Yamaguti Mami, Cho Ken W Y, Hashimoto Chikara
Department of Biology, Graduate School of Science, Osaka University, Japan.
Dev Dyn. 2005 Sep;234(1):102-13. doi: 10.1002/dvdy.20523.
Spemann's organizer is a region of the gastrula stage embryo that contains future anterior endodermal and dorsal mesodermal tissues. During gastrulation, the dorsal mesoderm is divided into the prechordal mesoderm and the chordamesoderm. However, little is known regarding how this division is established. We analyzed the role of the anterior prechordal mesoderm-specific gene Xhairy2b in the regionalization of the organizer. We found that mesoderm-inducing transforming growth factor-beta signaling induced Xhairy2b expression. On the other hand, the ectopic expression of Xhairy2b induced the expression of organizer-specific genes and resulted in the formation of a secondary dorsal axis lacking head and notochord structures. We also showed that Xhairy2b down-regulated the expression of ventral mesodermal, anterior endodermal, and chordamesodermal genes. In Xhairy2b-depleted embryos, defects in the specification of anterior prechordal mesoderm identity were observed as the border between the prechordal mesoderm and the chordamesoderm was anteriorly shifted. These results suggest that Xhairy2b establishes the identity of the anterior prechordal mesoderm within Spemann's organizer by inhibiting the formation of neighboring tissues.
施佩曼组织者是原肠胚阶段胚胎的一个区域，包含未来的前端内胚层和背侧中胚层组织。在原肠胚形成过程中，背侧中胚层被分为前索中胚层和脊索中胚层。然而，关于这种划分是如何建立的，人们知之甚少。我们分析了前索中胚层特异性基因Xhairy2b在组织者区域化中的作用。我们发现，诱导中胚层的转化生长因子-β信号诱导了Xhairy2b的表达。另一方面，Xhairy2b的异位表达诱导了组织者特异性基因的表达，并导致形成了一个缺乏头部和脊索结构的次生背轴。我们还表明，Xhairy2b下调了腹侧中胚层、前端内胚层和脊索中胚层基因的表达。在Xhairy2b缺失的胚胎中，由于前索中胚层和脊索中胚层之间的边界向前移位，观察到前索中胚层身份特化存在缺陷。这些结果表明，Xhairy2b通过抑制相邻组织的形成，在施佩曼组织者内建立了前索中胚层的身份。
