library_construction_protocol: Cells were dissociated by papain, filtered and kept on ice until FACS sorting. Sorted cells were collected into ice cold PBS 1X, and immediately pelleted by centrifugation (500 rcf, 5 minutes, 4°C).  50,000 – 70,000 cells were used for each experiment. Cells were washed once with 50μl PBS 1X and pelleted (500 rcf, 5 minutes, 4°C), and gently resuspended by pipetting in ice cold 50μl cold lysis buffer (10mM Tris HCl pH7.4, 10mM NaCl, 3mM MgCl2, 0.1% IGEPAL CA-630) to extract nuclei and pelleted (500 rcf, 10 minutes, 4°C). Nuclei were washed once with ice cold 50μl Tagmentation Buffer (10mM Tris HCl pH8, 5mM MgCl2) and pelleted (500 rcf, 10 minutes, 4°C). Then nuclei were tagmented in transposition reaction mix (2.5μl Tn5 Transposase (Illumina, FC-121-1030), 25μl 2X TD Buffer (Illumina, FC-121-1030), and 22.5μl nuclease free water) at 37°C for 30 minutes. DNA was purified with MinElute PCR Purification Kit (Qiagen, 28004) by 10μl 10mM Tris HCl pH8.  Library amplification was started with 1X KAPA HiFi HotStart Ready Mix, 1.25μl primers and 0.6X Sybr Green (Thermo Fisher) in total volume 50μl: 72°C for 5min; 98°C for 1min; 5 cycles of 98°C for 15sec, 63°C for 30sec, 72°C for 1min. 5μl of 5 cycled DNA was taken and quantitative PCR was conducted to optimize PCR cycle (StepOnePlus Real-Time PCR Systems (Thermo Fisher)), and then remaining 45μl was further PCR amplified according to the necessity. DNA was purified with SPRI AMPure XP beads (Beckman, sample to beads ratio 1:2) and eluted in 20μl 10mM Tris HCl pH8.