The most common
type of epigenetic change is the methylation of specific cytosine bases. Thanks to
the efforts of Shankar Balasubramanian and his colleagues from the
University of Cambridge and from the Babraham Institute, there is now a way to
see exactly where these methylation changes occur.
A methyl group is simply a carbon atom attached to three
hydrogen atoms. The carbon atom can form a fourth bond to whatever is being
methylated, in this case a cytosine. The result is 5-Methylcytosine (5mC) (shown to the left). Highly methylated regions of the genome are associated with lower levels of gene expression. Therefore, finding these regions can tell us a lot about which genes are turned on.
Briefly, the researchers found that they could change 5mC into uracil in a series of steps by the addition of specific enzymes. By using different reagents to sequence the same strand of DNA, the could distinguish which bases had originally been 5mC.
Briefly, the researchers found that they could change 5mC into uracil in a series of steps by the addition of specific enzymes. By using different reagents to sequence the same strand of DNA, the could distinguish which bases had originally been 5mC.
Why
is this so exciting? As I mentioned, gene expression is tightly linked to
epigenetic changes. Unfortunately, ordinary DNA sequencing cannot detect these
changes. Imagine being able to determine
which genes were turned off in a cell you just pulled out of a specific organ. Or being able to compare
epigenetic changes before and after administering a drug. We would be able to
follow gene expression under all kinds of conditions. I expect a great many
uses to come from this new technique.
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