design: For each islet ChIP experiment, islets from at least 10 adult (8-10 week old) ICR (for  transcription factor libraries) or C57 (for histone methylation libraries) were purified by  collagenase digestion and gradient centrifugation, with subsequent hand picking. Liver  samples were obtained and ChIP was performed as described 26 using 3µg of anit-FoxA2  (Santa Cruz), anti-Pdx1 (Upstate), anti-Hnf4a (Santa Cruz), anti-H3K4me1 (Santa Cruz),  anti-H3K4me3 (Santa Cruz), or normal rabbit IgG (Santa Cruz). DNA from triplicate  pooled ChIP experiments was purified by 8% PAGE to obtain 100-300bp fragments and  sequenced on an Illumina 1G sequencer according to Robertson et al