p53 is essential for DNA methylation homeostasis in naïve embryonic stem cells, and its loss promotes clonal heterogeneity.

DNA methylation is a key regulator of embryonic stem cell (ESC) biology, dynamically changing between naïve, primed, and differentiated states. The p53 tumor suppressor is a pivotal guardian of genomic stability, but its contributions to epigenetic regulation and stem cell biology are less explored. We report that, in naïve mouse ESCs (mESCs), p53 restricts the expression of the de novo DNA methyltransferases Dnmt3a and Dnmt3b while up-regulating Tet1 and Tet2, which promote DNA demethylation. The DNA methylation imbalance in p53-deficient (p53-/-) mESCs is the result of augmented overall DNA methylation as well as increased methylation landscape heterogeneity. In differentiating p53-/- mESCs, elevated methylation persists, albeit more mildly. Importantly, concomitant with DNA methylation heterogeneity, p53-/- mESCs display increased cellular heterogeneity both in the "naïve" state and upon induced differentiation. This impact of p53 loss on 5-methylcytosine (5mC) heterogeneity was also evident in human ESCs and mouse embryos in vivo. Hence, p53 helps maintain DNA methylation homeostasis and clonal homogeneity, a function that may contribute to its tumor suppressor activity.