Here’s what you’ll learn from reading this story:
• Researchers have identified a gene that combines never-before-seen characteristics in a single gene.
• This “jumping gene,” which also plays a role in brain function, can copy itself and insert itself elsewhere in the genome – and it has appeared in troubling places, including in diseased cells.
• This is the first human gene known to be mobile and also appears to perform a normal cellular function – and it even escaped into a poxvirus.
The BC200 gene has been known for decades, but a new examination of its behavior raises many questions, and not all the answers are encouraging. For the first time, researchers have discovered that this “jumping gene” appears to play an important role in human neurons even as it continues to copy itself to new locations, including, at one point in modern human history, the genome of a human poxvirus.
Writing in the September 24 issue of Sciencea team from Cornell University, Capital Normal University in Beijing, and the University of Texas at Arlington concluded that the mixture of BC200 traits had never been documented in a gene before. The gene, they concluded, “blurs the boundary between gene and transposon, combining stable function with persistent mobilization, including a recent escape in a human poxvirus.”
A transposon, better known as a jumping gene, has an unusual ability: It can copy itself to a new location in the genome, and if it lands inside an existing gene, it can disrupt the normal functioning of that gene, sometimes causing disease. But transposons can also use their powers for positive purposes; Over millions of years, the researchers write, they can be domesticated to become useful regulators of other genes. In fact, the team noted, transposons make up about half of all human DNA, although the vast majority has long since become inert and only a tiny fraction remains mobile. What scientists had never seen before was a human gene that was both mobile and necessary for cellular function. The BC200 changes that.
“Genes that originate from transposable elements and are repurposed for cellular functions are generally no longer transposable,” Cédric Feschotte, a professor in Cornell’s Department of Molecular Biology and Genetics and senior author of the study, said in a statement. “The BC200 itself was created from a moving element but retained its mobility, and yet it also clearly performs a cellular function. Somehow, evolution hasn’t been able to disentangle these two things.”
However, the exact nature of this cellular function remains unclear. BC200 was first described in the late 1980s as a noncoding RNA in human neurons, and the leading theory holds that it helps regulate the translation of neuronal messenger RNAs into proteins. The gene is also expressed at low levels in germ cells (think sperm and eggs), meaning any new copies it makes there could be passed on to future generations.
Taken together, the results suggest that at some point, over millions of years, BC200 acquired a cellular role without ever losing its ability to copy and paste itself into the genome.
This persistent mobility is the troublesome part. By searching genomic databases, the team found two copies of BC200 housed in the genome of molluscum contagiosum (MCV), the largely benign poxvirus behind the wart-like skin bumps of the same name. Since skin cells are the only cells that MCV is known to infect, researchers suspect that’s where the transfers took place. The gene also appears abnormally in certain tumors, including breast cancers, and at high levels in the brains of people with Alzheimer’s disease, “suggesting that its jumping ability may also play a role in these diseases,” according to the release.
The research team now hopes to better understand BC200 and its possible contributions to disease, particularly if the gene enters the genome of cancer cells and creates mutations there.
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