ChIP was performed using anti-OTX2 (R&D#AF1979) E12.5 CD1 GEs were fixed in 1.5% formaldehyde for 20 min. and neutralized with glycine. Fixed chromatin was lysed and sheared into 200-1000 bp fragments using a bioruptor (Diagenode). Immunoprecipitation (IP) reactions were performed in duplicates using Goat IgG as negative controls.A 3rd Replicate was performed omitting IgG as negative control. Precipitated fractions were purified using Dynabeads (Invitrogen). Libraries were prepared using an Ovation Ultralow DR Multiplex System (Nugen), size selected in the range of 200-300 bp on a LabChip (Lifesciences), quality control tested on a Bioanalyzer (Agilent) and sequenced on a HiSeq (Illumina). ChIP-seq (1x50bp reads, 6 samples/lane)