Studies on the establishment of the primitive streak region

体轴的后伸是通过在原始条纹区域顺序增加更多的后方组织来实现的，原始条纹区域由结点和原始条纹组成。我们先前发现，Foxa2基因的结节/脊索增强子的核心元件驱动基因在原始条纹区域特异性地表达。因此，为了解决原始条纹区域的建立机制，我们分析了核心元件的调节机制。在Wnt/β-catenin处理的P19细胞中，核心元件被激活，这种激活依赖于两个转录因子的结合位点。这些结合位点对结节/脊索增强子的体内活性也是必不可少的。增强子结合蛋白之一是TEAD，在转基因小鼠胚胎中，TEAD-ENR抑制TEAD活性会导致脊索的丧失。斑马鱼胚胎中TEAD活性的调节也改变了胚盾中FOXA2的表达。这些发现表明，TEAD和第二因子的协同作用是Foxa2在结节表达的中心机制，并且这种机制在进化上是保守的。由于TEAD广泛表达，第二因子的表达应限制在原始条纹区域，该因子与TEAD应协同调节原始条纹区域的基因表达。TEAD家族由四个密切相关的蛋白质组成。为了揭示单个基因的作用，我们让基因敲除小鼠。Tead1；Tead2双突变胚胎缺乏Foxa2的表达，且后体轴伸展存在缺陷，提示Tead1/2在中心区的建立中起核心作用。

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.