Genomic DNA of iPSCs (~4 × 10^5) was purified using an All Prep DNA/RNA mini kit (QIAGEN) following manufacturer's guidelines. Whole Genome Bisulfite Sequence (WGBS): Unmethylated lambda phage DNA (1/200 of the estimated gDNA mass) (Promega) was spiked into the samples, and then the samples were subjected to bisulfite conversions and library constructions for amplification-free WGBS analyses (Miura et al., 2012).