Shaping the early amniote embryo Gastrulation is an essential step in development in which the internal tissues of the body are set apart. In birds and mammals, a similar cascade of molecular events is known to specify embryonic territories, but how they are physically remodeled has remained elusive. Working with avian embryos, Saadaoui et al. identified a cable that encircles the embryo as the engine of gastrulation and described the collective cell movements as similar to the motion of a fluid. One side of this contractile ring pulls more strongly than the other, entraining the large-scale tissue movements that shape the early body plan. The embryo margin, previously known to function in molecular regulation, thus emerges as a dual mechanical and molecular organizer of development. Science, this issue p. 453 During chick embryo gastrulation, a supracellular actomyosin ring remodels the embryonic territory and shapes the primitive streak. Tissue morphogenesis is driven by local cellular deformations that are powered by contractile actomyosin networks. How localized forces are transmitted across tissues to shape them at a mesoscopic scale is still unclear. Analyzing gastrulation in entire avian embryos, we show that it is driven by the graded contraction of a large-scale supracellular actomyosin ring at the margin between the embryonic and extraembryonic territories. The propagation of these forces is enabled by a fluid-like response of the epithelial embryonic disk, which depends on cell division. A simple model of fluid motion entrained by a tensile ring quantitatively captures the vortex-like “polonaise” movements that accompany the formation of the primitive streak. The geometry of the early embryo thus arises from the transmission of active forces generated along its boundary.

中文翻译：

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张力环驱动组织流动以塑造形成原肠的羊膜胚胎

塑造早期羊膜胚胎原肠胚形成是发育过程中必不可少的一步，在这个过程中，身体的内部组织是分开的。在鸟类和哺乳动物中，已知一连串类似的分子事件可以指定胚胎领域，但它们的物理重塑方式仍然难以捉摸。Saadaoui 等人研究了禽类胚胎。确定了一条环绕胚胎的电缆作为原肠胚形成的引擎，并将集体细胞运动描述为类似于流体的运动。这个收缩环的一侧比另一侧拉力更大，带动形成早期身体计划的大规模组织运动。胚胎边缘，以前已知在分子调节中起作用，因此作为发育的双重机械和分子组织者出现。科学，这个问题 p。453 在鸡胚原肠胚形成期间，细胞上肌动球蛋白环重塑胚胎区域并塑造原始条纹。组织形态发生是由由收缩性肌动球蛋白网络驱动的局部细胞变形驱动的。局部力如何跨组织传递以在细观尺度上塑造它们仍不清楚。分析整个鸟类胚胎的原肠胚形成，我们表明它是由胚胎和胚胎外区域之间边缘的大规模细胞上肌动球蛋白环的分级收缩驱动的。这些力的传播是通过上皮胚胎盘的流体样反应实现的，这取决于细胞分裂。一个简单的由拉伸环携带的流体运动模型定量地捕捉了伴随原始条纹形成的涡旋状“极化”运动。