For cultured neurons, cells were fixed on plate with 1% formaldehyde, nuclei were isolated and then sonicated by bath ultrasonicator (Bioruptor). Lysates were clarified and DNA-histone complexes were isolated by either anti-H3K4me3 (Active motif 39159) or H3K27ac (Active motif 39133) immobilized by protein A dynabeads (Life). Purified DNA was prepared for sequencing with the TruSeq ChIP sample Prep Kit (Illumina) as per manufacturer's instructions. Libraries were sequenced on either HiSeq2000 (Illumina) with 50bp single reads or NextSeq500 with 75bp single reads.