Regulation of neural development by TGF beta family signaling

描述（由申请人提供）：神经管的发育需要一系列复杂的形态学事件的协调，神经管缺陷是最常见的人类出生缺陷之一。通过Sonic Hedgehog （Shh）通路的信号调节发育中的前脑和神经管的背-腹侧模式。人类SHH基因突变会导致前脑全裂症（HPE），这是一种前脑发育的毁灭性遗传缺陷，每250个怀孕中就有1个，每10,000个活产婴儿中就有1.3个。多个位点的突变可导致HPE，并且观察到广泛的HPE表型，表明该疾病具有复杂的分子基础。Tgif1和Tgif2是通过Smad转录因子限制转化生长因子（TGF）信号传导的转录辅抑制因子。在HPE患者中发现了人类TGIF1基因突变，但TGIF1突变导致HPE的机制，以及TGIF1和TGF¿信号控制前脑和神经管发育的机制尚不清楚。我们通过在相关的Tgif2发生零突变的情况下，有条件地删除Tgif1，建立了Tgif功能完全丧失的小鼠模型。我们的数据表明，Tgif功能的缺失会破坏Shh信号，从而导致HPE。在缺乏TGF的情况下，通过TGF¿途径的过量信号传导阻止神经上皮细胞对Shh形态因子的反应，并增加Gli3的表达，从而进一步抑制Shh信号传导。我们建议测试TGF¿信号在神经发育过程中必须由转录辅抑制因子（如Tgif1和Tgif2）严格控制的模型。当这些控制存在缺陷时，过量的TGF¿信号激活整个神经管中的Gli3表达，并破坏神经上皮中的细胞极性，导致无法对Shh做出反应。为了验证该模型，我们将：1)验证TGF¿信号通过调节Shh通路维持背-腹侧神经管模式的假设。2)验证Smads直接激活Gli3基因表达控制神经管发育的假说。3)验证tgif通过调节细胞极性维持神经上皮对Shh的应答能力的假设。这项工作将确定TGF功能的丧失是否会通过破坏Shh通路导致HPE，并确定在神经管发育过程中限制TGF¿家族信号的重要性。此外，这项工作将确定TGF¿和Shh信号通路如何相互作用，并测试TGF¿信号通过控制细胞形态决定神经上皮对Shh反应能力的模型。

DESCRIPTION (provided by applicant): Neural tube development requires the coordination of a complex series of morphological events, and neural tube defects are among the most common human birth defects. Signaling via the Sonic Hedgehog (Shh) pathway regulates dorso-ventral patterning of the developing forebrain and neural tube. Mutations in the human SHH gene cause holoprosencephaly (HPE), a devastating genetic defect of forebrain development that affects 1 in 250 conceptions and 1.3 per 10,000 live births. Mutations at multiple loci can cause HPE, and a wide spectrum of HPE phenotypes is observed, suggesting a complex molecular basis for this disorder. Tgif1 and Tgif2 are transcriptional corepressors that limit Transforming Growth Factor (TGF) ¿ signaling via the Smad transcription factors. Mutations in the human TGIF1 gene are found in HPE patients, but the mechanisms by which TGIF1 mutations cause HPE, and by which Tgifs and TGF¿ signaling control forebrain and neural tube development are not known. We created a mouse model for complete loss of Tgif function by conditionally deleting Tgif1 in the context of null mutation in the related Tgif2. Our data suggest a model in which loss of Tgif function disrupts Shh signaling to cause HPE. In the absence of Tgifs, excess signaling via the TGF¿ pathway prevents the neuroepithelium from responding to the Shh morphogen, and increases expression of Gli3, which further inhibits Shh signaling. We propose to test the model that TGF¿ signaling must be tightly controlled during neural development by transcriptional corepressors, such as Tgif1 and Tgif2. When these controls are defective, excess TGF¿ signaling activates Gli3 expression throughout the neural tube, and disrupts cell polarity in the neuroepithelium resulting in an inability to respond to Shh To test this model, we will: 1) Test the hypothesis that Tgifs maintain dorso-ventral neural tube patterning by regulating the Shh pathway. 2) Test the hypothesis that Smads directly activate Gli3 gene expression to control neural tube development. 3) Test the hypothesis that by regulating cell polarity Tgifs maintain neuroepithelial competence to respond to Shh. This work will determine whether loss of Tgif function causes HPE by disrupting the Shh pathway, and determine the importance of limiting TGF¿ family signaling during neural tube development. Additionally this work will determine how the TGF¿ and Shh signaling pathways interact, and test the model that TGF¿ signaling determines the competence of the neuroepithelium to respond to Shh by controlling cell morphology. PUBLIC HEALTH RELEVANCE: Holoprosencephaly (HPE) is a devastating human genetic disease affecting forebrain and craniofacial development, which affects 1 in 250 conceptions, most resulting in miscarriage. The goal of this project is to understand the complex interactions of mutations that cause HPE, and to better understand normal forebrain development.