For the first time, scientists have identified a human gene that appears to serve an important biological role while still retaining the ability to move around the genome. Researchers at Cornell University made the discovery after finding a human genetic element inside a poxvirus. Their analysis showed that the element, known as BC200, is not only associated with brain function but also behaves like a jumping gene, meaning it can move and insert itself into genomes.
A study published Sept. 24 in Science reports that BC200 combines traits that scientists had not previously seen together in a human gene. BC200 is expressed mainly in neurons, but its evolutionary history traces back millions of years to a transposon, also known as a 'jumping gene', a non-coding genetic element capable of relocating itself and inserting into new places in a genome. Transposons can sometimes be harmful because they are able to insert stretches of DNA into genes and interfere with normal function, potentially contributing to disease.
Over evolutionary timescales, however, they can also be useful. Their activity can help regulate existing genes or contribute genetic material that eventually becomes part of new and beneficial genes. About half of the human genome is made up of transposon-derived DNA.
Most of these elements are no longer active, and only a very small fraction can still move and copy themselves within genomes. "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. "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." Scientists have documented a handful of cases in other species in which transposable elements moved into viruses. One early example came in the late 1980s, when researchers working with cultured moth cells observed a transposon moving from those cells into a baculovirus, a type of virus that infects insects. BC200, however, is found only in humans and closely related primates.
Scientists first identified it in the late 1980s as a highly abundant non-coding RNA in human neurons. Its exact physiological role remains uncertain, but evidence suggests that BC200 may help regulate how neuronal messenger RNAs are translated into proteins. BC200 also appears at low levels in germ cells - sperm and eggs - which means it may have the potential to create new insertions in the genome that could be inherited by future generations.
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