Post-gastrulation amnioids as a stem cell-derived model of human extra-embryonic development

The amnion, an extra-embryonic tissue in mammalian embryos, is thought to provide crucial signaling, structural, and nutritional support during pregnancy. Despite its pivotal importance, studying human amnion formation and function has been hampered by the lack of accurate in vitro models. Here, we present an embryonic stem cell-derived 3D model of the post-gastrulation amnion, post-gastrulation amnioids (PGAs), that faithfully recapitulates extra-embryonic development up to 4 weeks post-fertilization, closely mimicking the functional traits of the human amniotic sac. PGAs self-organize, forming the amnion and the yolk sac, and are surrounded by the extra-embryonic mesoderm. Using PGAs, we show that GATA3 is required and sufficient for amniogenesis and that an autoregulatory feedback loop governs amnion formation, whereby extra-embryonic signals promote amnion specification. The reproducibility and scalability of the PGA system, with its precise cellular, structural, and functional integrity, opens avenues for investigating embryo-amnion interactions beyond gastrulation and offers an ideal platform for large-scale pharmacological and clinical studies.