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About 106 million years ago, when the world was totally dominated by the dinosaurs and our mammalian ancestors lived hidden in burrows, a virus managed to integrate into the genome of one of them. And just two million years later, history repeated itself and another virus, closely related to the first, did the same. Now, a team of biologists from the University of Oxford has just found the remains of these viruses inside our own cells.
In the words of Aris Katzourakis, co-author of the research, “they are kind of hidden, hidden from view in the human genome“. These authentic ‘viral fossils’ they could be, according to the researchers, the oldest discovered so far.
The work has just been published in
bioRxiv.
full of fossil viruses
It may sound strange, but the human genome is literally chock-full of fossil viruses. There are so many that, according to estimates, between 5% and 10% of our entire genome consists of precisely this class of remnants of ancient viruses. Most of them are retrovirus, specialized in creating copies of their RNA genes in the genomes of the cells they infect. And when that happens in cells that give rise to eggs and sperm, those copies can be passed down from generation to generation.
Over time, however, the genes of these viruses mutate until finally they are no longer capable of giving rise to more viruses and their remains, already inactive, remain embedded in the genome.
two different viruses
But the two newly discovered viruses are different. To begin with, it is not about retroviruses, but about ADN virusspecifically from an old group of viruses called Mavericks. Its fossil remains have been found in various types of animals, such as fish, amphibians or reptiles, but never in mammals.
According to the researchers, however, these two viruses in particular must have been a plague for mammals from the moment they began to evolve, about 180 million years ago, in the Jurassic, until at least 105 million years ago. , in the Cretaceous, when viruses began to insert themselves into genomes. After that time, the Mavericks seem to die out in mammals for reasons that are still unclear, although they continued to affect fish and other types of animals.
“There are not that many non-retroviral viruses in our genome,” says Katzourakis. “This is the only DNA virus in the human genome that we know of, and it is certainly the oldest non-retroviral insert in our genomes.”
Of course, other even older viral insertions may have occurred, but their fossil remains may have been lost, or perhaps have mutated so much that they are unrecognizable.