H9-hESCs and A2B5+ iOPCs were cross-linked with 1% (wt/vol) formaldehyde fixation buffer, resuspended and lysed using an EZ-ChIP kit (Upstate, Millipore). To shear the cross-linked DNA, the lysates were subjected to 30 cycles of 30 seconds of sonication followed by 30 seconds of rest on ice with a Bioruptor sonicator (Diagenode, UCD-200) and incubated with protein G agarose beads and 3 μg of an anti-OCT4 antibody overnight at 4°C. After chromatin immunoprecipitation, the rest of the experiments were performed according to the manufacturer's protocols The construction of library was performed using NEBNext®UltraTM DNA Library Prep Kit for Illumina (New England Biolabs, UK) according to the manufacturer's instructions.