Science1 publisher2 min readPublished
Cornell biologists find a human brain gene that kept its ability to jump around the genome
Cornell researchers report that BC200, a gene that appears to work in human neurons, can still jump around the genome, the first human gene seen doing both. The team found it through a copy lodged in a human poxvirus, apparently picked up from infected human cells.
The Scientist · Science desk
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What happened
- The virus is molluscum contagiosum; skin cells are the only cells it is known to infect, so the team thinks BC200 entered it during a skin infection.
- BC200 exists only in humans and closely related primates and evolved from a transposon millions of years ago.
- Roughly half the human genome is transposon-derived DNA, but most of it is inactive and only a very small fraction can still copy itself.
- The gene also turns up at low levels in sperm and eggs, so any new insertions it makes could in principle be inherited.
- It is abnormally expressed in some tumors and found at elevated levels in the brains of people with Alzheimer's disease.
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Why it matters
- contradiction Cornell's 'first' depends on both traits, and the release states them with different confidence: Feschotte calls the cellular function clear, while the same release calls BC200's physiological role uncertain.
- precedent If the inference holds, transposons moving from hosts into viruses, documented so far in a handful of other species, would have a human example with a human skin virus as the recipient.
- constraint The tumor and Alzheimer's findings measure how much BC200 is made; on their own they cannot show that its ability to move contributes to either disease.
"Genes that come from transposable elements and that are repurposed for cellular functions are typically no longer transposable," said Cedric Feschotte, a senior author of the study, which was published Sept. 24 in Science [9][1]. "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." [10]
Mobility is the risky half of that pairing. Transposons can insert stretches of DNA into genes and interfere with how those genes work, sometimes contributing to disease [14]. Over evolutionary time, the same activity can also regulate existing genes or supply material that becomes new ones [14].
Scientists first identified BC200 in the late 1980s as a highly abundant non-coding RNA in human neurons [12]. Abundance suggests a job without naming it. The job the release points to is regulatory: evidence suggests BC200 may help control how neuronal messenger RNAs are translated into proteins [11].
An early precedent for a transposon reaching a virus comes from the same decade. Researchers working with cultured moth cells watched a transposon move from those cells into a baculovirus, a virus that infects insects [13]. That transfer was caught as it happened, in a dish. The BC200 transfer is inferred from its result, the copy found in the poxvirus [3].
I think an element found only in humans and close primate relatives, turning up inside a virus genome, is good evidence that BC200 moved into the virus at some point [5][3]. The skin-cell route is a sensible inference from where the virus is known to grow [4]. The release does not describe the experiments showing that BC200 still moves, how often it does so, or whether skin cells make the RNA at all.
What to watch
- Whether BC200 is caught actively jumping in breast cancer or other tumor cells, and whether those insertions create mutations.
- Whether molluscum contagiosum virus uses its BC200 copy to manipulate the human cells it infects, which Feschotte said the team wants to investigate.