Deciphering the epigenetic context of pluripotency in rabbit pre-implantation embryos
Résumé
Pluripotency describes the ability of a stem cell to give rise to all cell types in mature organisms. Two main types of pluripotent stem cells (PSCs) have been described: naïve and primed. In rodents, naïve-state pluripotency characterises mouse embryonic stem cells (mESCs) that have been derived from the pre-implantation epiblast. In primates (human and monkey) and lagomorphs (rabbits), ESCs only exist in the primed state of pluripotency. Primed-state pluripotency characterises the epiblast of developmentally more advanced embryos, with a higher concentration of heterochromatin and an inactivated X chromosome in female cells. The study aimed to decipher the chromatin context of naïve and primed pluripotency in the rabbit embryo, from the compacted morula stage until the onset of the gastrulation in the epiblast. Using immuno-fluorescence, we analysed the distribution of DNA-methylation and hydroxymethylation, Histone 3 lysine 9 and 27 methylation, as well as Histone 2A lysine 119 ubiquitination. In parallel, we analysed the expression of genes encoding the erasers and writers of those epigenetic marks using single-cell Biomark qPCR. From these experiments, we observed a progressive loss of heterochromatin marks in the pluripotent cells of early blastocysts (Inner Cell Mass or ICM), followed by gain of heterochromatin in more advanced stages (in the epiblast). Those variations are associated with the transient downregulation of genes promoting heterochromatin formation in the ICM, while genes promoting euchromatin formation are downregulated in the epiblast. This study helped us to identify the chromatin landscape and its regulators associated to the naïve state of pluripotency in rabbits.