Regulation of neural development by TGF beta family signaling

描述(申请人提供)：神经管的发育需要一系列复杂的形态事件的协调，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模式。人类SHH基因的突变会导致全前脑(HPE)，这是一种前脑发育的毁灭性遗传缺陷，每250个妊娠中就有1个受到影响，每10,000个活产中就有1.3个受到影响。多个基因座的突变可引起HPE，并观察到广泛的HPE表型，提示这种疾病有复杂的分子基础。Tgif1和Tgif2是转录共抑制因子，通过Smad转录因子限制转化生长因子信号转导。人类TGIF1基因突变在HPE患者中被发现，但TGIF1突变导致HPE的机制以及TGIF和转化生长因子β信号控制前脑和神经管发育的机制尚不清楚。我们通过有条件地在相关Tgif2零突变的情况下删除Tgif1，建立了一种TGIF功能完全丧失的小鼠模型。我们的数据提出了一种模型，在该模型中，TGIF功能的丧失扰乱了Shh信号，从而导致HPE。在缺乏TGIF的情况下，通过转化生长因子途径的过度信号会阻止神经上皮细胞对Shh形态原的反应，并增加Gli3的表达，从而进一步抑制Shh信号。我们建议测试这一模型，即在神经发育过程中，转化生长因子信号必须通过转录辅助抑制物，如Tgif1和Tgif2来严格控制。当这些对照有缺陷时，过量的转化生长因子信号激活整个神经管中Gli3的表达，扰乱神经上皮细胞的极性，导致无法对Shh做出反应。为了测试这个模型，我们将：1)测试TGIF通过调节Shh途径维持背-腹侧神经管模式的假设。2)验证Smads直接激活Gli3基因表达以控制神经管发育的假设。3)验证TGIF通过调节细胞极性来维持神经上皮细胞对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扰乱Shh途径而导致HPE，并确定限制转化生长因子家族信号在神经管发育中的重要性。此外，这项工作将确定转化生长因子β和Shh信号通路如何相互作用，并测试转化生长因子β信号通过控制细胞形态决定神经上皮对Shh反应的能力的模型。 公共卫生相关性：无前脑畸形(HPE)是一种毁灭性的人类遗传病，影响前脑和颅面发育，每250个妊娠中就有1个受到影响，大多数导致流产。这个项目的目标是了解导致HPE的突变的复杂相互作用，并更好地了解正常的前脑发育。

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.