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Volume 9, Number 9Space holderMarch 4, 2005

Retrovirus struck ancestral primates millions of years ago

The ancestors of chimpanzees and gorillas were infected with a retrovirus about three to four million years ago, but there is no evidence it infected ancestors of modern-day humans, according to research by genome scientists at the UW and elsewhere. The virus struck after humans had split off the evolutionary tree from other primates, researchers said.

The infection may have played a role in the evolution of such great apes as chimps and gorillas. The research appears in the April issue of the journal Public Library of Science-Biology, which is available online now.

Researchers led by Evan Eichler, associate professor of genome sciences, studied portions of the genome containing retro-elements, also known as junk DNA. They found many copies of a gene sequence in the chimp and gorilla genomes that didn't appear anywhere in the human genome. They translated that genome sequence into its corresponding protein, and discovered that it was the remnant of a retrovirus, a virus that copies its genetic information into the host's genome.

Evidence suggests that the retro-element originated from an external retrovirus that actively infected ape species in the past. Researchers think the virus infected and possibly killed off some of the population, but also caused genetic errors in survivors. Those errors could have eliminated more of the population.

Eichler and his colleagues think the virus may have caused a population bottleneck that could have quickly reduced genetic variability in the primate groups. That process may have led to the emergence of the species that became modern chimps and gorillas.

Researchers don't understand why the virus affected the ancestors of chimps, gorillas, and Old World monkeys, but did not seem to affect the ancestors of humans or of Asian apes. Ancestral humans were likely living in the same area of Africa as great apes during that period.

The study's lead authors are Zhaoshi Jiang, a Ph.D. student in Eichler's lab, and Chris Yohn, a technician at Case Western Reserve University in Cleveland.

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