Ancient viruses hide in genetic 'dark matter'
11 May 2012 by qwwqdccwwm.d qwwqdccwwm.d
Scientists have uncovered important information about the ‘dark matter’ of our genomes, revealing clues as to how they became riddled with viruses.
More than 90% of every mammal’s genome has no known function, and much of this ‘dark matter’ is known to harbour bits of DNA from ancient viruses which infected our ancestors as far back as the age of the dinosaurs. Researchers wanted to know why, and searched the genomes of 38 mammals covering a large range of genetic species – including rat, mouse, bat, human, elephant and dolphin – using in silico screening.
The team – which include researchers from the University of Oxford, the Aaron Diamond AIDS Research Centre in New York and Rega Institute in Belgium – used mathematical models to compare the genetic material from all the residing viruses they had collected.
One particular group of viruses had lost the ability to infect new cells – their genetic material could still amplify itself, but their whole life cycle passed within a single cell. This was followed by a dramatic proliferation of the virus’ genetic material within the genomes. Comparison with all the other viruses in the genomes revealed this was a universal phenomenon and that loss of cell infectivity is associated with a 30-fold increase in the abundance of the virus.
“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 the spread massively within it,” said Robert Belshaw from Oxford’s Zoology department.
This pattern resembles that seen in epidemic outbreaks – a small proportion of infected people are responsible for most of the spread of an infectious agent to the rest of the population. These people are known as superspreaders.
“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,” said Dr Gkikas Magiorkinis, lead author of the study published in Proceedings of the National Academy of Sciences.
“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,” added Belshaw.
