A gene active in human brain cells has turned out to be something biologists did not think existed: a piece of DNA that still works as a functional gene while also retaining the ability to jump around the genome. Researchers led by Cornell University report the finding in a study published Sept. 24 in the journal Science, which also traces two copies of the gene hiding inside the genome of a common human virus.
The gene, called BC200, is a short stretch of non-coding RNA expressed mostly in neurons, where evidence points to a role in regulating how messenger RNA is translated into proteins at nerve synapses. It descends from an ancient "jumping gene," or transposon, that was co-opted for this neuronal job roughly 40 million years ago in an early primate ancestor. Transposons make up close to half of human DNA, but the vast majority have been permanently disabled; genes that take on an essential cellular role are normally stripped of their ability to move. BC200 appears to be an exception, retaining enough mobility machinery to still insert new copies of itself elsewhere in the genome, according to the Cornell Chronicle's summary of the work.
A Virus as a Getaway Vehicle
The team, led by senior author Cedric Feschotte, the Barbara McClintock Professor of Molecular Biology and Genetics at Cornell, found the clearest proof of that mobility in an unexpected place: the genome of molluscum contagiosum virus, a common poxvirus that causes benign skin bumps. Two separate copies of BC200 turned up embedded in viral genomes, insertions the researchers estimate occurred independently about 100,000 years ago — not during a recent outbreak, but a reminder that the gene has hopped before. First author Pu Gao and co-authors Cheng Sun of Capital Normal University in Beijing and Ellen Pritham, formerly of the University of Texas at Arlington, collaborated on the analysis, which was supported in part by the National Natural Science Foundation of China along with Cornell and UT Arlington.
"BC200 was created from a mobile element but retained mobility while serving cellular functions. Evolution hasn't untangled these two things," Feschotte said, calling the viral insertions "the first clear example of a transposon escaping host genome to hop onto a virus."
The discovery adds a wrinkle to a disease picture that remains unsettled. BC200 shows up at abnormal levels in some tumors and is overexpressed in the brains of people with Alzheimer's disease, but the Science paper does not establish that the gene's mobility — or its mere presence — causes either condition; those associations are observational, and the researchers themselves describe BC200's exact physiological role as still uncertain. Whether the gene actively jumps within living human neurons, and whether that movement carries any health consequence, has not yet been tested directly.
Feschotte's group says the next step is probing how BC200's dual identity is maintained at the molecular level and whether related mobile elements elsewhere in the genome have quietly kept the same split function. For now, the finding stands mainly as a reminder that the genome's most heavily studied "junk" DNA can still hold working parts nobody expected to find.
