A piece of human DNA has turned up inside a common skin virus, and it is revealing something scientists had not seen before: a human gene that does a job in our cells and can still jump around the genome. The finding, published Sept. 24 in the journal Science, centers on a gene called BC200 and the molluscum contagiosum virus, a human poxvirus, according to Cornell University.

About half of the human genome is made of transposons, often called jumping genes. Nearly all of them are dead, broken copies or have been domesticated into fixed roles. BC200 is different, the researchers report, because it has kept its ability to move.

That raises a practical question. BC200 is overactive in some cancers, and scientists now want to know whether it is jumping in those tumors.

A Working Gene That Kept Its Mobility

Transposons are stretches of DNA that can copy or move themselves to new places in the genome. Over millions of years, they have shaped how genomes evolve, sometimes providing raw material for new genes.

The idea that genes can move was once controversial. Geneticist Barbara McClintock discovered jumping genes in corn in the 1940s and was awarded the Nobel Prize in Physiology or Medicine in 1983. Feschotte now holds a Cornell professorship named for her.

Most human transposons today are inactive. Their copies have accumulated mutations that broke the machinery they once used to move, or cells silence them to protect the genome. A small number of element families remain active and occasionally insert themselves in new places.

BC200 began that way. The gene descends from a mobile element that was co-opted about 40 million years ago in a common primate ancestor, Cornell said. Today it is expressed mainly in neurons, where it is thought to help regulate how messenger RNA is translated into proteins. BC200 does not code for a protein itself. It produces a short RNA molecule, which is why it was named for brain cytoplasmic RNA about 200 nucleotides long.

Cornell molecular biologist Cedric Feschotte described what sets it apart. "BC200 was itself created from a mobile element but has retained its mobility and yet it is also clearly serving a cellular function," he said.

Usually, a jumping gene that gets put to work loses its ability to move, because random insertions could disrupt the genome. BC200 appears to have kept both traits.

Stolen by a Skin Virus

The evidence came from an unexpected place. Researchers found BC200 sequences inside the genome of molluscum contagiosum virus, which causes small, wart-like bumps on the skin and is common in children.

According to Cornell, the team first noticed human transposon sequences in the virus while searching viral genomes in 2010. Further work showed BC200 had jumped into the virus independently at least twice, and the researchers estimate those events happened within the span of modern human history.

For BC200 to end up in a virus, it had to move on its own and insert itself into the viral DNA during an infection. That makes the virus a kind of fossil record proving the gene was still mobile in humans in the recent evolutionary past.

The study was led by Cornell's Feschotte with Cheng Sun of Capital Normal University in Beijing and Ellen Pritham, formerly of the University of Texas at Arlington. Graduate student Pu Gao was first author.

Questions About Cancer and the Brain

BC200 is abnormally active in some tumors, including breast cancer, and has been found at elevated levels in the brains of people with Alzheimer's disease, Cornell said. Those are associations. The study does not show that BC200 causes either disease.

The new question is whether BC200 is actually jumping in cancer cells where it is overexpressed. If so, new insertions could disrupt other genes and contribute to how tumors change over time. Researchers have not yet tested this, and the idea remains a hypothesis.

ScienceDaily noted that BC200's exact physiological role in neurons remains uncertain. Researchers also plan to study whether the virus uses the stolen human sequence to manipulate infected cells.

For people with molluscum contagiosum, nothing changes. The infection is usually mild and clears on its own, and this research does not alter how it is diagnosed or treated.

Genomes as Records of Ancient Encounters

Viruses and their hosts constantly swap genetic material. Human DNA carries fragments of ancient viruses, and viruses can carry pieces of their hosts. Tracking those exchanges lets scientists reconstruct events that left no other trace.

Phys.org also covered the study, which adds a new case in which the direction ran from human to virus and preserved evidence of gene movement that would be hard to detect in the human genome alone.

The work also challenges a tidy rule in genetics: that genes either move or work, but not both. BC200 suggests the boundary between parasitic DNA and useful DNA can be blurrier than expected.

Molluscum contagiosum virus is a useful witness because it infects only humans. Any human DNA found inside it must have been picked up from people, which makes the timing and direction of the transfer easier to interpret.

The study is peer-reviewed, but it describes a single gene and a single virus. Whether other human genes have kept similar mobility is unknown. The bottom line: a human gene hidden in a skin virus shows that at least one working gene can still jump, and the next step is testing whether that ability matters in cancer.

What Readers Want to Know

What is a jumping gene?

A jumping gene, or transposon, is a stretch of DNA that can copy or move itself to new places in a genome. About half of human DNA comes from them.

What is BC200?

BC200 is a human gene expressed mainly in brain cells. It descends from a jumping gene and appears to have kept the ability to move.

How did human DNA end up in a virus?

BC200 inserted itself into the molluscum contagiosum virus during human infections, at least twice, according to the researchers.

Why does this matter?

It is the first known human gene that both serves a cellular function and can still jump, challenging the idea that genes do one or the other.

Is BC200 linked to cancer?

It is overactive in some tumors, including breast cancer, but the study does not show it causes cancer. Researchers want to test whether it jumps in tumors.

Does this affect molluscum contagiosum treatment?

No. The infection is usually mild, and the finding does not change diagnosis or treatment.