Cells were crosslinked by 1% paraformaldehyde for 10 minutes at room temperature and then quenched by 0.125M glycine for 5 minutes. Cells were lysed on ice for 30 minutes with lysis buffer containing 10 mM Tris-HCl (pH 8.0), 1 mM EDTA (pH 8.0), 140 mM NaCl, 1% Triton X-100, 0.2% SDS, 0.1% deoxycholic acid. Chromatin DNA was fragmented to around 200-500bp by Diagenode BioruptorPico sonicator for 45 cycles of 30 seconds on and 30 second off, and then incubated overnight with anti-H3K4me3 or H3K27ac or H3K9ac antibody and Dynabead (Life Technologies) at 4C. Next day, immune complexes were washed once with RIPA buffer with 500mM NaCl and once with LiCl wash buffer (10 mM Tris-HCl (pH 8.0), 1 mM EDTA (pH 8.0), 250 mM LiCl, 0.5% NP-40, 0.5% deoxycholic acid). DNA was then reverse crosslinked and eluted overnight in elution buffer (10 mM Tris-Cl (pH 8.0), 5 mM EDTA, 300 mM NaCl, 0.5% SDS, 20 mg/ml proteinase K) at 65C. The third day, eluted DNA was purified by AMPure beads (Beckman-Coulter). NEB Next Ultra DNA Library kit was used to prepare library