TGF beta regulation of cilium-dependent signaling

描述（由申请人提供）：初级纤毛在细胞信号传导和哺乳动物发育中起重要作用。纤毛缺陷与许多人类发育障碍有关，包括脑积水、慢性肺阻塞、多囊肾病和左右不对称缺陷。初级纤毛对于Sonic hedgehog（Shh）信号传导至关重要，并且可能在其他信号传导途径中发挥作用。破坏Shh信号传导或纤毛功能的突变在小鼠中引起相似的表型，包括肢体缺陷和前脑无裂畸形（HPE），这是一种影响颅面发育的严重遗传疾病。编码Shh和Tgif 1的人类基因中的功能缺失突变与HPE相关。Tgif 1是一种转录辅抑制因子，通过Smad 2限制转化生长因子（TGF）信号传导。然而，目前尚不清楚Tgif 1和相关的Tgif 2如何调节胚胎发生，或Tgifs和TGF信号如何调节纤毛发生和Shh信号。 我们建议测试的模型，TGF家族信号必须严格限制在胚胎发育过程中，和无限制的TGF家族信号通过Smad 2破坏细胞极性和初级纤毛的形成，从而抑制纤毛依赖性信号。通过在小鼠中有条件地靶向Tgif 1和Tgif 2基因，我们已经创建了一个小鼠模型，用于过量的TGF信号传导，其中细胞极性和纤毛发生被破坏。此外，缺乏所有Tgif功能的小鼠具有胚胎缺陷，包括HPE和左右不对称缺陷，并且具有多能性因子Nanog的表达增加。 具体而言，我们将：1）确定Tgif是否通过经由Smad 2抑制TGF/Nodal信号传导来控制前脑中的Shh信号传导，并测试在Tgif不存在下的HPE是否是由于过量的TGF家族信号传导。2)确定在Tgif功能缺失的情况下，前脑是否由于极性缺陷和初级纤毛缺失而无法对Shh信号传导做出反应，或者Tgif和TGF信号传导是否直接调节Shh基因表达。3)确定是否必须限制TGF家族信号传导，以防止其他胚胎组织（包括神经管和淋巴结）中初级纤毛和纤毛依赖性信号传导的破坏。最后，我们将测试Nanog是否是Tgif抑制的直接靶点，以及过量Nanog表达是否会导致细胞极性和纤毛发生缺陷。这项工作将确定Tgifs和TGF信号传导如何与Shh通路整合，并确定TGF信号传导在纤毛发生和纤毛依赖性信号传导中的作用。

DESCRIPTION (provided by applicant): The primary cilium plays important roles in cellular signaling and mammalian development. Cilia defects are associated with a number of human developmental disorders, including hydrocephaly, chronic pulmonary obstruction, polycystic kidney disease and left-right asymmetry defects. Primary cilia are critical for Sonic hedgehog (Shh) signaling, and may play roles in other signaling pathways. Mutations that disrupt Shh signaling or cilia function cause similar phenotypes in mice, including limb defects and holoprosencephaly (HPE), a severe genetic disorder affecting craniofacial development. Loss of function mutations in the human genes encoding Shh and Tgif1 are associated with HPE. Tgif1 is a transcriptional corepressor that limits transforming growth factor (TGF) signaling via Smad2. However, it is not known how Tgif1, and the related Tgif2, regulate embryogenesis, or how Tgifs and TGF signaling regulate ciliogenesis and Shh signaling. We propose to test the model that TGF family signaling must be strictly limited during embryonic development, and that unrestrained TGF family signaling via Smad2 disrupts cell polarity and the formation of primary cilia, thereby inhibiting cilia-dependent signaling. By conditionally targeting both the Tgif1 and Tgif2 genes in mice, we have created a mouse model for excess TGF signaling, in which cell polarity and ciliogenesis are disrupted. Additionally, mice lacking all Tgif function have embryonic defects, including HPE and left-right asymmetry defects, and have increased expression of the pluripotency factor, Nanog. Specifically, we will: 1) Determine whether Tgifs control Shh signaling in the forebrain by restraining TGF/Nodal signaling via Smad2, and test whether HPE in the absence of Tgifs is due to excess TGF family signaling. 2) Determine whether, in the absence of Tgif function, the forebrain is unable to respond to Shh signaling due to polarity defects and the absence of primary cilia, or whether Tgifs and TGF signaling directly regulate Shh gene expression. 3) Determine whether TGF family signaling must be limited to prevent disruption of primary cilia and cilia- dependent signaling in other embryonic tissues, including the neural tube and node. Finally, we will test whether Nanog is a direct target for repression by Tgifs, and whether excess Nanog expression causes the cell polarity and ciliogenesis defects. This work will determine how Tgifs and TGF signaling are integrated with the Shh pathway, and determine the role that TGF signaling plays in ciliogenesis and cilia-dependent signaling.