In 2009, the DNA alphabet expanded. Scientists discovered that an extra letter or "sixth nucleotide" was surprisingly abundant in DNA from stem cells and brain cells.
Now, researchers at Emory University School of Medicine have mapped the patterns formed by that letter in the brains of mice, observing how its pattern of distribution in the genome changes during development and aging.
Those patterns, stable or dynamic depending on the gene, suggest that 5-hydroxymethylcytosine (5-hmC) has its own distinct functions, which still need to be fully brought to light.
"Our data tells us that 5-hmC is not just an intermediate state," says senior author Peng Jin, PhD, associate professor of human genetics at Emory University School of Medicine. "It looks like it has specific functions in stem cells and brain. 5-hmC may poise a gene to be turned on after being repressed."
The results were published online Sunday by the journal Nature Neuroscience. The paper is the first report on how the patterns of 5-hmC's distribution change in mouse brain during development, and also contains data on 5-hmC in DNA samples from human brain.
Postdoctoral fellow Keith Szulwach and instructor Xuekun Li are co-first authors, and collaborators from the University of Chicago and the University of Wisconsin-Madison contributed to the paper.
5-hydroxymethylcytosine (5-hmC) is an epigenetic modification of cytosine, one of the four bases or "letters" making up DNA. Epigenetic modifications are changes in the way genes are turned on or off, but are not part of the underlying DNA sequence. 5-hmC resembles 5-methylcytosine (5-mC), another modified DNA base that scientists have been studying for decades. Until recently, chemical techniques did not allow scientists to tell the difference between them.
In contrast to 5-mC, 5-hmC appears to be enriched on active genes, especially in brain cells. 5-mC is generally found on genes that
|Contact: Holly Korschun|