design: ChIP-seq was performed following the protocol described by Johnson et al. (2007) {Johnson, 2007 #1612} with minor modifications. Cells were cross-linked with 1% formaldehyde at room temperature for 10 minutes to preserve protein-DNA interactions, and the reaction was quenched by the addition of 125 mM glycine. Nuclei were isolated and lysed to release chromatin, which was subsequently sheared to an average fragment size of 200500 bp using a Bioruptor sonicator (Diagenode). Immunoprecipitation was performed overnight at 4C with Anti-CTCF Antibodie (Millipore, Cat. No. 07-729-25UL) and Rabbit Control IgG (Abclonal, Cat. No.AC005). Protein-DNA complexes were captured using magnetic protein A/G beads (Thermo, Cat. No. 88802), followed by reverse cross-linking with proteinase K (QIAGEN, Cat. No. 19133) at 65C for 6 hours. DNA was extracted using a PCR purification kit (Qiagen) according to the manufacturers instructions. Sequencing libraries were prepared using the MGIEasy Universal DNA Library Prep Kit (MGI, Cat. No. 1000006985) and sequenced on an MGISEQ-2000 platform to generate paired-end 100 bp reads.