About 5 x 10^5 to 5 x 10^6 cells were crosslinked using formaldehyde (a final 1% (v/v); Sigma, F8775-500ML), followed by quenching with a Glycine (final 125 mM; Sigma, G8898-1KG), mixed well and incubated for another 10 min. Cells were pelleted and washed once with ice-cold 1x PBS. After removing the supernatant, the cell pellets were stored at -80°C or directly used for the following Hi-C experiments. For ATAC-seq, First, 5 × 10^4 cells were spun at 500 g for 5 min, 4 °C, which was followed by a wash using 50 μl of cold 1× PBS and centrifugation at 500 g for 5 min, 4 °C. Cells were resuspended in 50 μl cold lysis buffer (10 mM Tris-HCl, pH 7.4, 10 mM NaCl, 3 mM MgCl2 and 0.1% (v/v) Igepal CA-630) and centrifugation at 500 g for 10 min, 4 °C. Second, the pellet was resuspended in the transposase reaction mix (25 μl 2× TD buffer, 2.5 μl transposase (Illumina, FC-121-1030) and 22.5 μl nuclease-free water). The transposition reaction was carried out for 30 min at 37 °C. Then, the samples were purified by using a Qiagen MinElute PCR Purification Kit (Qiagen, 28004) and amplified by PCR. After size selected by VAHTS DNA Clean Beads, the samples were sequenced by HiSeq X Ten at Novogene. ChIP-seq sequencing libraries were generated by Tn5 transposase and then PCR amplification and size selected by VAHTS DNA Clean Beads. Libraries were sent for high throughput sequencing with the HiSeq X Ten at Novogene.