Epigenetic reversion of post-implantation epiblast to pluripotent embryonic stem cells

Abstract

The pluripotent state, first established in the primitive ectoderm cells of the blastocyst-stage embryo, is lost during subsequent development. Bao et al. now show that advanced post-implantation epiblast cells from mouse embryos aged up to 7.5 days can be reprogrammed back to pluripotency by exposure to LIF/STAT3 signalling. They show accompanying changes in the transcriptome (the total mRNA in the cell) results in a loss of the phenotypic and epigenetic memory found in epiblast cells. Cells reprogrammed in this way can contribute to somatic tissues and germ cells in chimaeras, unlike self-renewing epiblast stem cells. This work provides a model for studying how signalling and epigenetic reprogramming may promote reacquisition of pluripotency. The pluripotent state is first established in the primitive ectoderm cells of blastocysts but is progressively and irreversibly lost during development. For example, the transition from primitive ectoderm cell to epiblast cell, post implantation, involves significant transcriptional and epigenetic changes. A technique for reprogramming advanced epiblast cells from embryonic day 5.5–7.5 mouse embryos to embryonic-stem-cell-like cells — representing a return to pluripotency — is now demonstrated. The pluripotent state, which is first established in the primitive ectoderm cells of blastocysts, is lost progressively and irreversibly during subsequent development1. For example, development of post-implantation epiblast cells from primitive ectoderm involves significant transcriptional and epigenetic changes, including DNA methylation and X chromosome inactivation2, which create a robust epigenetic barrier and prevent their reversion to a primitive-ectoderm-like state. Epiblast cells are refractory to leukaemia inhibitory factor (LIF)–STAT3 signalling, but they respond to activin/basic fibroblast growth factor to form self-renewing epiblast stem cells (EpiSCs), which exhibit essential properties of epiblast cells3,4 and that differ from embryonic stem (ES) cells derived from primitive ectoderm5. Here we show reprogramming of advanced epiblast cells from embryonic day 5.5–7.5 mouse embryos with uniform expression of N-cadherin and inactive X chromosome to ES-cell-like cells (rESCs) in response to LIF–STAT3 signalling. Cultured epiblast cells overcome the epigenetic barrier progressively as they proceed with the erasure of key properties of epiblast cells, resulting in DNA demethylation, X reactivation and expression of E-cadherin. The accompanying changes in the transcriptome result in a loss of phenotypic and epigenetic memory of epiblast cells. Using this approach, we report reversion of established EpiSCs to rESCs. Moreover, unlike epiblast and EpiSCs, rESCs contribute to somatic tissues and germ cells in chimaeras. Further studies may reveal how signalling-induced epigenetic reprogramming may promote reacquisition of pluripotency.