library_construction_protocol: EB or MEF cells were harvested as described above. ChIP assays for ETV2 and H3K27ac were performed from 2 x 106 MEFs or 1 x 107 EB cells, respectively. Briefly, cells were crosslinked with 1% formaldehyde for 10 min at room temperature and the reaction was quenched by glycine at a final concentration of 0.125 M.  For the BRG1 ChIP-seq, cells were first crosslinked in 2 mM disuccinimidyl glutarate (DSG; Life Technologies: Cat. #20593) for 30 min then in 1% formaldehyde for 10 min, quenched with glycine for 5 min.  The remainder of the ChIP protocol was performed following the protocol described by Magli et al19. We used antibodies against H3K27ac (Abcam, ab4729), ETV2 (Abcam, ab181847), and BRG1 (Abcam ab110641) for the respective pulldowns. For both of the pulldowns, protein A Dynabeads were added to the ChIP reactions and incubated for 30 minutes at room temperature. Magnetic beads were washed and chromatin was eluted. After crosslinking reversal, RNase A, and proteinase K treatment, ChIP DNA was extracted with the Min-Elute PCR purification kit (Qiagen). ChIP DNA was quantified with Quant-it PicoGreen dsDNA Assay Kit (Life Technologies). Sequencing libraries were prepared using equal amount of ChIP DNA per sample as per instructions of SMARTer® ThruPLEX® DNA-Seq Kit (Takara R400675) and SMARTer® DNA Unique Dual Index Kit - 24U Set A (Takara R400665). Sequencing was performed at the University of Minnesota Genome Center with the The NextSeq 550 high-throughput benchtop sequencer. ChIP-seq libraries were prepared for sequencing using standard Illumina protocols