Frozen tissue was ground into powder and homogenized with buffer A (15mM Tris-HCl PH 8.0, 15 mM NaCl, 60 mM KCl, 1mM EDTA, 0.5mM EGTA, 0.15mM Spermine, 0.5mM Spermidine, 0.5mM DTT, 1mM PMSF with proteinase inhibitors). After cells were lysated, nucleuses were collected, counted and re-suspended in Dnase buffer. 10U Dnase I (New England Biolab) was used to digest 10 million nucleuses at 37C0 for 5 minutes followed by proteinase K digestion. Genomic DNA was then purified. 50 bp and -100 bp DNA fragments were selected for further library construction and sequencing. Libraries were prepared for sequencing using standard Illumina protocols.