ATAC-seq was performed as previously described (Buenrostro et al. 2015) with minor changes. In brief, 50,000 cells were lysed and fragmented using Tn5 transposase (Illumina). Next, the samples were purified using the MinElute kit (Qiagen). The transposased DNA fragments were amplified and purified using the PCR Cleanup kit (Qiagen).