After dissection, cells were cross-linked by 5 min of 1% formaldehyde treatment at 37˚C. The chromatin was sonicated using Bioruptor UCD-250. After IP, stringent washes, reverse cross-linked and proteinase K treatment, DNA was extracted using PCR purification kit (QIAGEN). ChIP-seq library were prepared with ChIP-seq sample prep kit (illumina) for the paired end read Illumina HiSeq 2000 platform.