title: A systematic evaluation of whole genome amplification of bisulfite-modified DNA.
abstract: BACKGROUND
  Studying DNA methylation profiles in detail should be the first step in epigenetic research. Although sodium bisulfite modification of genomic DNA is the gold standard method for DNA methylation analysis, this method results in the loss of the majority of the DNA material. Whole genome amplification (WGA) of bisulfite-modified DNA is expected to provide a rich source of materials, but its validity has not been thoroughly evaluated. In this study, we evaluated the extent of biased amplification in the WGA of bisulfite-modified DNA and the reproducibility of independent WGA reactions. We performed the multiple displacement amplification-based WGA separately three times. Each experiment included two reactions using 10 or 50 ng of bisulfite-modified DNA as template. DNA methylation levels were compared between WGA products and original bisulfite-modified DNA at about 450,000 CpG sites.
  
  
  RESULTS
  Using a sufficient amount of bisulfite-modified DNA for WGA was critical for downstream application. The considerable deviations from original bisulfite-modified DNA were found in the middle range of DNA methylation levels. Distribution of hyper- and hypomethylation were equal, which suggested that the deviation at each CpG site occurred randomly. Averaging the data from independently amplified WGA products dramatically improved the overall quality.
  
  
  CONCLUSIONS
  WGA of bisulfite-modified DNA could be a valuable tool for epigenetic research, but careful experimental design and data interpretation are required.
authors.affiliation: Department of Molecular Psychiatry, Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8655, Japan. kaziwamoto-tky@umin.ac.jp.
authors.forename: Miki
authors.initials: M
authors.lastname: Bundo
authors.forename: Fumiko
authors.initials: F
authors.lastname: Sunaga
authors.forename: Junko
authors.initials: J
authors.lastname: Ueda
authors.forename: Kiyoto
authors.initials: K
authors.lastname: Kasai
authors.forename: Tadafumi
authors.initials: T
authors.lastname: Kato
authors.forename: Kazuya
authors.initials: K
authors.lastname: Iwamoto