10,000 cells were sorted into collection buffer (PBS, 0.5% BSA, 2mM EDTA), pelleted and lysed in hypotonic buffer (10mM Tris-HCl (pH 7.5), 10mM NaCl, 3mM MgCl2, 0.1% NP-40). Nuclei were pelleted by centrifugation for 30 min. at 500g, 4oC. ATAC-seq adapted from Buenrostro et al., 2013 and Lara-Astiaso et al., 2014. Nuclear pellets were re-suspended in 5uL of transposition mix (1uL Tagment DNA Enzyme, 2.5uL Tagment DNA Buffer from Nextera DNA Sample Prep Kit, 1.5uL H2O), and incubated at 37C for 60min. Two sequential PCR reactions were performed. After the first PCR, libraries were selected for small fragments (< 600bp) using SPRI beads followed by a second round of PCR with the same conditions, and a final SPRI bead purification to capture all fragments for the final library.