Embryos were aged to the desired stage, as confimed by DAPI staining and microscopy.

Staged tissue was fixed using 1% formaldehyde for 10 minutes at room temperature. Tissue was then homogenized and filtered through a 60 micron nitex membrane. Nuclei were pelleted at 4500g for 20 minutes then resuspended and disrupted using bead-beating with 2mm tungsten beads. Chromatin was then sonicated to a size range of 500 bp to 2 kb. Soluble chromatin was recovered after centrifugation at 15000g for 5 minutes.