Cellular and Molecular Mechanisms in Periventricular Heterotopia

描述（由申请人提供）：大脑皮层神经元迁移的发育失败导致癫痫和智力迟钝。此外，神经发育障碍导致了一系列广泛的神经系统疾病。定位克隆已导致鉴定出在脑室周围异位（PH）中突变的人类基因，PH是一种皮质发育畸形，其特征在于在大脑皮质发育期间神经元子集从脑室迁移的失败。肌动蛋白结合细丝蛋白A（FLNA）和囊泡转运相关的ARFGEF 2两种基因中的任何一种突变都会导致神经元沿心室衬里沿着的初始迁移严重缺陷，并产生与人类PH几乎相同的放射学结果。小鼠Napa基因的突变也会导致异位结节，这与人类的异常相似。本申请的中心假设是，这些共同的突变体表型是由编码的蛋白质之间的直接相互作用或由共享的共同途径引起的。FLNA和ARFGEF 2的拟议功能似乎完全不同，FLNA与神经元运动有关，因为它与肌动蛋白细胞骨架和BIG 2（由ARFGEF 2编码）相互作用，BIG 2通过ADP-核糖基化因子（ARF）的鸟嘌呤交换调节参与囊泡运输。ARF活化是在蛋白质外壳组装过程中为囊泡出芽所必需的。α-SNAP（由Napa编码）是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，无论是通过调节运输所需的肌动蛋白丝，外壳蛋白的组装，还是囊泡与膜的融合。因此，FLNA和ARFGEF 2在引起PH中的作用可能与Napa通过控制内体囊泡转运而具有共同的致病机制。因此，本提案的具体目的是确定：1）在小鼠中FLNA功能丧失后观察到的哪些细胞缺陷有助于PH形成，2）FLNA是否结合BIG 2并指导BIG 2定位和BIG 2依赖性ARF激活，以及3）神经祖细胞中Napa或ARFGEF 2功能丧失是否改变导致PH形成的顶端和/或基底粘附连接。

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.