Indirect evidence suggests that blastopore closure during gastrulation of anamniotes, including amphibians such as Xenopus laevis, depends on circumblastoporal convergence forces generated by the marginal zone (MZ), but direct evidence is lacking. We show that explanted MZs generate tensile convergence forces up to 1.5 μN during gastrulation and over 4 μN thereafter. These forces are generated by convergent thickening (CT) until the midgastrula and increasingly by convergent extension (CE) thereafter. Explants from ventralized embryos, which lack tissues expressing CE but close their blastopores, produce up to 2 μN of tensile force, showing that CT alone generates forces sufficient to close the blastopore. Uniaxial tensile stress relaxation assays show stiffening of mesodermal and ectodermal tissues around the onset of neurulation, potentially enhancing long-range transmission of convergence forces. These results illuminate the mechanobiology of early vertebrate morphogenic mechanisms, aid interpretation of phenotypes, and give insight into the evolution of blastopore closure mechanisms.

中文翻译：

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在非洲爪蟾胚孔闭合和体轴伸长过程中，大范围的长距离拉力驱动收敛


间接证据表明，羊膜动物（包括非洲爪蟾等两栖动物）原肠胚形成期间胚孔的关闭取决于边缘区（MZ）产生的周胚孔会聚力，但缺乏直接证据。我们发现，外植的 MZ 在原肠胚形成期间产生高达 1.5 μN 的拉伸收敛力，此后产生超过 4 μN。这些力是通过直至中原肠胚的会聚增厚 (CT) 产生的，此后逐渐通过会聚延伸 (CE) 产生。来自腹侧胚胎的外植体缺乏表达 CE 的组织，但关闭其胚孔，产生高达 2 μN 的拉力，表明 CT 单独产生足以关闭胚孔的力。单轴拉伸应力松弛试验显示神经形成开始周围的中胚层和外胚层组织变硬，可能增强会聚力的长距离传递。这些结果阐明了早期脊椎动物形态发生机制的力学生物学，有助于解释表型，并深入了解胚孔关闭机制的进化。