Formaldehyde was added directly to the growth media for a final concentration of 1% for 10 mins at 37C to initiate chromatin fixation. The entire two-day ChIP procedure was performed using the EZ-Magna ChIP HiSens Chromatin Immunoprecipitation Kit (Millipore 1710460) according to the manufacturer’s protocol. Samples were pulse sonicated with 2 rounds of 10 mins (30s on-off cycles, high frequency) in a rotating water bath sonicator (Diagenode Bioruptor) with 5 mins on ice between each round. To detect histone modifications, antibodies (H3K4me2: Millipore 17-677, H3K4me3: Millipore 04-745, H3K27ac: Millipore 17-683) were optimized individually for each antibody to be 0.5 μL for 1 million cells. 1 μL of IgG (Millipore 12-370) was used for negative control. ChIP samples were prepped with NEBNext Ultra II DNA Library Prep Kit for Illumina (NEB E7645S). DNA libraries were prepared for sequencing using standard Illumina protocols