Cells were fixed with 1% freshly prepared formaldehyde solution for 10min and then lysed with buffer containing: 50 mM Tris-HCl, pH 8; 10 mM EDTA; 1% SDS; x1 Proteinase inhibitor (Roche). Chromatin was sonicated and DNA–protein complexes were immune-purified with antibodies against CTCF (CS 2899S) DNA sample was used for library by following the manufacturer's recommendations of NEBNext® Ultra™ IIDNA Library Prep Kit (New England BioLabs, US). Index codes were added to each sample. Briefly, the genomic DNA was randomly fragmented to size of 350bp. DNA fragments were end polished, A-tailed, ligated with adapters, size selected and further PCR enriched. Then PCR products were purified (AMPure XP system), followed by size distribution by Agilent 2100 Bioanalyzer (Agilent Technologies, CA, USA), and quantification using real-time PCR. Library was then sequenced on NovaSeq 6000 S4 flow cell with PE150 strategy.