Nf2-dependent regulation of neuronal scaling in the developing cerebellum

总结 不同类型的神经元以适当的比例产生，称为神经元缩放，是至关重要的 形成功能性神经回路和适当的兴奋/抑制平衡。神经元破坏 结垢有助于发育性脑疾病的发病机制，包括脊髓小脑共济失调， 自闭症虽然在理解特定的细胞分化方面取得了重大进展， 神经元，很少有人知道的机制，规模的功能相关的神经元的数量在 个脑袋小脑只包含少数神经元细胞类型，其发育起源是很好的- 确立了习因此，小脑是研究神经元缩放机制的理想系统。在 小脑，菱形唇源性兴奋颗粒神经元和室带源性抑制颗粒神经元 中间神经元相对于浦肯野细胞缩放，浦肯野细胞是来自小脑皮质的唯一输出神经元。Purkinje 细胞通过分泌Sonic hedgehog（Shh）蛋白来控制颗粒细胞的数量， 颗粒细胞前体的增殖和前体细胞在预期的白色物质（pWM）中的扩增 从而产生抑制性中间神经元。在迁移到pWM之前，神经祖细胞在 小脑脑室区（cVZ），其也产生浦肯野细胞层祖细胞（PCLP），其在 正常发育只产生神经胶质。虽然浦肯野细胞产生Shh和Shh转导在 颗粒细胞前体已经被深入研究，神经元缩放机制，内在地作用于 cVZ衍生的细胞知之甚少。在我们的初步研究中，我们发现， 神经纤维瘤病2（Nf 2）基因导致一种独特的表型， 抑制性中间神经元相对于浦肯野细胞。令人兴奋的是，我们在小鼠中的条件敲除分析显示， Nf 2控制小脑中的神经元缩放，内在地作用于cVZ衍生的细胞，以调节几个神经元的功能。 明显的，不为人知的发育步骤。该提案将描述分子机制 在三个互补的目标中，使用Nf 2作为切入点，调节小脑中的神经元缩放。在 目的1，我们将研究Nf 2如何协调cVZ中祖细胞的增殖和迁移， 鉴定调节这些过程中的每一个的新的Nf 2下游靶标。在目标2中，我们将定义一个 调节pWM祖细胞对Shh的扩增和增殖反应的Nf 2依赖性途径。在 目的3，我们将确定Nf 2依赖的机制，抑制PCLPs误指定为颗粒细胞， 防止在正常发育过程中产生过多的颗粒细胞。我们的研究将确定基本的 调节小脑发育的机制，小脑是运动协调和认知的主要中心 功能，将为人类小脑发育障碍提供新的见解，并有助于发展 大脑再生疗法。

Summary The production of different types of neurons in the appropriate proportions, called neuronal scaling, is critical for the formation of functional neural circuits and proper excitatory/inhibitory balance. Disruption of neuronal scaling contributes to the pathogenesis of developmental brain disorders, including spinocerebellar ataxia and autism. Although significant progress has been made toward understanding the differentiation of specific neurons, little is known regarding the mechanisms that scale the number of functionally related neurons in the brain. The cerebellum contains only few neuronal cell types, the developmental origins of which are well- established. Thus, the cerebellum is an ideal system to study the mechanisms of neuronal scaling. In the cerebellum, both rhombic lip-derived excitatory granule neurons and ventricular zone-derived inhibitory interneurons are scaled relative to Purkinje cells, the only output neurons from the cerebellar cortex. Purkinje cells control the number of granule cells by secreting the Sonic hedgehog (Shh) protein, which promotes the proliferation of granule cell precursors and the expansion of progenitors in the prospective white matter (pWM) that give rise to inhibitory interneurons. Before migrating to the pWM, neural progenitors proliferate in the cerebellar ventricular zone (cVZ), which also gives rise to Purkinje cell layer progenitors (PCLPs), which during normal development produce exclusively glia. While Shh production by Purkinje cells and Shh transduction in granule cell precursors has been studied intensively, the neuronal scaling mechanisms that act intrinsically in cVZ-derived cells are poorly understood. In our preliminary studies, we found that loss of the Neurofibromatosis 2 (Nf2) gene results in a unique phenotype with disrupted scaling of both granule cells and inhibitory interneurons relative to Purkinje cells. Excitingly, our conditional knockout analysis in mice revealed that Nf2 controls neuronal scaling in the cerebellum acting intrinsically in cVZ-derived cells to regulate several distinct, poorly understood developmental steps. This proposal will characterize the molecular mechanisms that regulate neuronal scaling in the cerebellum, using Nf2 as an entry point, in three complementary Aims. In Aim 1, we will investigate how Nf2 coordinates the proliferation and migration of progenitors in the cVZ, identifying novel Nf2 downstream targets that regulate each of these processes. In Aim 2, we will define an Nf2-dependent pathway that regulates the expansion and proliferative response to Shh of pWM progenitors. In Aim 3, we will identify Nf2-dependent mechanisms that inhibit the misspecification of PCLPs into granule cells, preventing the production of excessive granule cells during normal development. Our studies will identify basic mechanisms that regulate development of the cerebellum, a major center of motor coordination and cognitive functions, will provide novel insights into human cerebellar developmental disorders, and help the development of brain regeneration therapies.