Cellular and Molecular Mechanisms in Periventricular Heterotopia

描述(申请人提供)：大脑皮层神经元迁移的发育障碍会导致癫痫和智力低下。此外，神经发育障碍是导致一系列神经疾病的主要原因。定位克隆导致了在脑室周围异位症(PH)中发现了突变的人类基因，PH是一种皮质发育的畸形，其特征是在大脑皮质发育过程中，部分神经元无法从脑室迁移出来。肌动蛋白结合细丝蛋白A(Flna)和与囊泡运输相关的ARFGEF2基因中的任何一个基因的突变，都会导致神经元沿着脑室内壁的初始迁移出现严重缺陷，并产生与人类PH几乎相同的放射学结果。小鼠的NapA基因突变也会导致异位结节，与人类的异位结节惊人地相似。这一应用的中心假设是，这些常见的突变表型是编码蛋白之间直接相互作用的结果，或者是来自共同的共同途径。由于其与肌动蛋白细胞骨架的相互作用，以及由ARFGEF2编码的BIG2(由ARFGEF2编码)通过其对ADP-核糖化因子(ARF)的鸟嘌呤交换调节而参与囊泡运输，因此，所提出的FLNA和ARFGEF2的功能似乎与参与神经元运动的FLNA截然不同。在囊泡萌发的蛋白质涂层组装过程中，ARF激活是必需的。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，要么是通过调节运输所需的肌动蛋白细丝，要么是通过组装外壳蛋白，或者是通过将囊泡融合到膜上。因此，FLNA和ARFGEF2在PH发生中的作用可能与NAPA具有共同的致病机制，即控制内体小泡运输。因此，这项建议的具体目的是确定：1)在小鼠中，Flna功能丧失后出现的哪些细胞缺陷有助于PH的形成；2)Flna是否与BIG2结合并指导BIG2定位和BIG2依赖的ARF激活；3)神经前体细胞中NapA或ARFGEF2功能的丧失是否改变了导致PH形成的心尖和/或基底黏附连接。

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.