Abstract
Recapitulating mammalian embryonic development in vitro is a major challenge in biology. It has been shown that gastruloids1–5 and ETX embryos6 can display hallmarks of gastrulation in vitro. However, these models fail to progress beyond spatially segregated, yet amorphous cellular assemblies. Systems such as organoids7 do show tissue stratification and organogenesis, but require adult stem cells or exogeneous induction of specific cell fates, and hence do not reflect the emergent organization of embryonic development. Notably, gastruloids are derived exclusively from embryonic stem cells (ESCs), whereas, in vivo, crucial patterning cues are provided by extraembryonic cells8. Here, we show that assemblies of mouse ESCs (mESCs) and extraembryonic endoderm (XEN) cells can develop beyond gastrulation and produce a central hallmark of organogenesis: stratified neural epithelia resembling a neural tube, which can be further differentiated to cerebral cortex-like tissue. By single-cell RNA-seq, we show that our model has a larger cell type diversity than existing models, and that mESCs and XEN cells impact each other’s differentiation. XEN cells promote neural tube formation through local inhibition of primitive streak formation. In turn, the presence of mESCs drives XEN cells to resemble visceral endoderm, which envelops the embryo in vivo. This study provides a model system to investigate neurulation and extraembryonic endoderm development, and may serve as a starting point to generate embryo models that advance further toward the formation of the vasculature, nervous system, and digestive tube.
