Your DNA holds the blueprint to build your body, but it’s a living document: Adjustments to the design can be made by epigenetic marks. Cataloguing these marks and how they work is important for understanding biology and genetics—and coming up with therapies to address diseases and disorders.
In humans and our fellow eukaryotes, two principal epigenetic marks are known. But a team from the University of Chicago-affiliated Marine Biological Laboratory has discovered a third, novel epigenetic mark—one formerly known only in bacteria—in small freshwater animals called bdelloid rotifers.
This fundamental and surprising discovery is reported Feb. 28 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 Marine Biological Laboratory’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.”
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 by turning genes on or off, particularly during early development or when your body is under stress. They can also suppress transposons, or “jumping genes” that may threaten the integrity of your genome.
This discovery marks the first time that a horizontally transferred gene—that is, a gene acquired from another organism not through sexual reproduction—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.