Abstract
Pluripotent stem cells (PSCs) have been derived from various species, but most culture systems stabilize only a single PSC type. By contrast, epiblast cells in vivo exist along a continuum and interact dynamically with both embryonic and extraembryonic cells, interactions missing in standard PSC cultures. This absence limits the self-organizing potential of PSCs and leads to disorganized tissue formation in teratomas. To address this, we developed a unified culture system that supports the stable differentiation of epiblast-like cells into multiple key human gastrulating cell types, collectively called human gastrulating stem cells (hGaSCs). hGaSCs, composed of endoderm-like, mesoderm-like, ectoderm-like, amnion ectoderm-like, and primordial germ cell-like cells, maintain a stable balance during long-term culture. In 3D culture, hGaSCs self-assemble into gastruloid-like structures (hGaSC-gastruloids) that model aspects of a Carnegie Stage 7 human embryo, including gastrulation and germ layer specification. Using hGaSC-gastruloids, we modeled the effects of valproic acid (VPA) on human gastrulation and uncovered molecular pathways underlying VPA-induced malformations. When transplanted into the seminiferous tubules, hGaSCs formed embryo-like structures, progressing through fetal tissue and organ development, unlike the disorganized growth seen in teratomas. In conclusion, hGaSCs provide a versatile platform to study human gastrulation, early organogenesis, developmental defects, and drug teratogenicity, with promising applications in tissue and organ generation from cultured stem cells.