The Morphogen and Selector Gene Network in the Dorsal Telencephalic Midline

描述（由申请人提供）：在发育过程中，分离两个大脑皮层的背端脑中线（DTM）形成独特的组织。在这些组织中有皮质边缘，我们最近发现它是海马的组织者，脉络丛，脑脊液（CSF）的来源。脉络膜丛是一种众所周知的具有显著治疗潜力的组织，但其发展却知之甚少。此外，DTM发育失败是人类前脑最常见的先天性畸形——全前脑畸形（HPE）的核心特征。本研究的目的是阐明DTM发展的机制和遗传网络，这将为HPE的发病机制和脉络膜丛的产生提供信息，以供临床应用。先前的研究已经确定了骨形态发生蛋白（Bmps）在DTM发育中的核心作用。例如，小鼠产生bmp的顶板的基因消融导致DTM诱导缺陷，可以通过外源性Bmp4单独挽救。尽管如此，关于Bmp信号和形态发生活动的基本问题仍然没有答案。基因顶板消融也会导致背侧HPE，这导致了关于人类HPE患者和前脑发育信号网络模型的新发现，该模型可以解释不同人类HPE表型的产生。然而，在这个网络中，对Bmp相互作用的了解非常少，包括抑制Bmp通路以限制DTM命运和定位其边界的因素的识别。我们之前使用屋顶板消融模型来暗示Bmps在体内DTM诱导中的作用。最近，我们在培养的皮质神经前体细胞（NPCs）中证实了Bmp4作为DTM形态因子的反应，并确定了LIM同位结构域转录因子Lhx2作为皮质选择基因抑制皮质下丘脑命运。在初步研究中，我们暗示成纤维细胞生长因子8 （Fgf8）是第二个DTM命运抑制因子，并描述了实现工具，包括新的Bmp活性报告小鼠，微流体培养系统和DTM发展的数学模型。这些发现和工具为我们提供了一个独特的机会，在脊椎动物中枢神经系统模型系统中，除了HPE发病机制和脉络膜丛命运规范外，还可以解决形态发生生物学、发育边界形成和Bmp活性调节等基本问题。在本提案中，我们使用经过验证的体内、体外、微流体和硅工具来定义指导DTM发展的分子机制和遗传网络，重点关注Bmp活性和调节它的因素。公共卫生相关性：该项目的目标是更好地了解控制端脑背中线区域发育的网络。该建议是基于我们开发的信号网络模型，该模型可以解释人类前脑最常见的先天性畸形——前脑全裂畸形。该项目与公共卫生的相关性主要来自对这种常见出生缺陷的深入了解，也来自与神经干细胞缺陷相关的越来越多的精神和神经疾病，以及旨在治疗这些脑部疾病的NSC和其他干细胞战略。

DESCRIPTION (provided by applicant): During development, distinctive tissues form in the dorsal telencephalic midline (DTM) that separates the two cerebral cortices. Among these tissues are the cortical hem, which we recently identified as being a hippocampal organizer, and the choroid plexus, the source of cerebrospinal fluid (CSF). The choroid plexus is a well-known tissue with significant therapeutic potential, but its development is quite poorly understood. Moreover, failed DTM development is a central feature of holoprosencephaly (HPE), the most common congenital malformation of the human forebrain. The goal of this proposal is to elucidate the mechanisms and genetic network that govern DTM development, which will inform HPE pathogenesis and the generation of choroid plexus in culture for clinical applications. Previous studies have established central roles for the bone morphogenetic proteins (Bmps) in DTM development. For example, genetic ablation of the Bmp-producing roof plate in mice causes DTM induction deficits that can be rescued with exogenous Bmp4 alone. Nonetheless, fundamental questions about Bmp signaling and morphogenic activity remain unanswered. Genetic roof plate ablation also causes a dorsal form of HPE, which led to new discoveries about human HPE patients and a signaling network model of forebrain development that can explain how distinct human HPE phenotypes arise. However, within this network, insights into Bmp interactions are notably poor, including the identity of factors that inhibit the Bmp pathway to restrict DTM fates and position their borders. We previously used the roof plate ablation model to implicate Bmps in DTM induction in vivo. More recently, we demonstrated responses in cultured cortical neural precursor cells (NPCs) consistent with Bmp4 acting as a DTM morphogen, and identified the LIM homeodomain transcription factor Lhx2 as a cortical selector gene that suppresses cortical hem fate. In Preliminary Studies, we implicate fibroblast growth factor 8 (Fgf8) as a second DTM fate suppressor and describe enabling tools that include a new Bmp activity reporter mouse, a microfluidic culture system, and a mathematical model of DTM development. These findings and tools provide us with a unique opportunity, among vertebrate CNS model systems, to address fundamental questions in morphogen biology, developmental border formation, and Bmp activity regulation in addition to HPE pathogenesis and choroid plexus fate specification. In this proposal, we use validated in vivo, in vitro, microfluidic, and in silico tools to define the molecular mechanisms and genetic network that direct DTM development, focusing on Bmp activity and the factors that modulate it. PUBLIC HEALTH RELEVANCE: The goal for this project is to better understand the network that governs development of the dorsal midline region in the telencephalon. The proposal is based on a signaling network model we developed that can explain holoprosencephaly, the most common congenital malformation of the human forebrain. The relevance of this project to public health derive mainly from the insights into this common birth defects, but also to the increasing number of psychiatric and neurologic diseases associated with neural stem cell defects, and to NSC and other stem cell strategies aimed at treating these brain disorders.