Yanagi Takanori, Ito Kenta, Nishihara Akiha, Minamino Reika, Mori Shoko, Sumida Masayuki, Hashimoto Chikara
JT Biohistory Research Hall, 1-1 Murasaki-cho, Takatsuki, Osaka, 569-1125, Japan; Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka, 560-0043, Japan.
Dev Growth Differ. 2015 Apr;57(3):218-31. doi: 10.1111/dgd.12200. Epub 2015 Mar 10.
The dorsal blastopore lip (known as the Spemann organizer) is important for making the body plan in amphibian gastrulation. The organizer is believed to involute inward and migrate animally to make physical contact with the prospective head neuroectoderm at the blastocoel roof of mid- to late-gastrula. However, we found that this physical contact was already established at the equatorial region of very early gastrula in a wide variety of amphibian species. Here we propose a unified model of amphibian gastrulation movement. In the model, the organizer is present at the blastocoel roof of blastulae, moves vegetally to locate at the region that lies from the blastocoel floor to the dorsal lip at the onset of gastrulation. The organizer located at the blastocoel floor contributes to the anterior axial mesoderm including the prechordal plate, and the organizer at the dorsal lip ends up as the posterior axial mesoderm. During the early step of gastrulation, the anterior organizer moves to establish the physical contact with the prospective neuroectoderm through the "subduction and zippering" movements. Subduction makes a trench between the anterior organizer and the prospective neuroectoderm, and the tissues face each other via the trench. Zippering movement, with forming Brachet's cleft, gradually closes the gap to establish the contact between them. The contact is completed at the equator of early gastrulae and it continues throughout the gastrulation. After the contact is established, the dorsal axis is formed posteriorly, but not anteriorly. The model also implies the possibility of constructing a common model of gastrulation among chordate species.
背侧胚孔唇（即斯佩曼组织者）在两栖类原肠胚形成过程中对构建身体蓝图起着重要作用。人们认为组织者会向内卷入并向动物极迁移，以便在中晚期原肠胚的囊胚腔顶部与预期的头部神经外胚层进行物理接触。然而，我们发现这种物理接触在多种两栖类物种的极早期原肠胚的赤道区域就已经建立。在此，我们提出了一个两栖类原肠胚运动的统一模型。在该模型中，组织者存在于囊胚的囊胚腔顶部，向植物极移动并定位在原肠胚形成开始时从囊胚腔底部到背唇的区域。位于囊胚腔底部的组织者形成包括前索板在内的前轴中胚层，而位于背唇的组织者最终形成后轴中胚层。在原肠胚形成的早期阶段，前组织者通过“内陷和拉链式”运动移动以与预期的神经外胚层建立物理接触。内陷在前组织者和预期的神经外胚层之间形成一条沟，组织通过这条沟相互面对。拉链式运动伴随着形成布拉凯特氏裂，逐渐缩小间隙以在它们之间建立接触。这种接触在早期原肠胚的赤道处完成，并在整个原肠胚形成过程中持续。接触建立后，背轴在后部形成，而非前部。该模型还暗示了构建脊索动物物种间原肠胚形成通用模型的可能性。
