After cross-linking in 1% formaldehyde in PBS for 30 minutes, tissues were rinsed and treated with trypsin for 5 minutes to generate a single cell suspension. Samples were then pre-disrupted with a Branson 450 Sonifier, and then sheared with a Bioruptor (Diagenode) to generate a chromatin size range of 200–600 bp. PureProteome Protein G Magnetic Beads (Millipore) were pre-incubated with H3k27ac antibody before incubating overnight with 100-200 μg of sheared chromatin. After washing, immune complexes were eluted from the beads, and protein-DNA crosslinks were reversed by incubating at 65˚C overnight. After treatment with RNase followed by proteinase K, samples were purified with the QIAquick PCR Purification Kit (Qiagen). ChIP and input chromatin control libraries were produced using the NEBNext ChIP-Seq Library Prep Master Mix Set for Illumina (New England BioLabs) as directed by the manufacturer with Illumina-compatible adapters. Libraries were sequenced with 50 bp single-end runs on an Illumina HiSeq 2000 at the HudsonAlpha Institute for Biotechnology.