Embryos were fixed with 2% formaldehyde for 30 min and quenched with 0.1 M Tris pH7.5. Lysates were sonicated with a microtip sonicator to shear the DNA. Genomic DNA (Input) was prepared by treating aliquots of chromatin with RNase, proteinase K and heat for de-crosslinking, followed by ethanol precipitation. For each ChIP reaction antibody was first incubated overnight at 4 C then Protein A agarose beads were incubated overnight at 4 C. Immune complexes were washed, eluted from the beads with SDS buffer, and subjected to RNase and proteinase K treatment. Crosslinks were reversed by incubation overnight at 65 C, and ChIP DNA was purified by Qiaquick (Qiagen) extraction. Illumina sequencing libraries were prepared from the ChIP and Input DNAs by the standard consecutive enzymatic steps of end-polishing, dA-addition, and adaptor ligation. After a final PCR amplification step, the resulting DNA libraries were quantified and sequenced on NextSeq 500.