Cells were dissociated by trypsin-EDTA digestion and lysed in hypotonic buffer. Nuclei were collected for library construction. ATAC-seq libraries were prepared using a Chromatin Profile Kit (N248, Novoprotein). Nuclei were subjected to tagmentation for 30 mins at 37 ℃ with Transposome Mix. DNA fragments were cleaned up and amplified with AmpliMix for 9-12 cycles. Libraries were purified for sequencing.