Genomic DNA was extracted using the Monarch Genomic DNA Extraction Kit (New England Biolabs) following manufacturer's instructions including proteinase K and RNase A incubations. For mice, outer cortical tissue was dissected in cold PBS followed by genomic DNA extraction. For adult turtle kidneys, surface convolutions or medullary tissue were dissected in cold PBS followed by extraction of genomic DNA. Firstly, the genomic DNA spiked with lambda DNA were fragmented to 200-400 bp. The DNA fragments were bisulfite treatedto generate single strand DNA (ssDNA). During the bisulfite conversion, unmethylated cytosine were converted into uracil, whilemethylated cytosine staid unchanged. Methylation sequencing adapters were ligated, followed by double strand DNA synthesis. Thelibrary was ready after size selection and PCR amplification.