Regulation of Placental and Embryonic Development by Tgifs

描述(申请人提供)：哺乳动物胎盘提供了一个很大的表面积，母亲和胚胎之间的营养和气体交换发生在这个表面积上。胎盘功能不全导致胎儿宫内发育迟缓(IUGR)，是围产儿死亡的第二大原因，影响高达6%的人类妊娠。小鼠和人类胎盘之间有显著的功能保守，许多关键的调节因子在两个物种之间也是保守的。滋养层干细胞是小鼠胎盘所有主要细胞类型的来源，正确的TS细胞分化是胎盘正常发育所必需的。维甲酸(RA)和Nodal信号对TS细胞的分化有相反的作用：RA信号促进滋养层巨细胞的形成而损害海绵状滋养层细胞的形成，而Nodal则减少巨细胞的形成。这两条途径中的任何一条都会导致胎盘发育异常。胸腺嘧啶鸟嘌呤相互作用因子(TGIF)是一种转录辅阻遏子，可限制转化生长因子β/结节和类风湿因子信号转导。TGIF招募一般的辅抑制子来激活Smads，限制了转化生长因子β/Nodal转录激活的程度。TGIF与RXR维甲酸受体相互作用，抑制RA依赖基因的表达。在小鼠中，TGIF零突变会导致胎盘缺陷，而缺乏TGIF和功能相关的Tgif2的胚胎在原肠形成后不久就会死亡。我们将验证这样一个假设，即TGIF在不同发育阶段的Nodal和RA信号转导中具有关键功能：TGIF和Tgif2功能的完全丧失会导致原肠发育缺陷，主要是通过下调Nodal调控的基因表达。在发育后期，RA信号对TGIF功能降低很敏感，RA反应转录的抑制会导致TS细胞分化和胎盘发育的缺陷。我们将测试TGIF突变是否会改变RA和Nodal信号，从而导致胎盘发育缺陷。我们将测试TGIF是否在体外通过抑制TS细胞对RA和Nodal的转录反应来调节TS细胞的分化。最后，我们将测试TGIF和Tgif2功能的完全丧失是否会导致原肠发育缺陷，方法是抑制Nodal激活的基因表达，从而导致增殖减少和轴形成缺陷。这将决定TGIF如何调控胎盘和胚胎发育，并对胎盘功能不全、胚胎发育和宫内发育迟缓有更好的理解。

DESCRIPTION (provided by applicant): The mammalian placenta provides a large surface area over which exchange of nutrients and gases between the mother and embryo occurs. Placental insufficiency results in intrauterine growth retardation (IUGR), which is the second leading cause of perinatal death, affecting up to 6% of human pregnancies. There is significant conservation of function between mouse and human placenta, and many of the key regulators are also conserved between the two species. Trophoblast stem (TS) cells give rise to all major cell types of the mouse placenta, and correct TS cell differentiation is required for normal placental development. Retinoic acid (RA) and Nodal signaling have opposing effects on TS cell differentiation: RA signaling promotes the formation of trophoblast giant cells at the expense of spongiotrophoblasts, whereas, Nodal decreases giant cell formation. Disruption of either pathway results in aberrant placental development. Tgif (Thymine Guanine Interacting Factor) is a transcriptional corepressor, which limits both TGF beta/Nodal and RA signaling. Tgif recruits general corepressors to activated Smads, limiting the extent of transcriptional activation by TGF beta/Nodal. Tgif interacts with the RXR retinoic acid receptor and represses RA dependent gene expression. A Tgif null mutation in mice causes placental defects, whereas embryos lacking both Tgif and the functionally related Tgif2 die soon after gastrulation. We will test the hypothesis that Tgifs have critical functions in Nodal and RA signaling at different developmental stages: Complete loss of Tgif and Tgif2 function causes gastrulation defects, primarily by derepressing Nodal regulated gene expression. Later in development, RA signaling is sensitive to reduced Tgif function, and derepression of RA-responsive transcription causes defects in TS cell differentiation and placental development. We will test whether the Tgif mutation alters RA and Nodal signaling, causing defects in placental development. We will test whether Tgif regulates TS cell differentiation in vitro by repressing the transcriptional response of TS cells to RA and Nodal. Finally, we will test whether complete loss of Tgif and Tgif2 function causes defects in gastrulation, by derepressing Nodal-activated gene expression resulting in decreased proliferation and defective axis formation. This will determine how Tgifs regulate placental and embryonic development and generate a better understanding of placental insufficiency, embryonic development and intrauterine growth retardation.