DNA methylation refers to the addition of a methyl group to the 5-position of cytosine residues that are followed immediately by a guanine (so-called CpG dinucleotides). Small stretches of DNA known as CpG islands are rich in CpG dinucleotides.
These CpG islands are frequently located within the promoter regions of human genes, and methylation within the islands has been shown to be associated with transcriptional inactivation of the corresponding gene. Changes in DNA methylation profiles are common features of development, and DNA methylation is also involved in X-chromosome inactivation and allele-specific silencing of imprinted genes. Aberrant changes in methylation profiles are associated with many serious pathological consequences such as tumorigenesis.
Methylation of CpG islands has been shown to be important in transcriptional repression of numerous genes that function to prevent tumor growth or development. This phenomenon includes both genome-wide hypomethylation and genespecific hypermethylation. Capillary electrophoresis has been applied to the evaluation of the relative methylation degree of genomic DNA methylation.
In this approach, genomic DNA is enzymatically hydrolyzed to single nucleotides. Single nucleotides are then labeled with a fluorescent marker and separated by CE to identify cytosine and 5-methyl cytosine residues.
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