Human Genome Contains Pieces of DNA From Ancient Dinosaur Era Viruses

Posted on April 28, 2012

More than 90% of every mammal's genome has no known function. This part of genetic material is sometimes called "dark matter." It contains pieces of DNA from ancient viruses. There are thought to be thousands of these endogenous retroviruses integrated into human DNA and some of them can be traced as far back as the dinosaur era.

Researchers at Oxford University, the Aaron Diamond AIDS Research Center in New York and the Rega Institute in Belgium wanted to know how these ancient viruses got into their hosts' genomes in such abundance. The researchers searched the genomes of 38 mammals covering a large range of species including mice, rats, bats, humans, elephants and dolphins. Genetic material from all of the residing viruses was collected and then compared using mathematical models.

The findings revealed that one particular group of viruses had lost the ability to infect new cells. Their genetic material is still able to amplify itself but the whole lifecycle of the virus is passed within a single cell. This change, they found, was followed by a dramatic proliferation of the virus' genetic material within the genomes. The pattern resembles that which we see during epidemic outbreaks, whereby a small proportion of infected people (superspreaders) are often responsible for most of the spread of an infectious agent to the rest of the population.

According to the lead author, Dr Gkikas Magiorkinis from Oxford University's Zoology Department, says, "We know that much of the 'dark matter' in our genome plays by its own rules, in the same way as an epidemic in an infectious disease, but operating over millions of years."

Robert Belshaw, also from Oxford's Zoology Department, who led the study, says, "We suspect that these viruses are forced to make a choice: either to keep their 'viral' essence and spread between animals and species, or to commit to one genome and then spread massively within it. This is the story of the epidemic within every animal's genome, a story which has been going on for 100 million years and which continues today."

The findings were published here in the journal, Proceedings of the National Academy of Sciences.

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