A transgene-free, human peri-gastrulation embryo model with trilaminar embryonic disc-, amnion- and yolk sac-like structures

The ultimate outcome of the gastrulation in mammalian development is a recognizable trilaminar disc structure containing organized cell lineages with spatially defined identities in an emerging coordinate system ^1–4 . Despite its importance in human development, gastrulation remains difficult to study. Stem cell-based embryo models, including those that recapitulate different aspects of pre- and peri-gastrulation human development ^5–15 , are emerging as promising tools for studying human embryogenesis ^16–18 . However, it remains unclear whether existing human embryo models are capable of modeling the development of the trilaminar embryonic disc structure, a hallmark of human gastrulation. Here we report a transgene-free human embryo model derived solely from primed human pluripotent stem cells (hPSCs), which recapitulates various aspects of peri-gastrulation human development, including formation of trilaminar embryonic layers situated between dorsal amnion and ventral definitive yolk sac and primary hematopoiesis. We term this model the peri-gastrulation trilaminar embryonic disc (PTED) embryoid. The development of PTED embryoid does not follow natural developmental sequences of cell lineage diversification or spatial organization. Instead, it exploits both extrinsic control of tissue boundaries and intrinsic self-organizing properties and embryonic plasticity of the diverse peri-gastrulation-stage cell lineages, leading to the emergence of in vivo -like tissue organization and function at a global scale. Our lineage tracing study reveals that in PTED embryoids, embryonic and extraembryonic mesoderm cells, as well as embryonic and extraembryonic endoderm cells, share common progenitors emerging during peri-gastrulation development. Active hematopoiesis and blood cell generation are evident in the yolk sac-like structure of PTED embryoids. Together, PTED embryoids provide a promising and ethically less challenging model for studying self-organizing properties of peri-gastrulation human development.