Post-implantation, the pluripotent epiblast in a human embryo forms a central lumen, paving the way for gastrulation. Osmotic pressure gradients are considered the drivers of lumen expansion across development, but their role in human epiblasts is unknown. Here, we study lumenogenesis in a pluripotent-stem-cell-based epiblast model using engineered hydrogels. We find that leaky junctions prevent osmotic pressure gradients in early epiblasts and, instead, forces from apical actin polymerization drive lumen expansion. Once the lumen reaches a radius of ∼12 μm, tight junctions mature, and osmotic pressure gradients develop to drive further growth. Computational modeling indicates that apical actin polymerization into a stiff network mediates initial lumen expansion and predicts a transition to pressure-driven growth in larger epiblasts to avoid buckling. Human epiblasts show transcriptional signatures consistent with these mechanisms. Thus, actin polymerization drives lumen expansion in the human epiblast and may serve as a general mechanism of early lumenogenesis.

植入后，人类胚胎中的多能外胚层形成中央管腔，为原肠胚形成铺平道路。渗透压梯度被认为是发育过程中管腔扩张的驱动因素，但它们在人类外胚层中的作用尚不清楚。在这里，我们使用工程水凝胶研究基于多能干细胞的外胚层模型中的腔发生。我们发现，渗漏的连接阻止了早期外胚层的渗透压梯度，相反，来自顶端肌动蛋白聚合的力驱动管腔扩张。一旦管腔达到~12微米的半径，紧密连接就会成熟，渗透压梯度会发展以驱动进一步的生长。计算模型表明，顶端肌动蛋白聚合成刚性网络可介导初始管腔扩张，并预测较大外胚层将过渡到压力驱动生长，以避免屈曲。人类外胚层表现出与这些机制一致的转录特征。因此，肌动蛋白聚合驱动人外胚层内腔扩张，并可能作为早期内腔发生的一般机制。