A human brain gene that never stopped jumping
Cornell researchers found BC200, a human gene with an essential role in neurons that still carries its ancient ability to move through DNA, embedded inside a poxvirus that infected human skin.
Biologists have long worked from a tidy assumption: when a gene gets repurposed from one of the genome’s wandering elements and picks up an essential job, it settles down. A gene doing real work in the cell, the thinking goes, can no longer afford the risk of leaping to a new location — the way an employed person stops impulse-moving across the country. Researchers at Cornell University have now found a human gene that breaks that rule. BC200 plays an important role in brain cells while still retaining the ability to jump around the genome, making it the first known human gene to combine an essential physiological function with the mobility of a transposable element.
The story begins millions of years ago, when BC200’s ancestor was a transposon — one of the mobile DNA sequences that make up a startling share of our genome and have spent evolutionary time copying and pasting themselves from place to place. Plenty of human genes descend from these elements, and the standard account is that domestication tames them: once a transposon-derived sequence starts earning its keep, selection locks it in place and the jumping machinery decays. BC200 apparently never got that memo.
The evidence for its restlessness comes from an unlikely place. The Cornell team found BC200 embedded inside molluscum contagiosum virus, a human poxvirus — the first known example of a human gene that is both mobile and required for bodily functions turning up as a stowaway in a virus that infects human skin. The most straightforward explanation is that the gene jumped out of an infected skin cell and into the virus’s genome, a literal demonstration that BC200 can still move. Genes don’t end up inside poxviruses by staying put.
What makes this especially odd is that BC200 is not genomic dead weight. It is expressed mainly in neurons and may help regulate protein synthesis — which is to say, it does a genuine job in one of the most exacting cell types in the body. A gene that both matters enough to be conserved and jumps often enough to land inside a virus sits awkwardly against the usual framing, in which function and mobility are a trade-off rather than a package deal.
There is a real question underneath this about what else the assumption might be hiding. If biologists have been filtering out mobile-but-functional genes because they expected domesticated transposon descendants to be immobile, BC200’s discovery suggests the filter was leaking. One example doesn’t overturn the trade-off story, but it does mean the search for others can now proceed on the premise that they exist.
It’s also just a striking image: a gene doing quiet, essential work in your neurons, and simultaneously capable of hitching a ride inside a poxvirus. Evolution usually resolves that kind of tension by picking a side. In BC200’s case, apparently, it never did — and the cell has been living with the arrangement for millions of years.