Transcriptional Control of Dendritic Arbor Formation in the Mammalian Neocortex by Sip1

大脑皮层处理更高级的大脑功能，如决策和认知思维。组成新大脑皮层的主要神经元是锥体细胞，它们有精心分枝的、特定于神经元亚型的树突，其中包含专门的信息获取部位--树突。事实上，发育过程中树突枝的缺陷形成和成熟会导致神经元连接缺陷，并与许多人类神经发育障碍的认知障碍有关。我们的团队和其他人的工作已经开始识别直接启动分支和脊柱成熟的信号级联，但仍有许多尚不清楚。特别是对这些过程的转录调控，人们仍然知之甚少。转录因子SIP1(也称为ZFHX1b或ZEB2)的杂合突变已被证明会导致莫瓦特-威尔逊综合征，这是一种与严重智力残疾、多种先天性异常和癫痫有关的人类疾病。在这种情况下导致认知障碍的细胞和分子机制尚不清楚。我们的初步数据揭示了SIP1在哺乳动物新皮质发育过程中树突状突起形成中的一个新的关键作用。此外，我们的结果指出，SIP1至少在树突分枝的两个不同步骤中是必需的：获得极性和确定分支复杂性的程度。因此，本项目旨在研究SIP1在树突状分支和棘突的指定和形成中的作用，并进一步确定在哺乳动物新皮质发育过程中调节这些过程的下游信号机制。我们将通过宫内电穿孔在哺乳动物的新皮质中产生SIP1的马赛克删除，并将其与实时成像和免疫荧光染色相结合，以研究SIP1在树突分枝和成熟的每个步骤中的可能作用：从确定顶端树突到建立突触联系。此外，该项目将使用SIP1效应器突变、FACS分类的SIP1缺陷神经元的转录组深度测序和可用的微阵列数据来识别涉及的下游靶点。识别的靶点将在体内使用宫内电穿孔进行功能分析。我们希望借此加深我们对大脑皮层神经元网络形成的细胞和分子调控的理解，并为Mowat-Wilson病的认知障碍的发展提供见解。

The cerebral neocortex processes higher brain functions such as decision-making and cognitive thought. The principle neurons that make up the neocortex, the pyramidal cells, have elaborately branched, neuronal subtype-specific dendritic arbors that contain specialized sites for information acquisition, the dendritic spines. Indeed, defective formation and maturation of the dendritic arbor during development results in defective neuronal connectivity and is associated with cognitive impairment in a wide number of human neurodevelopmental disorders. Work by our group and others, has begun to identify the signaling cascades that direct initiation of branching and spine maturation, but much remains unclear. The transcriptional regulation of these processes in particular, is still poorly understood.Heterozygous mutations in the transcription factor Sip1 (also called ZFHX1b or ZEB2) have been shown to cause Mowat-Wilson syndrome, a human condition associated with severe intellectual disability, multiple congenital abnormalities and epilepsy. The cellular and molecular mechanisms that lead to impaired cognition in this condition are not known. Our preliminary data has revealed a novel critical role for Sip1 in the formation of the dendritic arbor during development of the mammalian neocortex. Moreover, our results point to a requirement for Sip1 in at least two distinct steps of dendritic arborisation: in the acquisition of polarity and in determining the extent of branching complexity. This project therefore aims to investigate the roles of Sip1 in the specification and formation of dendritic branches and spines and, furthermore, to identify the downstream signalling mechanisms that regulate these processes in the mammalian neocortex during development. We will generate mosaic deletion of Sip1 in the mammalian neocortex by in utero electroporation, and combine this with both live-imaging and immunofluorescent stainings to investigate the possible roles of Sip1 at each step of dendritic arborisation and maturation: from determination of the apical dendrite to the establishment of synaptic contact. Furthermore, the project will use Sip1 effector mutations, transcriptome Deep-Sequencing of FACS sorted Sip1-deficient neurons and available microarray data to identify the downstream targets involved. Identified targets will be functionally analysed in vivo using in utero electroporation. We intend thereby to further our understanding of the cellular and molecular regulation of neuronal network formation in the neocortex and provide insights to the development of cognitive impairment as occurs in Mowat-Wilson disease.