Establishment of bovine extraembryonic endoderm stem cells enables efficient blastoid formation.

Extraembryonic endoderm stem cells (XENs) resemble the primitive endoderm of blastocyst and provide valuable alternatives for understanding hypoblast development and building stem cell-based embryo models. Here, we report that a chemical cocktail (FGF4, BMP4, IL-6, XAV939, and A83-01) enables the de novo derivation and long-term culture of bovine XENs (bXENs) from blastocysts. Transcriptomic and epigenomic analyses confirm the identity of bXENs and reveal that bXENs resemble the hypoblast lineages of early bovine peri-implantation embryos. Furthermore, we show that bXENs maintain the stemness of expanded embryonic stem cells (EPSCs) and prevent them from undergoing differentiation. The chemical cocktail sustaining bXENs also facilitates the growth of epiblasts in developing pre-implantation embryos. Finally, 3D assembly of bXENs with bovine EPSCs and trophoblast stem cells enables efficient generation of blastoids that resemble blastocysts. bXENs and blastoids established here represent accessible in vitro models for understanding embryogenesis and improving reproductive efficiency in domestic livestock.