DNA was extracted followed by bisulfite treatment for library preparation. Libraries were prepared according to Illumina's instructions accompanying the TruSeq DNA Methylation Kit (Part# EGMK81312). Briefly, Bisulfite converted DNA was annealed with random hexamer with tagging sequence. DNA copy was synthesized using TruSeq DNA Methyl Polymerase. Then Exonuclease I was used to digest excess random primer. The 3' ends of the strands are then selectively tagged with a second specific sequence tag to generate di-tagged DNA using DNA polymerase. The di-tagged DNA with known sequence tags at both ends was cleaned up by the AMPureXP Beads. The dsDNA library was generated by PCR amplification with Illumina primers for 10 cycles and library fragments of ~350 bp (insert plus adaptor and PCR primer sequences). The library was purified by the AMPureXP Beads. The purified DNA was captured on an Illumina flow cell for cluster generation. Libraries were sequenced on the HiSeq 2500 following the manufacturer's protocols.