A total of 50,000 cells were washed once with cold PBS and resuspended in 50ul lysis buffer. The suspension of nuclei was then centrifuged for 10 min at 500g at 4°C, followed by the addition of 50 μl transposition reaction mix (25 μl TD buffer, 2.5 μl Tn5 transposase and 22.5 μl nuclease-free H2O) of Nextera DNA library Preparation Kit (96 samples) (FC-121-1031, Illumina), and incubated at 37°C for 30min. DNA was isolated using a MinElute Kit (Qiagen). ATAC-seq libraries were first subjected to 5 cycles of pre-amplification. To determine the suitable number of cycles required for the second round of PCR the library was assessed by quantitative PCR as described5, and the library was then PCR amplified for the appropriate number of cycles. Libraries were purified with a Qiaquick PCR (Qiagen) column. Library concentration was measured using a KAPA Library Quantification kits (KK4824) according to the manufacturers instructions. Library integrity was checked by gel electrophoresis. Finally, the ATAC library was sequenced on a NextSeq 500 using a NextSeq 500 High Output Kit v2 (150 cycles) (FC-404-2002, Illumina) according to the manufacturers instructions.