Complete human day 14 post-implantation embryo models from naïve ES cells

The ability to study human post-implantation development remains limited due to ethical and technical challenges associated with intrauterine development after implantation1. Embryo-like models with spatially organized morphogenesis of all defining embryonic and extra-embryonic tissues of the post-implantation human conceptus (i.e., embryonic disk, bilaminar disk, yolk- and chorionic sacs, surrounding trophoblasts) remain lacking2. Mouse naïve embryonic stem cells (ESCs) have recently been shown to give rise to embryonic and extra-embryonic stem cells capable of self-assembling into post-gastrulation mouse Structured Stem cell-based Embryo Models with spatially organized morphogenesis (SEMs)3. Here, we extend these findings to humans, while using only genetically unmodified human naïve ESCs (in HENSM conditions)4. Such human fully integrated SEMs recapitulate the organization of nearly all known lineages and compartments of post-implantation human embryos including epiblast, hypoblast, extra-embryonic mesoderm, and trophoblast surrounding the latter layers. These human complete SEMs demonstrated developmental growth dynamics that resemble key hallmarks of post-implantation stage embryogenesis up to 13-14 days post-fertilization (dpf) (Carnegie stage 6a). This includes embryonic disk and bilaminar disk formation, epiblast lumenogenesis, polarized amniogenesis, anterior-posterior symmetry breaking, PGC specification, polarized yolk sac with visceral and parietal endoderm, extra-embryonic mesoderm expansion that defines a chorionic cavity and a connecting stalk, a trophoblast surrounding compartment demonstrating syncytium and lacunae formation. This SEM platform may enable the experimental interrogation of previously inaccessible windows of human early post-implantation up to peri-gastrulation development.