Reduced MEK inhibition preserves genomic stability in naïve human ES cells

Human embryonic stem cells (hESCs) can be captured in a primed state resembling the postimplantation epiblast or in a naïve state resembling the preimplantation epiblast. Naïve conditions allow the study of preimplantation development ex vivo but reportedly lead to chromosomal abnormalities, compromising their utility in research and potential therapeutic applications. Although MEK inhibition is essential for the naïve state, here we show that reduced MEK inhibition facilitates the establishment and maintenance of naïve hESCs that retain naïve-specific features, including global DNA hypomethylation, HERVK expression and X chromosome reactivation. We further show that hESCs cultured under these modified conditions proliferate more rapidly, accrue fewer chromosomal abnormalities and display changes in the phosphorylation levels of MAPK components, regulators of DNA damage/repair, and cell cycle. We thus provide a simple modification to current methods to enable robust growth and reduced genomic instability in naïve hESCs.