Cells control which genes they express by multiple mechanisms, one of which is the direct modification of DNA with small molecules. Methylation of genes effectively silences them, and excess DNA methylation, particularly of genes that control the cell cycle, is known to promote cancer formation. However, it is unclear whether the enzymes that modify DNA in this way target specific genes or whether random modifications select cells for enhanced tumorigenic capactiy.
In new research, Rudolf Jaenisch and colleagues, at the Whitehead Institute in Cambridge, Massachusetts, investigated DNA methylation in a mouse model of colon cancer. They found that a DNA methylating enzyme, Dnmt3b, targeted specific genes for silencing, and that these genes were similar to those silenced in human tumors. In addition, the researchers believe that their results show that aberrant DNA methylation may be one of the initiating events in the development of cancer.
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