library_construction_protocol: ATAC-seq was performed following the Omni-ATAC protocol (Corces et al. 2017), that has been shown to reduce the number of mitochondrial reads while increasing the signal-to-noise ratio. 25,000 cells were collected, lysed for 3 min on ice in lysis buffer (10mM Tris-HCL pH.5, 5M NaCl, 1M MgCl2, 0.1% NP-40, 0.1% Tween-20, 0.01% Digitonin), washed in wash buffer (10mM Tris-HCL pH.5, 5M NaCl, 1M MgCl2, 0.1% Tween-20), and spun down at 500 RCF at 4°C for 10 min. Pellets were resuspended in 50 µL of transposition reaction (2X TD buffer, 1X PBS, 0.1% Tween-20, 0.1% Digitonin, 5µL of Illumina Tn5 transposase) and incubated for 30 min at 37°C with 1,000 rpm agitation. DNA was isolated with Zymo DCC5 kit and eluted in 21 µL of elution buffer. DNA samples were initially amplified by 5 cycles of PCR, followed by a variable number of additional amplification cycles estimated by qPCR for each sample. PCR products were purified using the Zymo DCC5 kit and eluted in 20 µL of H2O. A two-size selection of fragments was performed using 0.5x and 1.3x volume of AMPure XP beads (Beckman Coulter). Libraries were quantified and analyzed using Qubit and Tapestation assays, before preparing equimolar dilutions. Paired-end sequencing was performed on NextSeq 500 (Illumina).