mESC or neuronal cells on 100mm plates were cross-linked with 1% formaldehyde for 10 min while shaking at room temperature and rinsed three times with cold phosphate-buffered saline. Cells from five plates were pooled and harvested in phosphate-buffered saline with protease inhibitors by 10 min centrifugation at 4C. All ChIP assays were performed with 112 μg of chromatin and 3 μg of FGFR1, RXR, Nur77 or H3.3 antibodies using the Invitrogen MAGnify ChIP Kit according to manufacturer's instructions with slight modifications. Genomic DNA was precipitated with ethanol, treated with RNase A and proteinase K, and purified using the Qiagen PCR purification kit Chromatin was further prepared using the Tru-seq ChIP Sample Preparation Kit and purified library DNA was captured on an Illumina flowcell for cluster generation and sequenced on an Illumina Hisequation 2000, following the manufacturer's protocols.