Efficient stem cell-derived mouse embryo models for environmental studies

Blastoids are stem cell-derived structures that mimic natural blastocysts by incorporating all three lineages: trophectoderm, epiblast, and primitive endoderm. However, current methods often yield incomplete structures that fail to cavitate or to form a proper primitive endoderm. To overcome these limitations, we develop a modular approach by aggregating three murine stem cell types: embryonic stem cells (ESCs), ESCs with inducible GATA4 expression (iG4-ESCs), and trophoblast stem cells (TSCs). This method yields cavitated blastocyst-like structures—termed iG4-blastoids—with approximately 80% efficiency. Single-cell RNA sequencing confirms their close resemblance to mature mouse blastocysts. Notably, culturing iG4-blastoids without FGF4 enhances specification of the invasive mural trophectoderm, and approximately 12% of structures undergo post-implantation-like morphogenesis in vitro. Using this model, we show that caffeine, alcohol, nicotine, and amino acid variations affect iG4-blastoids and natural embryos similarly, underscoring their utility as a robust model for investigating the impact of diverse environmental factors on embryogenesis.