Sorted LSKs underwent ATAC-seq. 20.000 sorted LSK cells were initially resuspended in lysis buffer and centrifuged. The nuclei pellets were then subjected to transposition reaction using the Nextera Tn5 transposase enzyme (Illumina). Tagmented DNA was purified with the MinElute PCR Purification Kit and eluted in 10L of elution buffer (Qiagen). Barcoded libraries were prepared and PCR amplified. Double-sided bead purification was performed using AMPure XP beads to remove primer dimers and large >1,000 bp fragments. Libraries were sequenced 50 bp paired end on an Illumina HiSeq 2500.