Evolution repeats itself as viruses become more pathogenic (September 2015)
The latest paper from our group shows how ancient herpesviruses repeatedly captured the same virulence genes from retroviruses. The study reveals an evolutionary mechanism that sheds some light on this question by studying the remnants of ancient viruses. Millions of years ago, an unusual virulence gene was independently captured by herpesviruses from retroviruses twice. Three of these herpesviruses carry this superantigen gene and currently infect South American monkeys and the pygmy rice rat. These viruses are very closely related to human herpesvirus 8 (HHV8), which is known to cause cancer in patients with HIV. Our findings indicate that there is an underlying evolutionary mechanism driving gene acquisitions from retroviruses by herpesviruses that co-infect the same host, as in the case of HHV8 and HIV.
A large fraction of the human genome is made up of endogenous retroviruses left behind by the viruses that infected our ancestors. We share many of these endogenous retroviruses with our chimpanzee relatives, with whom we share a common ancestor ~6 million years ago. We found that while most of these shared endogenous retroviruses behaved like ‘junk DNA’, viruses from a particular group known as HERV-H have been evolving more rapidly than neutral DNA and have been under selection. Some of the more than 1000 HERV-H retroviruses in our genomes are expressed in human stem cells, and we found that viruses that are expressed in human stem cells have changed the most. Perhaps our ape ancestors domesticated some of these retroviral genomic invaders for a functional role in human stem cells. This paper is published in Retrovirology.
Press release for our paper in PLoS Pathogens on how increases in mammalian body size lead to lower retroviral activity, and implications for cancer. This work has been covered by various news outlets including Science , the Independent and Scientific American.
A relative of the Herpesvirus responsible for roseola disease in children, has been found incorporated into the genome of one of our distant cousins, the Philippine tarsier. It is the first case of an integrated herpesvirus, and the largest known ancient virus to be found in a mammalian genome. Our paper on this was published in PLoS Genetics and is covered in the ERV blog.
“Ancient virus DNA thrives in us”, BBC News article by David Shukman.
“Hunting fossil viruses in human DNA”, New York Times article by Carl Zimmer.
Radio interview with Aris Katzourakis by Norman Swan at the Australian Broadcasting Corporation (ABC), which can be heard here.
“I, virus: Why you’re only half human”, article in the New Scientist by Frank Ryan.
“Darwin’s surprise”, article by Michael Specter in the New Yorker. on endogenous retroviruses.