Scientists catch a human brain gene still jumping around our DNA

A working human brain gene is still moving around the genome, and two copies of it just turned up inside a human poxvirus.

BC200 is a small noncoding RNA active mainly in neurons, where it helps regulate translation, the step where cells read RNA into protein. About half of the human genome is made up of DNA that arrived from transposons, genetic elements that move and copy themselves, and most of those elements went quiet millions of years ago. BC200 did not. A team led by Cedric Feschotte at Cornell University reports in Science, published Sept. 24, that BC200 has stayed mobile across roughly 40 million years of primate evolution and that two BC200 copies have turned up inside the genome of molluscum contagiosum virus (MCV), the poxvirus that causes a common skin infection.

BC200 was co-opted about 40 million years ago to do a job in neurons, and it kept its mobility. Across primate evolution, the Cornell team reports, BC200 has acted as a "master source" of L1-mediated retrotransposition, a process in which the cell's L1 machinery copies the gene back into the genome at new locations. Hundreds of lineage-specific insertions trace back to BC200 as their original source, and the same paper documents BC200-derived insertions that are still polymorphic in modern humans, meaning some people carry them and others do not.

Two separate BC200 sequences have been identified inside the MCV genome, and MCV is the only poxvirus known to infect only humans. The insertion sites in the virus carry the signature of L1-mediated retrotransposition, which suggests the human gene was copied into the viral genome while the virus was replicating inside a human cell.

That makes MCV the first documented case of a working human gene being carried inside a human-specific poxvirus, the kind of cross-species transfer that has been suspected for decades but is rarely caught in the act. Poxviruses are a large family that includes smallpox and the vaccine used to eradicate it, and they are unusual among viruses in doing most of their replication outside the nucleus, in the cell's cytoplasm. That should, in principle, make it harder for host RNA to be reverse-transcribed and inserted into viral DNA, which is what makes the MCV finding a clean counterexample.

Cedric Feschotte, the paper's senior author, framed the result as an evolutionary puzzle rather than a new rule. "The mobility and the function are not at odds, they coexist," he said. "That's what makes this an interesting puzzle to study."

There are real limits to the new claim. It rests on a single study, and the authors themselves describe the MCV finding as the first example of its kind, not the first rule. About half of human DNA is transposon-derived, but only a tiny fraction still moves. BC200 sits in that small minority, and it is one gene, in one virus, on one paper. The dating of the 40-million-year co-option depends on evolutionary comparisons across primate genomes, which carry their own assumptions, and the full text of the paper was not independently reviewed here for methodological detail.

The next question is whether the same pattern shows up elsewhere. If BC200 can ride out into a poxvirus, the same machinery might have done it before with other genes, and other human-specific pathogens could be carrying pieces of us. The paper is the first clear case; whether it is the first of many is the watch item.

For now, the human genome looks less like a finished blueprint and more like a working draft, still being edited in neurons, in the germline, and occasionally, when the right virus is in the right cell, across the species line.