Viral Infiltration

Some 8% of the human genome comes from viruses that have infected us throughout evolution; contributions from retroviruses have long been known to pepper our genome. Now, researchers in Japan report that a previously unknown source of viral genetic code infiltrated our blueprint about 40 million years ago (Nature, DOI: 10.1038/nature08695).

In particular, genetic information from a bornavirus, an RNA virus that infects the brain and other tissues, was discovered in the genomes of humans, elephants, squirrels, and various other mammals by a team led by Keizo Tomonaga, a virologist at the University of Osaka. The majority of the bornavirus genetic contribution is in noncoding regions of the human genome, but segments similar to a bornavirus gene that codes for a protein resembling the virus's nucleocapsid can be expressed in human cells. "The finding unveils bornaviruses as a potential cause of mutation and also as an unforeseen source of genomic innovation," notes Cédric Feschotte, a biologist at the University of Texas, Arlington, in a commentary of the study. The work also sets the stage to test "the alleged but still controversial" association of bornavirus infection and certain psychiatric ailments, such as schizophrenia and mood disorders, he adds.