Studies on the establishment of the primitive streak region

体轴的后向延伸是通过在由节点和原始条纹组成的原始条纹区域中依次添加更多的后向组织来实现的。我们之前发现Foxa2基因的节点/脊索增强子的核心元件在原始条纹区特异性地驱动基因表达。因此，为了解决原始条纹区建立的机制，我们分析了核心元素的调控机制。核心元件在Wnt/β-catenin处理的P19细胞中被激活，这种激活依赖于两个转录因子的结合位点。这些结合位点对于淋巴结/脊索增强子的体内活性也是必不可少的。其中一种增强子结合蛋白是Tead， Tead- enr在转基因小鼠胚胎中抑制Tead活性导致脊索缺失。斑马鱼胚胎中Tead活性的调节也改变了胚胎盾中foxa2的表达。这些发现表明，Tead和第二个因子的协同作用是Foxa2在该节点表达的核心机制，并且该机制是进化保守的。由于Tead表达广泛，第二因子的表达应局限于原始条纹区，该因子应与Tead共同调控原始条纹区基因的表达。Tead家族由四种密切相关的蛋白质组成。为了揭示个体基因的作用，我们制作了敲除小鼠。Tead1;Tead2双突变胚缺乏Foxa2表达，且体后轴延伸缺陷，提示Tead1/2在中央区建立中起核心作用。

Posterior extension of body axis is achieved by sequential addition of more posterior tissues in the primitive streak region, which consists of the node and the primitive streak. We previously found that core element of the node/notochord enhancer of Foxa2 gene drives gene expression specifically in the primitive streak region. Thus, to address the mechanism of establishment of the primitive streak region, we analyzed the regulatory mechanism of the core element. The core element is activated in the Wnt/β-catenin treated P19 cells, and this activation depends on the binding sites for two transcription factors. These binding sites are also essential for the in vivo activity of the node/notochord enhancer. One of the enhancer binding proteins is Tead, and inhibition of Tead activity by Tead-EnR in transgenic mouse embryos resulted in the loss of the notochord. Modulation of Tead activity in zebrafish embryos also altered foxa2 expression in the embryonic shield. These findings suggest that cooperation of Tead and a second factor is the central mechanism of Foxa2 expression in the node, and that this mechanism is evolutionally conserved. Since Tead is expressed widely, expression of the second factor should be restricted to the primitive streak region and this factor and Tead should cooperatively regulate gene expression in the primitive streak region. Tead family consists of four closely related proteins. To reveal the role of individual genes, we made knock out mice. Tead1 ; Tead2 double mutant embryos lack Foxa2 expression, and has defects in posterior body axis extension, suggesting that Tead1/2 play central roles in establishment of the central region.