According to a recent international study, fragments of ancient viral DNA once considered "junk" may in fact play a role in regulating our genes.
Using an innovative method to trace the evolutionary history of viral DNA, researchers from McGill University and Kyoto University discovered previously overlooked sequences in genomic annotations.
"If we can clearly determine which parts of our genome are unique to humans or primates, and which come from viruses, we will take a step closer to understanding what makes us human, and how DNA influences our health status and the emergence of diseases," explains Guillaume Bourque, one of the study's lead authors and a professor in the Department of Human Genetics at McGill University.
Approximately 8% of the human genome comes from viruses that infected our ancestors millions of years ago. While these sequences were once considered useless, we now know that some of them are involved in turning genes on and off.
The new study, which uncovers specific sequences with regulatory potential, adds to the growing body of evidence that these long-neglected sequences may play an important role and should therefore be studied more closely.
A new method to decode viral DNA
During the sequencing of the human genome 25 years ago, researchers did identify viral DNA, but they lacked the tools to study it in detail. The team therefore re-examined the genome using modern techniques and found that many annotations were outdated or incorrect.
The scientists developed a new method that groups viral sequences based on their evolutionary history, rather than solely on their similarity. By tracing the evolution of sequences over time, they observed patterns that suggest which ones might act on gene activation and deactivation.
Thus, in a family of viral DNA called "MER11", the team discovered that there were not three subtypes, as previously thought, but four. One of these subtypes, MER11_G4, particularly active in human stem cells, contained a specific DNA motif present only in humans and chimpanzees. It is this group that, according to the research team, may play a role in turning genes on and off.
"Current annotation of viral DNA in the genome should not be considered final. It is time to review and refine it," says Guillaume Bourque.
A better understanding of the genome, he adds, could help scientists understand genetic mutations linked to cancer and rare diseases.