The viruses within -- and what keeps them there (w/ Video)

January 13, 2010
This shows the functioning of Kap1 protein in mouse embrocation cells. Credit: Pascal Coderay, pascal@salut.ch

It is known that viral "squatters" comprise nearly half of our genetic code. These genomic invaders inserted their DNA into our own millions of years ago when they infected our ancestors. But just how we keep them quiet and prevent them from attack was more of a mystery until EPFL researchers revived them.

The reason we survive the presence of these endogenous retroviruses—viruses that attack and are passed on through germ cells, the cells that give rise to eggs and sperm—is because something keeps the killers silent. Now, publishing in the journal Nature, Didier Trono and his team from EPFL, in Switzerland, describe the mechanism. Their results provide insights into evolution and suggest potential new therapies in fighting another retrovirus—HIV.

By analysing in mice within the first few days of life, Trono and team discovered that mouse DNA codes for an army of auxiliary proteins that recognize the numerous viral sequences littering the . The researchers also demonstrated that a master regulatory protein called KAP1 appears to orchestrate these inhibitory proteins in silencing would-be viruses. When KAP1 is removed, for example, the viral DNA "wakes up," multiplies, induces innumerable mutations, and the embryo soon dies.

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Because retroviruses tend to mutate their host's DNA, they have an immense power and potential to alter genes. And during ancient pandemics, some individuals managed to silence the retrovirus involved and therefore survived to pass on the ability. Trono explains that the great waves of endogenous appearance coincide with times when evolution seemed to leap ahead.

"In our genome we find traces of the last two major waves. The first took place 100 million years ago, at the time when mammals started to develop, and the second about fifty million years ago, just before the first ," he says.

The discovery of the KAP1 mechanism could be of interest in the search for new therapeutic approaches to combat AIDS. The virus that causes AIDS can lie dormant in the red blood cells it infects, keeping it hidden from potential treatments. Waking the virus up could expose it to attack.

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otto1923
not rated yet Jan 13, 2010
I wonder about the other great extinctions. Can a genome get so overloaded with viral DNA that whole groups could die off? Could this indicate a 'lifespan' for an entire species?
Adam
not rated yet Jan 13, 2010
Interesting the "Great Wave" idea, like Greg Bear's SF story "Darwin's Radio" - he based the novel's scenario of sudden species origin on the then work on ERVs, and all findings since have added plausibility to the idea, even if the specific instance he imagines isn't likely.
PinkElephant
not rated yet Jan 13, 2010
Can a genome get so overloaded with viral DNA that whole groups could die off? Could this indicate a 'lifespan' for an entire species?


Two mechanisms work against this. First is mutation: over time, it will tend to disfigure viral genes until they become utterly dysfunctional (which has no effect on the rest of the organism, since those genes are perma-silenced anyway.) Second is recombination errors during meiosis in germ cells: pieces of DNA can be "lost in translation". For instance, the human Y chromosome is expected to completely disappear in the next few million years (if human species survives that long), as vital genes continue to migrate away from it to other chromosomes; it is already a mere shadow of its ancient self...
otto1923
not rated yet Jan 13, 2010
it is already a mere shadow of its ancient self...
Good thing humans show up at just the right time to find a way to fix this-
barakn
3 / 5 (2) Jan 13, 2010
The virus that causes AIDS can lie dormant in the red blood cells it infects, keeping it hidden from potential treatments.

Red blood cells don't have DNA and aren't infected by the AIDS virus. They meant white blood cells.
AnnieG
not rated yet Jan 14, 2010
Consider that the act of capping the HIV virus could actually shut down an evolutionary process which is underway via that very HIV virus.
otto1923
not rated yet Jan 14, 2010
could actually shut down an evolutionary process
Just because it's evolution doesnt mean it's not detrimental or flawed. Nature is not infallible. If this viral detritus is harmful maybe we can fix the process in certain species. Neither death nor extinction have to be inevitable.

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