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May 5, 2015 | by Justine Alford
DNA, the genetic material of all living things, is what makes us who we are. Written in this molecular code are the instructions for making proteins, which are the building blocks of cells and thus living organisms. In natural circumstances, this code is formed of four basic units, or “letters”: A, C, G and T (adenine, cytosine, guanine and thymine). These so-called DNA bases pair up, A with T and C with G, forming a long, readable sequence that varies from gene to gene. Textbooks will tell you that it is those four letters that are the recipe for life, or so we long believed.
Back in the ‘80s, scientists threw another base into the mix: 5-methylcytosine (mC). As the name suggests, mC is cytosine with a functional unit called methyl attached. But it was not for another decade that scientists realized the importance of mC: The addition of methyl groups to DNA can switch genes on or off in order to meet the needs of each tissue, given that every cell contains the same DNA sequences. Such modifications are known as epigenetic changes; these allow the environment to affect gene expression, but they also play a role in various diseases. For example, alterations in mC have been shown to contribute to the development of cancer, amongst many other conditions.
But it turns out that the DNA alphabet does not even end here, as in recent years scientists have gradually expanded this list to eight. Now, scientists have just detailed descriptions of one more potential candidate, N6-methyladenine (6mA), in the journal Cell. As with mC, this is composed of the base adenine with a methyl group tacked onto it. While scientists have known about this modified base for some time, it was thought to have exclusively existed in bacteria, where it serves to protect against the unwanted addition of foreign DNA from other organisms.
Now, a group of researchers from IDIBELL-Bellvitge Biomedical Research Institute have found that this is not the case, providing evidence that 6mA is not simply a phenomenon of primitive cells. As described in the journal Cell, scientists found that some more complex cells, called eukaryotic cells, also possess the base. Eukaryotes are organisms within one of the three domains of life, the others being archaea and bacteria.
More specifically, researchers discovered 6mA in three different groups of eukaryotes: green algae, flies and worms. This was made possible through the development of highly sensitive analytical techniques, which picked up the exceedingly low levels of this base that previously eluded detection. Interestingly, newly gathered data indicates that, like mC, 6mA may also have a gene regulatory function in these animals, which could suggest that it also behaves as an epigenetic mark.
Now that scientists have found this base in various organisms, the researchers want to scrutinize our own genomes to see if it also exists in humans. This would be interesting given the fact that evidence seems to suggest that 6mA may play a role in stem cells. If it does indeed exist in our own species, then researchers may have a job on their hands trying to figure out what precise role it plays in the cell.
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