Wednesday, July 7, 2010

Bats and Wallabies Maintain "Fossil" Genes from Filovirus Family

Researchers at the University of Buffalo in a recent publication, "Filoviruses are ancient and integrated into mammalian genomes" in the journal BMC Evolutionary Biology demonstrated for the first time that mammals have harbored filoviruses for at least ten million years, in stark contrast to the currently estimated thousands of years.

Findings by a trio of biologists at UB reveal that modern marsupials harbor a "fossil" copy of a gene that codes for filoviruses, of which Ebola and Marburg hemorrhagic fevers viruses are the most well known.

The study suggests these species maintained a filovirus infection without negative health consequences, and have selectively maintained these so-called "fossil" genes as a genetic defense. Even marsupial species that have never colonized Africa, have had association with filoviruses.

The UB co-authors say that if the rarely captured genes represent antiviral defenses or genomic scars from persistent infections, then the work opens up new possibilities for identifying reservoir species for filoviruses, which harbor the virus but remain asymptomatic.

"The reservoir for filovirus has remained a huge mystery," says Jeremy A. Bruenn, PhD, UB professor of biological sciences and co-author. "We need to identify it because once a filovirus hits humans, it can be deadly."

When the UB researchers studied samples from the fur of a wallaby at the Buffalo Zoo and a brown bat caught on the UB campus, they found that the genomes of both animals as well as some other small mammals contain "fossil" copies of the gene for these deadly viruses, and thus could be candidate reservoir species for them.

The research also demonstrates a new mechanism by which different species of mammals can acquire genes, through non-retroviral integrated RNA viruses, which the UB scientists had previously identified in eukaryotes but was unknown in mammals.

The UB scientists note that it is well-known that RNA retroviruses, like HIV-AIDS, can be integrated into mammal genomes.

"But because filoviruses infect only the cytoplasm of cells and not the nucleus and because they have no means of making DNA copies that might be integrated into the genome -- as retroviruses do -- it was never thought gene transfer could occur between non-retroviral RNA viruses and hosts," says Bruenn. "This paper shows that it does and it may prove to be a far more general phenomenon than is currently known."

"Our findings demonstrate that filoviruses are, at a minimum, between 10 million and 24 million years old, and probably much older," says Taylor. "Instead of having evolved during the rise of agriculture, they more likely evolved during the rise of mammals."

Lance D. Presser has a PhD in Microbiology & Immunology, and is a Public Health Laboratorian.

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