Cornell researchers say a human gene associated with brain cells has turned up inside a poxvirus, offering a rare example of genetic material moving from a person into a virus. The finding, reported by Cornell, concerns BC200, a gene that originated from a so-called jumping gene but appears to have retained the ability to move.
The study was published Sept. 24 in the journal Science. Researchers found two insertions of BC200 in the genome of molluscum contagiosum virus, which infects human skin and can cause warts. They estimate the transfers happened about 100,000 years ago, rather than during a recent outbreak.
A gene with an unusual history
Jumping genes, or transposable elements, are stretches of DNA that can copy or insert themselves elsewhere in a genome. Many have lost that ability over evolutionary time. BC200 is unusual because it appears to be both mobile and used by human cells, according to the Cornell team.
The researchers traced BC200's origin to a transposable element incorporated into a common primate ancestor roughly 40 million years ago. BC200 is found in humans and related primates and is expressed most strongly in neurons, though its exact function in the body remains poorly understood.
Evidence suggests BC200 may help regulate how neuronal messenger RNA is translated into proteins. It also appears at low levels in sperm and eggs, a feature that could allow some new insertions to be inherited. Neither possibility establishes what the gene does in the virus.
Cedric Feschotte, a Cornell molecular biology and genetics professor and senior author of the study, said genes repurposed from transposable elements usually stop moving. BC200 appears to have kept that capacity while taking on a cellular role, he said.
A discovery revisited years later
Co-author Cheng Sun first spotted BC200 in the viral genome in 2010 while studying human transposons in virus databases at the University of Texas at Arlington. The team recognized the finding but did not publish it then. Sun and graduate student Pu Gao later revived the project; Gao is the paper's first author.
The discovery adds to a small number of documented cases of mobile genetic elements crossing into viruses. Earlier research found an insect transposon entering a virus in laboratory cell cultures and a vertebrate transposon embedded in a rodent poxvirus in the wild. The Cornell-led study identifies a human gene in a virus that infects people.
Because molluscum contagiosum virus infects skin cells, the team suspects the transfers occurred there. The study does not show that BC200 changes the virus's behavior or that the virus can carry it into another species. Researchers plan to test whether the virus uses the gene to affect infected cells.
BC200 is also expressed abnormally in some tumors and at elevated levels in the brains of people with Alzheimer's disease. Those observations do not establish that its movement causes either condition. Feschotte said the team wants to investigate whether BC200 jumps within cancer cells and, if so, whether those insertions cause mutations.
The work was supported by the National Natural Science Foundation of China, the University of Texas at Arlington and Cornell. Ellen Pritham, formerly of the University of Texas at Arlington, was among the co-authors.
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