells during callosal development to identify downstream genes that may underpin this phenotype. Together, this work is expected to lead to a mechanistic understanding of an underexplored phenotype that may contribute to key aspects of the CHARGE syndrome phenotype. This line of scientific pursuit is perfectly aligned with my ultimate career goal to establish an independent research program to seek a functional and translational understanding of the genetic mechanisms underlying developmental brain disorders. As detailed in the training plan, the proposed work will integrate scientific, technical, and clinical training, as well as career development opportunities, that will propel me towards a career as a clinician-scientist with active research.