What doesn't kill us -- becomes us

The borna virus is at once obscure and grotesque. It can infect mammals and birds, but scientists know little about its effects on its victims. In some species it seems to be harmless, but it can drive horses into wild fits. . .

Some scientists have even claimed that borna viruses alter human behavior, playing a role in schizophrenia and bipolar disorder. . .

The virus now turns out to have an intimate bond with every person on Earth. In the latest issue of Nature, a team of Japanese and American scientists report that the human genome contains borna virus genes. The virus infected our monkey-like ancestors 40 million years ago, and its genes have been passed down ever since.

Borna viruses are not the only viruses lurking in our genome. Scientists have found about 100,000 elements of human DNA that probably came from viruses. . .

Scientists who hunt for these viruses think of themselves as paleontologists searching for fossils. Just as animals get buried in rock, these viruses become trapped in the genomes of their hosts. While their free-living relatives continue to evolve, fossil viruses are effectively frozen in time. . .

Fossil viruses are also illuminating human evolution. Scientists estimate that 8.3 percent of the human genome can be traced back to retrovirus infections.

But this estimate may be far too conservative. And most interesting is the notion that the incorporation of viruses may play an important role in evolution:

Dr. Tomonaga and his colleagues suspect that borna viruses didn’t actually invade mammal genomes. Instead, the genomes kidnapped them. . .

Two of the four copies of the borna virus gene carry crippling mutations. It’s impossible for our cells to make proteins from them. But the other two genes look remarkably intact, perhaps suggesting that our bodies use them for our own benefit. Exactly what they do isn’t clear though.

Studies on other captive viruses have revealed that some help ward off viral invasions. One virus protein, syncytin, is essential for our being born at all.

From the NY Times.

Posted by David on January 13, 2010 8:41 AM