Regulation of neural development by TGF beta family signaling

描述（申请人提供）：神经管发育需要一系列复杂形态事件的协调，神经管缺陷是人类最常见的出生缺陷之一。通过Sonic Hedgehog（Shh）通路的信号传导调节发育中的前脑和神经管的背腹模式。人类SHH基因的突变会导致前脑无裂畸形（HPE），这是一种前脑发育的毁灭性遗传缺陷，每250次受孕中就有1次，每10，000次活产中就有1.3次。多个位点的突变可导致HPE，并且观察到广泛的HPE表型，表明这种疾病的复杂分子基础。Tgif1和Tgif2是转录辅抑制因子，通过Smad转录因子限制转化生长因子（TGF）信号传导。在HPE患者中发现了人类TGIF1基因的突变，但TGIF1突变导致HPE的机制以及Tgif和TGF β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Tgif 2中的无效突变的背景下有条件地删除Tgif 1来创建Tgif功能完全丧失的小鼠模型。我们的数据提出了一个模型，其中Tgif功能的丧失会扰乱Shh信号传导，从而导致HPE。在没有Tgifs的情况下，通过TGF β通路的过量信号传导阻止神经上皮对Shh形态原的响应，并增加Gli3的表达，这进一步抑制Shh信号传导。我们建议测试的模型，TGF β信号必须严格控制在神经发育过程中的转录辅阻遏物，如Tgif 1和Tgif 2。当这些控制有缺陷时，过量的TGF β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作出反应。为了测试该模型，我们将：1）测试Tgif通过调节Shh通路维持背腹神经管模式的假设。2)验证Smads直接激活Gli3基因表达以控制神经管发育的假设。3)测试Tgifs通过调节细胞极性来维持神经上皮对Shh反应的能力的假设。 这项工作将确定Tgif功能的丧失是否通过破坏Shh通路导致HPE，并确定在神经管发育期间限制TGF β家族信号传导的重要性。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？信号通路通过控制细胞形态决定神经上皮对Shh反应的能力的模型。

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.