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.”Marine Biological Laboratory, “New DNA modification system discovered in animals, captured from bacteria more than 60 MYA” at ScienceDaily (February 28, 2022)
The obvious question this raises is, what about all the detailed Darwinian narratives that a horizontal gene transfer could obviate?
The paper is open access.
You may also wish to read: Horizontal gene transfer: Sorry, Darwin, it’s not your evolution any more.