DNA methylation

Published on October 1, 2007 Updated on April 2, 2014   51 min

Other Talks in the Series: Epigenetics, Chromatin, Transcription and Cancer

Other Talks in the Series: Eukaryotic Gene Regulation

DNA Methylation, presented by Steve Jacobsen.
Cytosine DNA methylation at the fifth position of the cytosine ring is the most prevalent modification of DNA found in eukaryotic organisms. And DNA methylation is a major determinant of so-called epigenetic gene regulation.
Epigenetics is defined as heritable changes in gene expression which are not associated with changes in the sequence of the DNA. Instead, epigenetic inheritance is based on stable, alternative chromatin architectures at specific loci. DNA methylation plays a major role in epigenetic inheritance, because DNA methylation patterns can be stably inherited from cell to cell during mitosis, and in some cases from generation to generation during meiosis. While there are a few exceptions to this general rule, DNA methylation is usually associated with gene silencing.
DNA methylation is a very ancient phenomenon and in fact evolved first in bacteria as restriction modification systems that serve as a defense against foreign DNA, such as viruses. These methylation restriction systems are composed of specific DNA methyltransferase enzymes that act at short, palindromic sequences and restriction enzymes that cleave this same sequence only if it is unmethylated. In this way, bacteria can distinguish self DNA from non-self DNA. And foreign, incoming, unmethylated DNA can thus be recognized and destroyed. In eukaryotic organisms, DNA methylation has evolved into a mechanism that allows dividing cells to stably inherit states of gene activity. DNA methylation is involved in a great number of epigenetic regulatory processes found throughout all of the major eukaryotic groups, including fungi, plants, and animals.