Rho GTPase signaling in the developing cerebral cortex

项目总结（见说明）： 在皮质发育过程中，神经元祖细胞增殖，然后从脑室区（VZ）迁移到皮质板（CP）中。这些未成熟细胞在离开VZ时采取以下两种路径之一：1）直接沿着放射状神经胶质支架迁移到CP，以由内而外的方式驻留，或者2）它们迁移到脑室下区（SVZ）并呈现多极形态以成为中间祖细胞（IP），在继续其前往CP的途中经历另一轮细胞分裂。虽然这些事件的中断已知有助于儿童神经发育 然而，对于神经源性疾病，调节祖细胞在独特的神经源性小生境中的保留和从其释放的因素还没有很好地理解。小RhoGTP酶，包括cdc42和RhoG，作为祖细胞增殖和发育中的皮质内的命运决定的调节剂。调节RhoGTP酶的机制，特别是在发育中的神经系统中，还没有很好地理解。这些由GEF和GAP组成的调节剂控制RhoGTP酶的GTP负载状态，从而控制RhoGTP酶的活性。由于GEFs作为RhoGTPases的激活剂，我们假设GEFs对RhoGTPases介导的祖细胞增殖调节和发育中大脑皮层的命运决定至关重要。我们试图确定在发育中的大脑皮层的神经原性壁龛中表达受限的GEFs。我们的努力使我们的小鸟嘌呤交换因子（SGEF），其表达仅限于VZ/SVZ在神经发生的高峰期。已知SGEF可诱导成纤维细胞和内皮细胞上富含F-肌动蛋白的突起的形成（1 - 2）。为了支持SGEF在发育中的大脑皮层中的作用，SGEF缺陷的小鼠（SGEF "）在SVZ中表现出减少的神经祖细胞增殖。我们将使用三个目标来验证我们的假设： 目的一：GEF表达的改变能否介导未成熟神经元行为的改变？ 目的II：GEFs是否选择性地影响神经祖细胞的增殖和定位？ 目的III：SGEF通过什么机制调节发育中的大脑皮层？ 这些研究旨在揭示GEFs在哺乳动物大脑皮层发育中的作用机制和功能调控。通过专注于SGEF，其表达仅限于发育中的大脑皮层中定义的神经原性小生境，其缺失似乎在中枢神经系统之外具有名义上的后果，我们能够使用发育中的大脑皮层作为模型来揭示GEFs如何调节RhoGT3信号传导的线索。'

PROJECT SUMMARY (See Instnjctions): During cortical development, neuronal progenitors proliferate and then migrate away from the ventricular zone (VZ) to take up residence in the cortical plate (CP). These immature cells take one of two paths upon exiting the VZ: 1) migrating directly along the radial glia scaffold to the CP, taking up residence in an inside out fashion or 2) they migrate to the subventricular zone (SVZ) and take on a multipolar morphology to become intermediate progenitors (IPs), undergo an additional round of cell division before continuing on their way to the CP. Although disruption in these events are known to contribute to pediatric neurodevelopmental disorders, the factors regulating progenitor retention in, and release from, unique neurogenic niches are not well understood. Small RhoGTPases, including cdc42 and RhoG, serve as regulators of progenitor proliferation and fate determination within the developing cortex. The mechanisms regulating RhoGTPases particularly in the developing nervous system, are not well understood. These regulators, comprised of GEFs and GAP) control the GTP-loading state, and thus activity, of RhoGTPases. Because GEFs act as activators for RhoGTPase, we hypothesize that GEFs are critical to RhoGTPase-mediated regulation of progenitor proliferation and fate determination in the developing cerebral cortex. We sought to identify GEFs with restricted expression in neurogenic niches of the developing cerebral cortex. Our efforts led us to a small guanine exchange factor (SGEF) whose expression is restricted to the VZ/SVZ during the peak of neurogenesis. SGEF is known to induce formation of F-actin rich protrusions on fibroblasts and endothelial cells (1-2). In support of a role for SGEF in the developing cerebral cortex, mice deficient in SGEF {SGEF^') exhibit reduced neural progenitor proliferation in the SVZ. We will use three aims to test our hypothesis: Aim I: Can altered GEF expression mediate changes in the behavior of immature neurons? Aim II: Do GEFs selectively influence the proliferation and placement of neural progenitors? Aim III: By what mechanism(s) does SGEF regulate the developing cerebral cortex? These studies seek to uncover the mechanism and functional regulation of GEFs in the development of the mammalian cerebral cortex. By focusing on SGEF, whose expression is restricted to a defined neurogenic niche in the developing cerebral cortex and whose deletion appears to have nominal consequences outside of the central nervous system, we are able to use the developing cerebral cortex as a model to uncover clues about how GEFs function to regulate RhoGTPase signaling. '