E14TG2a ESCs derived from 129/Ola were cultured in GMEM supplemented non-essential amino acids, 10% Knockout Serum Replacement, sodium pyruvate, L-glutamine, 2-mercaptoethanol, penicillin, streptomycin, and leukemia inhibitory factor without feeder cells. ChIP experiment with anti-H3K4me3 antibody was performed as we have described previously. Samples destined for ChIP seq by Illumina HiSeq were prepared according to the manufacturer’s instructions.