A gene that breaks the rules
Almost half of human DNA consists of ancient "jumping genes" — restless stretches of genetic material that once copied and pasted themselves around the genome. Nearly all of them have long since stopped moving. But scientists at Cornell University have now identified a remarkable exception: a human gene that is both essential for brain function and still capable of jumping — and that, tens of thousands of years ago, leapt clean out of the human genome and into a virus.
The study, published September 24, 2026, in the journal Science, reports that the gene, called BC200, combines characteristics never before seen together in a human gene. It is primarily active in neurons, where it appears to play an important role in brain function. At the same time, it retains the mobility of the transposable element it evolved from — and the researchers found its fingerprints inside molluscum contagiosum virus (MCV), a poxvirus that infects only humans.
It is, as far as anyone can tell, the first documented case of a human jumping gene naturally escaping into a human virus. And it raises questions that reach from the deep history of our species to the biology of cancer and Alzheimer's disease.
What BC200 is
BC200 is a small gene that produces a noncoding RNA — a molecule made from DNA but never translated into protein. It was discovered in the late 1980s as an abundant RNA in human neurons, and it is found only in humans and our close primate relatives. Although its precise physiological role is still poorly understood, evidence suggests it helps regulate how the brain's messenger RNAs are translated into proteins — a fundamental part of how neurons operate.
BC200 did not start out as a respectable brain gene. It originated millions of years ago from a transposon, the technical term for a jumping gene: a mobile genetic element able to copy itself and insert the copies elsewhere in the genome. Transposons are often dismissed as "junk DNA," and they can be dangerous — inserting a block of DNA into the middle of a working gene can disrupt it and cause disease. But over evolutionary time, they have also been a creative force, occasionally being repurposed into useful functions: regulating genes, assembling new ones, rewiring the genome's circuitry.
The standard story is that once a transposon is domesticated into a functional gene, it settles down. Mobility is lost; utility remains. BC200 refused to follow the script. According to the new research, it has kept copying itself around primate genomes for somewhere between 35 and 55 million years — all while serving its role in the brain.
"Genes that come from transposable elements and that are repurposed for cellular functions are typically no longer transposable. BC200 was itself created from a mobile element but has retained its mobility and yet it is also clearly serving a cellular function. Somehow evolution hasn't been able to untangle these two things." — Cedric Feschotte, senior author of the study, Cornell University
The escape into a virus
The trail began in 2010, when researchers first noticed BC200 sequences inside molluscum contagiosum virus. MCV is a poxvirus that infects human skin, causing small, benign, wart-like bumps — unpleasant but generally harmless, and familiar to dermatologists worldwide.
The new study, led by Pu Gao with senior author Cedric Feschotte — the Barbara McClintock Professor in Cornell's Department of Molecular Biology and Genetics — along with Cheng Sun of Capital Normal University in Beijing and Ellen Pritham, formerly of the University of Texas at Arlington, set out to determine exactly what happened. Their conclusion: BC200 jumped into the virus twice during human history, with the insertions dating to roughly between 25,000 and 158,000 years ago — on the order of a hundred thousand years in the past.
The evidence is striking in its completeness. Every one of the 65 complete MCV genomes in public databases carries a 141-letter stretch copied from the human BC200 gene. Poxvirus genomes are famously ruthless editors, with a deletion rate that should purge anything the virus does not need. For a piece of human genetic material to survive in all of them for tens of thousands of years suggests one of two things: extraordinary luck, or a job. The researchers suspect the latter — that the virus may be using BC200 for its own purposes, perhaps to manipulate the human cells it infects.
Feschotte, who has spent years studying how transposable elements move between genomes and viruses, put the rarity of the event in perspective:
"I think at the time it was the first and only case of a clearly vertebrate transposable element escaping into a virus in the wild." — Cedric Feschotte, Cornell University
There had been earlier documented cases of transposons entering viruses in other species — including, in the late 1980s, a laboratory experiment in which a transposon from moth cells growing in culture inserted itself into a baculovirus that infects insects. But that happened in a dish, under artificial conditions. The BC200 case appears to be the real thing: a natural jump, in the wild, into a virus that infects people.
How the jump probably happened
The researchers believe BC200 most likely made its leap inside skin cells — the only cells known to be infected by molluscum contagiosum virus. The scenario is straightforward enough: the virus infects a skin cell, BC200 RNA is present in that cell, and at some point the genetic element copies itself into the viral genome, hitching a ride that would carry it through thousands of generations of viral replication.
What makes the story more intriguing is that BC200 is not confined to the brain and skin. It is also found at low levels in germ cells — sperm and eggs — which means it is potentially capable of generating heritable insertions elsewhere in the human genome. In other words, this is not a fossilized relic of ancient genome evolution. It is a gene that may still be on the move within us, in the cells that carry our DNA to the next generation.
The team also turned up fresh evidence of that ongoing restlessness: scanning 908 human genomes, they found eight new BC200 insertions — copies that appear to have landed recently enough in evolutionary terms to vary between individuals. The jumping gene, it seems, has not retired.
What it could mean for disease
BC200's double life — brain gene and mobile element — may have consequences for human health. The gene is abnormally expressed in some tumors, and it is overexpressed in the brains of patients with Alzheimer's disease. Those observations raise a provocative possibility: that BC200's retained jumping ability could be contributing to disease, by inserting copies of itself into new genomic locations and disrupting the genes it lands in.
The researchers are careful to frame this as a question, not a conclusion. The next steps, they say, include investigating whether the molluscum virus is actively using BC200 to manipulate its human host cells, and whether BC200 is jumping inside cancer cells and causing the mutations that drive tumors. If the answers turn out to be yes, a gene currently regarded as a curiosity of genome evolution could become a target of genuine medical interest.
There is a broader lesson here too. Transposable elements make up roughly half of human DNA, and for decades they were written off as genomic parasites or junk. The BC200 story is a reminder that the genome is less like a fixed blueprint and more like an ecosystem — with elements that move, adapt, escape into viruses, and occasionally take on jobs nobody assigned them. Understanding that ecosystem, mobile elements and all, is becoming one of the central projects of modern genetics.
The long history of a restless gene
Step back, and the BC200 saga spans an almost geological timescale. Some 35 to 55 million years ago, a jumping gene began copying itself through the genomes of early primates. Along the way, one lineage of copies was domesticated into a brain gene found today only in humans and our primate kin. It kept jumping anyway. Around a hundred thousand years ago — when anatomically modern humans were spreading across the planet — it leapt twice into a skin virus, where its descendants persist in every known genome of that virus. And it may still be jumping in us today.
It is a story that blurs the boundaries we like to draw between our genes and the microbial world around us, between the useful and the parasitic, between the ancient past and the living present. The genome, this research suggests, was never really ours alone — and some of its most interesting residents are still on the move.
Sources
