In humans and other eukaryotes, two principal epigenetic marks are known. A team has discovered a third, novel epigenetic mark — one formerly known only in bacteria — in bdelloid rotifers, small freshwater animals. Epigenetic marks are modifications to DNA bases that don’t change the underlying genetic code, but ‘write’ extra information on top of it that can be inherited along with your genome.

Epigenetic marks are modifications to DNA bases that don’t change the underlying genetic code, but «write» extra information on top of it that can be inherited along with your genome. Epigenetic marks usually regulate gene expression — turn genes on or off — particularly during early development or when your body is under stress. They can also suppress «jumping genes» — transposable elements that threaten the integrity of your genome.

In humans and other eukaryotes, two principal epigenetic marks are known. A team from the Marine Biological Laboratory (MBL) has discovered a third, novel epigenetic mark — one formerly known only in bacteria — in bdelloid rotifers, small freshwater animals. This fundamental and surprising discovery is reported this week in Nature Communications.

«We discovered back in 2008 that bdelloid rotifers are very good at capturing foreign genes,» said senior author Irina Arkhipova, senior scientist in the MBL’s Josephine Bay Paul Center. «What we’ve found here is that rotifers, about 60 million years ago, accidentally captured a bacterial gene that allowed them to introduce a new epigenetic mark that was not there before.» This is the first time that a horizontally transferred gene has been shown to reshape the gene regulatory system in a eukaryote.

«This is very unusual and has not been previously reported,» Arkhipova said. «Horizontally transferred genes are thought to preferentially be operational genes, not regulatory genes. It is hard to imagine how a single, horizontally transferred gene would form a new regulatory system, because the existing regulatory systems are already very complicated.»

«It’s almost unbelievable,» said co-first author Irina Yushenova, a research scientist in Arkhipova’s lab. «Just try to picture, somewhere back in time, a piece of bacterial DNA happened to be fused to a piece of eukaryotic DNA. Both of them became joined in the rotifer’s genome and they formed a functional enzyme. That’s not so easy to do, even in the lab, and it happened naturally. And then this composite enzyme created this amazing regulatory system, and bdelloid rotifers were able to start using it to control all these jumping transposons. It’s like magic.»

«You don’t want transposons jumping around in your genome,» said first author Fernando Rodriguez, also a research scientist in Arkhipova’s lab. «They will mess things up, so you want to keep them in check. And the epigenetic system to accomplish that is different in different animals. In this case, a horizontal gene transfer from bacteria into bdelloid rotifers created a new epigenetic system in animals that hasn’t been described before.»

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Materials provided by Marine Biological Laboratory. Original written by Diana Kenney. Note: Content may be edited for style and length.