Single-cell RNA-seq reveals sequential trophoblast transition during human embryo implantation

We performed single-cell RNA sequencing (scRNA-seq) analysis of human post-implantation trophoblast cells. A hierarchical model was established, which was characterized by the sequential and stepwise development of two primitive cytotrophoblast cell (pCTB) subtypes after the trophectoderm (TE), two primitive syncytiotrophoblast (pSTB) subtypes, and migrative trophoblast cells (MTB). Further analysis characterized a new subtype of fusion-competent cells, which not only prepare for fusion to form primitive syncytiotrophoblast but also possess migration ability, which could be dual-function cells during implantation. Our work allows for reconstruction of sequential trophoblast cell transcriptional programs transition during implantation and provides a valuable resource to study pathologies in early pregnancy, such as recurrent implantation failure. Overall design: Combining the in vitro culture of human embryos to the post-implantation stage with scRNA-seq technology, we developed a comprehensive resource characterizing the transcriptional dynamics of trophoblast specification. RNA was extracted from 12 human embryos from day 8 to day 13.