A good artificial mouse embryo created by University of Cambridge researchers has all its parts in all the right places, other than that it has a cavity where its yolk sac ought to be. And so it recapitulates many of the developmental milestones that are attained by natural embryos, except that without a yolk sac, it may develop only so far. Regardless, the artificial embryo provides embryonic stem cells (ESCs) at one end plus extraembryonic trophoblast stem cells (TSCs) at the other.

Within natural embryos, ESCs eventually give rise to the body, and TSCs eventually give rise to the placenta. Although the artificial embryo provides properly positioned ESCs and TSCs, as well as the benefit of the 3D scaffold, or extracellular matrix, it is not likely to improvement much beyond the post-implantation stage. Besides lacking the pv cells that would give rise to a yolk sac, the artificial embryo is not optimized…