A piece of our genetic heritage has been found where no one expected it: in a human virus.
Researchers have discovered two copies of BC200 in the molluscum contagiosum virus, which causes small, generally harmless skin lesions. BC200 is a particular human gene: it produces a molecule found mainly in neurons.
DNA cutting.
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Its history dates back around 40 million years. A mobile DNA element, capable of producing new copies of itself elsewhere in the genome, appeared in the ancestor of several primates. Over time, this sequence became BC200 and acquired a useful function.
Researchers have found hundreds of copies of this gene over the course of evolution in different primates. Some insertions even vary among modern humans.
Yet once a gene becomes useful, its mobility should decrease: it should no longer be able to move around the genome.
Its passage into a virus is particularly interesting. The two copies discovered in the molluscum contagiosum virus do indeed come from humans. According to the study, they were acquired separately during the recent history of our species.
The virus infects skin cells. Researchers therefore think that BC200 ended up in the viral DNA when the virus was using the cellular machinery to multiply. The virus may thus have carried away a genetic fragment directly from its human host before infecting another human.
This discovery also changes how BC200 should be viewed. A gene that has acquired a useful function in the cell was generally considered to be stabilized in the genome. Here, the two properties coexist: BC200 performs a biological function and retains its ability to generate new insertions. The boundary between an ordinary gene and a mobile element is therefore becoming less clear.
What BC200 does once installed in the virus remains to be determined. Researchers want to find out whether molluscum contagiosum exploits this sequence to modify the cells it infects. They also plan to investigate its activity in certain cancer cells, where BC200 is abnormally present, to determine whether its movements can produce new mutations.