Japanese Research Team Discovers The First Virus of Non-retroviral Origin In Our Genome

8% of our genome consists of processed retroviruses. These are remnants of ancient infections which swept through our ancestor’s population. Yet a Japanese research team found something different lurking deep in our chromosomal landscape and which seems to enter a pact with our genetic makeup.

In brief – this is what happened toward the end of the Eocene with our grand-grandparents:

It was a bornavirus, a special kind of RNA virus (quite different from the retroviruses). It invaded our ancestors 40 or so million years ago. The penetration of the immune defense systems was swift and efficient. The invasion of tissues and organs – massive. It reached without particular difficulties the germ cell lines. A retroviral element (even more ancient genomic hitchhiker) ensured the proper integration of its main structural protein together with the flanking regulatory sequence in our DNA. Once part of our genome it started to propagate together with us through the eons of time. But it was not silent – the viral control program become activated and some of the integrated viral proteins started to be expressed and interact with the rest of our ancestors genes. Most of these interactions led to nothing or may be they were even deleterious but a very few actually did work and the evolution decided to keep these successful combinations. In that way the ancient virus actually contributed to our evolution and our being as human creatures becoming part of our genetic networks (something which the retroviruses were exploiting already for hundreds of millions of years).

Here is one of the integration sites of the bornavirus in our genome. On the picture you can see small fragment of human chromosome 3. Under it in different colors are shown and the corresponding genomic sequences of other species (please notice that there is a gap in the non-primate mammals – the integration of the virus occurred 40 million years ago when the separation of primates from the rest of the mammals already have occured):

Click the image above to enlarge and one more time in the lower left corner to enlarge even more.

For the original Nature paper (from 7th of January 2010) please click here.

And this is a link to the picture above but interactive. I created it in UCSC Genome Browser – the Ichiban genome browser out there!