The early epiblast cells are part of the early blastocyst and are present at day 5 of human embryonic development.
These cells are considered to be ground state omnipotent stem cells, with high clonogenicity, capability of forming chimeras and teratomas (in ex-vivo experimental conditions) . These cells would typically have two activated X chromosomes in female embryos. The cells will eventually develop into the whole embryo and some extraembryonic structures.
The naive ground state of the cells lasts until late blastocyst stages (up to implantation, equivalent to day 7 in humans, E4.5 in mouse). Epiblast cells from later stages are considered primed state cells, no longer ground state. Among other differences, they are no longer capable of developing chimeras (in ex-vivo experimental conditions) and cells in female embryos will have an inactivated X chromosome.
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