Embryos were homogenized and fixed in 1.8% formaldehyde at room temperature. After several washes, chromatin in lysis buffer was sonicated to a length range of 0.1kb-0.5kb. For each immunoprecipitation, sheared chromatin was precleared with Gammabind G agarose coated with BSA and incubated with pre-absorbed rabbit anti-Grh antibody, mouse anti-Grh antibody or rabbit IgG. Precipitated complexes were washed, eluted, and cross-links were reversed at 65°C. After Proteinase K treatment, DNA was purified using QIAprep Spin columns and recovered in 50 μl of elution buffer containing RNase A. DNA libraries were made using the Illumina ChIP-seq library kit