Scientists discovered a new form of DNA modification that could carry inheritable information in insects, worms, and algae.
Most DNA modifications occur through methylation, which is a chemical process that has the ability to change gene expression and regulate function-producing proteins, the University of Chicago reported. Organisms can sometimes use epigenetics to bypass the genetic code and transmit traits to offspring; DNA modifications are responsible for driving these transmissions without changing the DNA sequence.
"The human genome is not static. It contains dynamic DNA modifications that carry key inheritable epigenetic information passed among generations of cells," said Chuan He, the John T. Wilson Distinguished Service Professor in Chemistry and a Howard Hughes Medical Institute Investigator.
Genetic information is encoded in DNA's chemical bases: "adenine, cytosine, guanine, and thymine." In the past, researchers thought methylated cytosine was the dominant DNA modification dominant DNA modification in eukaryotes, which is a taxonomical classification encompassing "mammals, insects, worms, plants, and algae." This new study identified an adenine DNA methylation that also epigenetically regulates cellular function in worms, flies, and green algae.
"The conservation of this modification from simple unicellular eukaryotes to vastly different worms and flies indicate its wide presence and functional roles," He said. "All three studies together uncover a potential new epigenetic mark on eukaryotic DNA. They open a new field of biology and chemical biology."
Worms and flies were not known to contain DNA methylations, but the presence of N6-methyladenine (6mA) in green algae was discovered decades ago; despite its discovery the phenomenon has remained generally unstudied until now.
"Genes that have methylated cytosine have been associated with reduced gene expression," said Laurens Mets, associate professor in molecular genetics & cell biology at UChicago. "What's different about adenine methylation is that it is associated with more strongly expressed genes. It's a missing piece in the puzzle of regulation at the DNA modification level, and that's an exciting thing."
The researchers identified a "sharply periodic" pattern of adenine methylation that is linked to the primary structural feature of the nucleus of eukaryotic cells. This feature is a protein complex referred to as a nucleosome, which can be found anywhere in DNA excluding highly expressed genes. These finding provide insight into which factors lead to the precise positioning patterns of nucleosomes.
"We found not only a new DNA modification that affects gene expression, it interestingly marks for active gene expression," He said, cytosine methylation usually marks for repressive gene expression.
Three papers on the subject were published in a recent edition of the journal Cell.