The Morphogen and Selector Gene Network in the Dorsal Telencephalic Midline

描述(申请人提供)：在发育过程中，在分开两个大脑皮层的背侧端脑中线(DTM)形成独特的组织。在这些组织中，包括皮质下层和脉络丛，前者是我们最近确定的海马区组织者，后者是脑脊液的来源。脉络丛是一种众所周知的组织，具有巨大的治疗潜力，但对其发育情况了解甚少。此外，DTM发育失败是无前脑畸形(HPE)的核心特征，HPE是人类前脑最常见的先天性畸形。本研究的目的是阐明控制DTM发育的机制和遗传网络，从而为HPE的发病机制和培养的脉络丛的产生提供临床应用的信息。以前的研究已经确定了骨形态发生蛋白(BMP)在DTM发育中的核心作用。例如，基因消融小鼠产生BMP的屋顶板会导致DTM诱导缺陷，而外源性Bmp4可以单独挽救这种缺陷。尽管如此，关于BMP信号和形态发生活性的基本问题仍然没有答案。遗传屋顶板消融还导致背侧形式的HPE，这导致了关于人类HPE患者的新发现，以及可以解释不同人类HPE表型产生的前脑发育信号网络模型。然而，在这个网络中，对BMP相互作用的洞察明显很差，包括识别抑制BMP途径以限制DTM命运和定位其边界的因素。我们以前使用顶板消融模型来研究BMPS在体内诱导DTM中的作用。最近，我们在培养的皮质神经前体细胞(NPC)中证明了与Bmp4作为DTM形态原的反应一致，并发现LIM同源结构域转录因子LHX2是一个皮质选择基因，可以抑制皮质HEM的命运。在初步研究中，我们将成纤维细胞生长因子8(FGF8)作为第二个DTM命运抑制因子，并描述了使能工具，包括新的BMP活性报告小鼠，微流控培养系统，以及DTM发育的数学模型。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的发病机制和脉络丛命运的指定之外，我们还可以解决形态形成生物学、发育边界形成和BMP活性调节等基本问题。在这项建议中，我们使用经过验证的体内、体外、微流体和硅胶工具来定义指导DTM发展的分子机制和遗传网络，重点是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管理端脑中线背侧区域发育的网络。这项提议是基于我们开发的一个信号网络模型，该模型可以解释无前脑畸形，这是人类前脑最常见的先天性畸形。该项目与公共卫生的相关性主要源于对这种常见出生缺陷的洞察，但也与与神经干细胞缺陷相关的精神和神经疾病的增加以及旨在治疗这些大脑疾病的NSC和其他干细胞策略有关。

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.