TGF beta regulation of cilium-dependent signaling

描述(申请人提供)：初级纤毛在细胞信号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、慢性肺梗阻、多囊肾病和左右不对称缺陷。初生纤毛在Sonic hedgehog(Shh)信号转导中起关键作用，也可能在其他信号转导途径中发挥作用。破坏Shh信号或纤毛功能的突变会在小鼠中引起类似的表型，包括肢体缺陷和无前脑畸形(HPE)，这是一种严重的遗传疾病，影响头面部发育。编码Shh和Tgif1的人类基因功能缺失突变与HPE有关。Tgif1是一种转录抑制因子，通过Smad2限制转化生长因子(TGF)信号传导。然而，目前尚不清楚Tgif1及其相关的Tgif2是如何调控胚胎发育的，也不知道TGIFs和转化生长因子信号如何调控纤毛发生和Shh信号。我们建议验证这样的模型，即在胚胎发育过程中必须严格限制转化生长因子家族信号，而不受抑制的转化生长因子家族信号通过Smad2干扰细胞极性和初生纤毛的形成，从而抑制纤毛依赖的信号转导。通过有条件地针对小鼠的Tgif1和Tgif2基因，我们创建了一个过度转化生长因子信号的小鼠模型，在该模型中，细胞极性和纤毛发生被破坏。此外，缺乏所有TGIF功能的小鼠存在胚胎缺陷，包括HPE和左右不对称缺陷，并增加了多能性因子Nanog的表达。具体地说，我们将：1)确定TGIF是否通过Smad2抑制TGF/Nodal信号来控制前脑中的Shh信号，并测试在没有TGIF的情况下HPE是否由于过度的TGF家族信号所致。2)确定在缺乏TGIF功能的情况下，前脑是否由于极性缺陷和初级纤毛的缺失而不能对Shh信号做出反应，或者TGIF和TGF信号是否直接调节Shh基因的表达。3)确定是否必须限制转化生长因子家族信号，以防止初级纤毛和其他胚胎组织(包括神经管和结节)纤毛依赖信号的中断。最后，我们将测试Nanog是否是TGIF抑制的直接靶点，以及过度表达Nanog是否会导致细胞极性和纤毛发生缺陷。这项工作将确定TGIF和转化生长因子信号如何与Shh途径整合，并确定转化生长因子信号在纤毛发生和纤毛依赖信号中所起的作用。

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.