Pro-B cells (Lin–CD19+c-Kit+IgM–IgD–CD25–) were isolated from the bone marrow of Chd4fl/flCd79a-CreTg/+ or wild-type littermate controls using the Synergy Sorter (iCyt). Cells were lysed to extract nuclei. Nuclei were resuspended in 50 μL 1× TD buffer containing 2.5 μL transposase (Nextera, Illumina). The transposase reaction was conducted for 40 min at 37 °C. Library amplification and barcoding were performed using Illumina compatible index primers purchased from IDTdna.com. PCR was conducted for 12-15 cycles. Library purification was performed with the MinElute PCR Purification Kit (Qiagen) and size selection was using AMPureXP beads (Beckman Coulter). Libraries were quantified and size distribution was assessed using the Bioanalyzer High Sensitivity DNA Kit (Agilent). Paired-end sequencing was performed on a HiSeq 2500 (Illumina) with 50 cycles for each read.