Nuclei were isolated, quantified, and divided into three tubes for digestion with 25U, 50U, and 75U of DNase I, respectively. DNA was extracted via phenol/chloroform and selectively retained for sizes below 200 bp in a 2% agarose gel. DNase-seq library was prepared with NEBNext Ultra™ II DNA Library Prep with Sample Purification Beads (New England Biolabs)