Implantation is a hallmark of mammalian embryogenesis during which embryos establish their contacts with the maternal endometrium, remodel, and undertake growth and differentiation. The mechanisms and sequence of events through which embryos change their shape during this transition are largely unexplored. Here, we show that the first extraembryonic lineage, the polar trophectoderm, is the key regulator for remodeling the embryonic epiblast. Loss of its function after immuno-surgery or inhibitor treatments prevents the epiblast shape transitions. In the mouse, the polar trophectoderm exerts physical force upon the epiblast, causing it to transform from an oval into a cup shape. In human embryos, the polar trophectoderm behaves in the opposite manner, exerting a stretching force. By mimicking this stretching behavior in mouse embryogenesis, we could direct the epiblast to adopt the disc-like shape characteristic of human embryos at this stage. Thus, the polar trophectoderm acts as a conserved regulator of epiblast shape.

植入是哺乳动物胚胎发生的标志，在此期间胚胎与母体子宫内膜建立接触、重塑并进行生长和分化。在此过渡期间胚胎改变其形状的机制和事件顺序在很大程度上尚未探索。在这里，我们展示了第一个胚胎外谱系，极地滋养外胚层，是重塑胚胎外胚层的关键调节因子。免疫手术或抑制剂治疗后其功能丧失会阻止外胚层形状转变。在小鼠中，极地滋养外胚层对外胚层施加物理力，使其从椭圆形转变为杯形。在人类胚胎中，极地滋养外胚层以相反的方式表现，施加拉伸力。通过模仿小鼠胚胎发生中的这种拉伸行为，在这个阶段，我们可以指导外胚层采用人类胚胎的盘状形状特征。因此，极性滋养外胚层作为外胚层形状的保守调节剂。