Strange IndiaStrange India

Recently, several studies using cultures of human embryos together with single-cell RNA-seq (scRNA-seq) analyses have revealed differences between humans and mice, necessitating the study of human embryos 1-8. Despite the importance of human embryology, ethical and legal restrictions have limited post-implantation stage studies. Thus, recent efforts have focused on developing in vitro self-organising models using human stem cells 9-17. Here, we report genetic and non-genetic approaches to generate authentic hypoblast cells (nHyC)—known to give rise to one of the two extraembryonic tissues essential for embryonic development—from naïve human pluripotent stem cells (hPSCs). Our nHyCs spontaneously assemble with naïve hPSCs to form a three-dimensional bilaminar structure (bilaminoids) with a pro-amniotic-like cavity. In the presence of additional naïve hPSC-derived analogues of the second extraembryonic tissue, the trophectoderm, the efficiency of bilaminoid formation increases from 20% to 40%, and the epiblast within the bilaminoids continues to develop in response to trophectoderm-secreted IL6. Furthermore, we show that bilaminoids robustly recapitulate the patterning of the anterior-posterior axis and the formation of cells reflecting the pre-gastrula stage, whose emergence can be shaped by genetically manipulating the DKK1/OTX2 hypoblast-like domain. We have thus successfully modelled and revealed the mechanisms by which the two extraembryonic tissues efficiently guide the stage-specific growth and progression of the epiblast as it establishes the post-implantation landmarks of human embryogenesis.

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