DNA-Methylation Analysis by the Bisulfite-Assisted Genomic Sequencing Method

The postreplicative methylation of DNA at the C5 position of cytosines is found in a broad spectrum of organisms ranging from prokaryotes to human (1 ). In prokaryotes the major role of cytosine C5 methylation (like adenine N6 and cytosine N4 methylation) is to protect the genome against DNA degrading nucleases (restriction/modification), whereas in many eukaryotes cytosine C5 methylation (found within CpG dinucleotides) plays a pivotal role in the control of gene expression, inactivation of repetitive sequences, stability of chromosomes, and in cell transformation leading to development of cancer. The growing evidence that the cytosine methylation is also crucial in embryonic development of mammals regulating genomic imprinting, X inactivation and cell differentiation (2 ) has caused a demand for effective methods that would detect this modification with high sensitivity and reliability.