Viral DNA has been in the mammalian genome for more than 40 million years

[steven johnson]

A newly discovered source of mammalian DNA involves retroviruses that have been inserting genetic material for the past 10s of millions of years. This has apparently affected mammalian evolutin.

Bornaviruses, a type of RNA virus that causes disease in horses and sheep, can insert their genetic material into human DNA and first did so at least 40 million years ago, the study shows. The findings, published January 7 in Nature, provide the first evidence that RNA viruses other than retroviruses (such as HIV) can stably integrate genes into host DNA. The new work may help reveal more about the evolution of RNA viruses as well as their mammalian hosts.

In the new study, Japanese researchers found copies of the bornavirus N (for nucleoprotein) gene inserted in at least four separate locations in the human genome. Searches of other mammalian genomes also showed that the gene has hitched rides in a wide variety of species for millions of years.

Retroviruses make up about 8 percent of the human genome. When these viruses insert into the genome, the result is usually bad for the host. But not always: Some retrovirus proteins can help fight off infection with other retroviruses. And at least twice in primate evolution retrovirus insertions have added genes to the host genome that aid in making the placenta. Now those proteins are essential for placenta development, says Cédric Feschotte, an evolutionary geneticist at the University of Texas at Arlington. It is not clear what role, if any, the EBLN-1 and EBLN-2 genes play in humans.

He (Feschotte) speculates that bornavirus could be another source of human mutations, especially in neurons. Some studies have linked infection with the virus to psychiatric disorders such as schizophrenia. Feschotte thinks modern bornaviruses may worm their way into human DNA in the neurons, creating mutations in genes that could lead to schizophrenia.

Bornavirus genes found in human DNA

[theoldman]

1. I think this goes back before primates evolved.

It would therefore effect a lot of animals other than humans.

[cutlassmama]

2. Yes, mammals