Synthetic embryos complete gastrulation to neurulation and organogenesis.

Embryonic stem cells (ESC) can undergo many aspects of mammalian embryogenesis in vitro, but their developmental potential is substantially extended by interactions with extraembryonic stem cells, including trophoblast stem cells (TSCs), extraembryonic endoderm stem cells (XEN), and inducible-XEN cells (iXEN). Here, we assembled stem-cell derived embryos in vitro from mouse ESCs, TSCs and iXEN cells and showed that they recapitulate whole natural mouse embryo development in utero to day 8.5. Our embryo model displays head-folds with defined forebrain and midbrain regions and develops a beating heart-like structure, a trunk comprising a neural tube and somites, a tail bud containing neuromesodermal progenitors, a gut tube, and primordial germ cells. This complete embryo model develops within an extra-embryonic yolk sac that initiates blood island development. Importantly, we demonstrate that the neurulating embryo model assembled from Pax6 knockout-ESCs aggregated with wild-type TSCs and iXENs recapitulates the ventral domain expansion of the neural tube that occurs in natural, ubiquitous Pax6 knockout embryos. Thus, these complete embryoids are a powerful in vitro model for dissecting the roles of diverse lineages and genes in development. Our results demonstrate the self-organization ability of embryonic and two types of extra-embryonic stem cells to reconstitute mammalian development through and beyond gastrulation to neurulation and early organogenesis.