V6.5 (genotype 129SvJae × C57BL/6) and Nanog-Luciferase31 ES cells were co-cultured with irradiated C57BL/6 MEFs (GlobalStem; GSC-6002C) on pre-gelatinized plates as previously described47. Briefly, cells were cultured in mES media consisting of knock-out DMEM (Invitrogen; 10829018) supplemented with 10% FBS (GlobalStem; GSM-6002), 1% penicillin-streptomycin (Invitrogen; 15140-163), 1% L-glutamine (Invitrogen; 25030-164), 0.001% Beta-mercaptoethanol (Sigma; M3148-100ML) and 0.01% ESGRO (Millipore; ESG1106).
