Remodeling the step-wise mouse placental development by using totipotent blastomere-like stem cells [WGBS]

During development, totipotent blastomeres initiate the first cell fate decision to generate inner cell mass and trophectoderm. The trophectoderm forms the placenta mediating fetal-maternal communications, while placental deficiencies cause infertility and pregnancy disorders in humans. However, in vitro systems remodeling the step-wise placental development, particularly encompassing the pre-implantation phase, are still unavailable. Here, using mouse totipotent blastomere-like cells (TBLCs), we successfully realize inducing and long-term maintaining trophectoderm-like stem cells (TELSCs), and further generating placental trophoblast organoids. Interestingly, an intermediate morula trophectoderm-like cells (TELCs) were transiently induced from TBLCs, and quickly converted into TELSCs assembling blastocyst trophectoderm. In 3D culturing condition, TELSCs can form rosette-like structures at peri-implantation period, to eventually generate trophoblast organoids, in which trophoblast progenitors/giant cells, spongiotrophoblasts and syncytiotrophoblasts were all identified at the single-cell level. Transcriptomic and epigenomic analyses enable tracing the step-by-step transition from TBLCs to mature trophoblast lineages. Thus, this study provides a comprehensive differentiation system to understand and investigate placental development.