Impairment of DNA methylation maintenance is the main cause of global demethylation in naive embryonic stem cells by von Meyenn, F, Iurlaro, M, Habibi, E, Liu, N, Salehzadeh-Yazdi, A, Santos, F, Petrini, E, Milagre, I, Yu, M, Xie, Z, Kroeze, L, Nesterova, T, Jansen, J, Xie, H, He, C, Reik, W, Stunnenberg, H