Tracing and Capturing the Epiblast Pluripotency of Sheep Preimplantation Embryos

Capturing different pluripotent state stem cells from epiblast in vitro helps understand embryonic development and provides invaluable cell sources for basic research and regenerative medicine. Sheep are not only one of the most important livestock species in agriculture but also serve as an ideal preclinical model for studying human disease. Single-cell transcriptome analysis of sheep preimplantation embryos from embryonic day (E) 1 to E14 is performed to investigate the pluripotency changes of epiblast and elucidate the pluripotent regulation signaling. By combination of growth factors or inhibitors of JAK/STAT3, FGF, WNT, and TGF-β pathways in the culture medium, sheep formative and primed pluripotent stem cells (sfPSCs and spPSCs) are established respectively. The newly derived PSCs could maintain over 100 passages and differentiate into three germ layers. In addition, sfPSCs and spPSCs exhibit different molecular features, and sfPSCs have the ability of contribution to ICM and can be used as donor cells for producing cloned embryos efficiently. A cross-species comparison of early embryo development in mouse, pig and sheep illustrates the conservation of the epiblast naïve to primed state transition process and the divergence of the developmental events time points, the specific gene expression patterns and pluripotent regulation signaling. These studies are expected to improve our understanding of mammal early embryo development and present a reference for defining pluripotency.