Single-Cell Analysis of Embryoids Reveals Lineage Diversification Roadmaps of Early Human Development

Despite its clinical and basic importance, our understanding of early human development remains limited. Stem cell-derived, embryo-like structures (or embryoids) allowing studies of embryonic development without using natural embryos can potentially help fill the knowledge gap of human development. Herein, transcriptome at the single-cell level of a human embryoid model, which recapitulates aspects of lineage diversification and three-dimensional tissue architecture of the human embryo from the implantation to the onset of gastrulation, was profiled at different time points. Molecular maps of lineage diversifications from the pluripotent human epiblast towards the amniotic ectoderm, primitive streak / mesoderm, and primordial germ cells were constructed and compared with in vivo primate data. Similarly, chimpanzee embryoids were generated and profiled to reveal transcriptome dynamics during the early post-implantation chimpanzee development. Our comparative transcriptome analyses reveal a critical role of NODAL signaling in human mesoderm and primordial germ cell specification, which is further functionally validated. Through comparative transcriptome analyses and validations with human blastocysts and in vitro cultured cynomolgus embryos, we further proposed stringent criteria for distinguishing between human trophectoderm and amniotic ectoderm cells. Altogether, this study provides new knowledge of the lineage diversification roadmap of early human development and will serve as a valuable resource for studying human development.