During reprogramming with mES medium, Bmi1, Ctcf, Ezh2, Kdm2b, and Wdr5 were overexpressed simultaneously with the four Yamanaka factors (OKMS+5F) or Oct4 (O+5F). All factors were delivered simultaneously via a retrovirus system on day 0 and 1. Reprogramming with only Yamanaka factors (OKMS) or Oct4 (O) served as control. The histone methylation on core pluripotency loci was determined on day 6 with ChIP-qPCR (G). 