Bone marrow cells were collected from the femurs and tibiae of 7 week old mice. Cells were stained with antibodies and cells belonging to each population sorted using a FACS Influx5 (BD Biosciences) 500 cells were sorted directly into individual wells of a PCR tube containing PBS. Assay for transposase-accessible chromatin using sequencing (ATAC-seq) was performed as previously described (Buenrostro et al (2013) Nat. Methods 10:1213). Pooled libraries were run on an Illumina HiSeq 2500 sequencer. RNA libraries were prepared for sequencing using Illumina Nextera DNA preparation kit