Neural tube (caudel to midbrain), telencephalon, or limb tissues from E12.5 mouse embryos, or pancreata from E17.5 embryos were dissected and placed in Buffer A (15 mM HEPES pH 7.6, 60 mM KCl, 15 mM NaCl, 0.2 mM EDTA, 0.5 mM EGTA, 0.34 M sucrose) on ice. Nuclei were liberat All libraries were made according to Illumina’s ChIP-seq DNA sample prep protocol