Cellular and Molecular Mechanisms in Periventricular Heterotopia

描述（由申请人提供）：大脑皮层神经元迁移发育失败导致癫痫和智力迟钝。此外，神经发育障碍是一系列广泛的神经系统疾病的原因。定位克隆已经鉴定出脑室周围异位（PH）的人类基因突变，这是一种皮层发育畸形，其特征是在大脑皮层发育过程中，一部分神经元无法从脑室迁移。肌动蛋白结合丝蛋白A （FLNA）和囊泡运输相关的ARFGEF2这两个基因中的任何一个发生突变，都会导致神经元沿脑室内膜的初始迁移出现严重缺陷，并产生与人类PH几乎相同的放射学表现。小鼠体内纳帕基因的突变也会导致异位结节，与人类的异常相似。该应用的中心假设是，这些共同的突变表型是由编码蛋白之间的直接相互作用或共享的共同途径引起的。FLNA和ARFGEF2的功能似乎完全不同，因为FLNA与肌动蛋白细胞骨架和BIG2（由ARFGEF2编码）相互作用，通过鸟嘌呤交换调节adp核糖基化因子（ARFs）参与囊泡运输。在囊泡出芽的蛋白质外壳组装过程中需要ARF激活。α -SNAP（由Napa编码）是一种NSF附着蛋白，参与SNAP受体介导的囊泡融合。然而，总的来说，所有这些基因都参与了内体囊泡的运输，或者是通过调节运输所需的肌动蛋白丝、外壳蛋白的组装，或者是囊泡与膜的融合。因此，FLNA和ARFGEF2在引起PH中的作用可能与Napa通过控制内体囊泡运输具有共同的致病机制。因此，本研究的具体目的是确定：1)小鼠FLNA功能丧失后出现的哪些细胞缺陷有助于PH的形成，2)FLNA是否结合BIG2并指导BIG2定位和BIG2依赖性的ARF激活，以及3)神经祖细胞中Napa或ARFGEF2功能的丧失是否会改变导致PH形成的根尖和/或基底粘附连接。公共卫生相关性：已知几种基因的人类突变会导致几乎相同的脑畸形，并导致癫痫和智力迟钝。目前的建议旨在了解这些基因的细胞和分子机制，以及它们的功能如何在它们共同的表型下相互关联。了解人类大脑疾病的病理生理学为治疗干预的发展提供了一种手段。

DESCRIPTION (provided by applicant): Developmental failures in neuronal migration in the cerebral cortex result in epilepsy and mental retardation. Moreover, disorders in neural development account for a broad set of neurological diseases. Positional cloning has led to the identification of human genes mutated in periventricular heterotopia (PH), a malformation of cortical development characterized by the failure of a subset of neurons to migrate from the ventricle during cerebral cortical development. Mutations in either of two genes, the actin-binding filamin A (FLNA) and the vesicle transport related ARFGEF2, leads to severe defects in the initial migration of neurons along the ventricular lining and produces nearly identical radiographic findings of PH in humans. Mutations in the Napa gene in mice also lead to heterotopic nodules strikingly similar to those seen in humans. The central hypothesis of this application is that these common mutant phenotypes result from direct interactions between the encoded proteins or from a shared common pathway. The proposed functions of FLNA and ARFGEF2 appear quite disparate with FLNA implicated in neuronal motility due to its interactions with the actin cytoskeleton and BIG2 (encoded by ARFGEF2) involved in vesicle trafficking through its guanine exchange regulation of the ADP-ribosylation factors (ARFs). ARF activation is required during the assembly of protein coats for vesicle budding. Alpha-SNAP (encoded by Napa) is a NSF attachment protein, involved in SNAP receptor-mediated vesicle fusion. Collectively, however, all of these genes are involved in endosomal vesicle trafficking, either through regulation of actin filaments needed for transport, assembly of the coat protein, or fusion of the vesicle to the membrane. Thus, the role of FLNA and ARFGEF2 in giving rise to PH may share a common pathogenic mechanism with Napa by control over endosomal vesicle transport. Therefore the Specific Aims of this proposal are to determine: 1) which cellular defects seen following loss of FLNA function in mice contribute to PH formation, 2) whether FLNA binds BIG2 and directs BIG2 localization and BIG2-dependent ARF activation, and 3) whether loss of Napa or ARFGEF2 function in neural progenitors alters apical and/or basal adherens junctions leading to PH formation. PUBLIC HEALTH RELEVANCE: Human mutations in several genes are known to cause nearly identical brain malformations and result in epilepsy and mental retardation. The current proposal seeks to understand the cellular and molecular mechanisms of these genes, and how their function might be interrelated given their shared phenotype. Understanding the pathophysiology of human brain disorders provides a means for the development of therapeutic interventions.