Two 6-well transwell plates of day 17 differentiated hESCs were sonicated for 2 min x 90 % pulse x 5 times using Ultrasonic 3000 Ultrasonic homogenizer (Biologics, Inc). For ChIP-seq, libraries were prepared using the Solexa ChIP-seq DNA Sample Prep Kit (IP102-1001). After amplification, DNA fragments between 180 and 400 bp were gel extracted and sent for sequencing. Libraries were sequenced by the Genome Institute of Singapore using the Illumina Genome Analyzer II as single-end 35 bp reads