“Space Invader” Genetic Elements Colonized Mammalian & Reptile Genomes 15 -46 Million Years Ago.

By Yidir K. Published on October 22, 2008 12:30
space Invader

Foreign genetic elements have integrated themselves into the genomes of several mammalian and reptilian species via horizontal transfer, rather than by traditional vertical inheritance, according to a new report.

Cédric Feschotte of the University of Texas at Austin and colleagues discovered previously uncharacterized elements of the hAT (hobo/Activator/Tam3) transposon superfamily, which they dubbed "space invaders." Feschotte says that what he calls space invader tranposons jumped sideways millions of years ago into several species by piggybacking onto a virus.

In most organisms, genes are inherited or passed along from parent to offspring. Lateral or horizontal transfer of genetic information, which is central to the evolution of simple prokaryotic organisms, occurs when non-native genetic elements incorporate themselves into a host genome. These elements are typically delivered via viruses, circular loops of DNA called plasmids, or transposons, which are small sequences of mobile DNA.

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The researchers discovered the elements while surveying DNA transposons in the bushbaby, a nocturnal primate, and, after further examination, found the invaders in other species, including rats and mice, opossum, and the African clawed frog. Space invaders were not present, however, in the genomes of many other vertebrate species. These infiltrations, the authors say, are the first report of horizontal transfers of transposons in mammalian species, and likely occurred around the same time frame in affected species approximately 15 to 46 million years ago.

Feschotte says he expects many more reports of horizontal gene jumping. "We're talking about a paradigm shift because, until now, horizontal transfer has been seen as very rare in animal species. It's actually a lot more common than we think."

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The team thinks that the hAT transposon invasion occurred about 30 million years ago and spread across at least two continents. "It's like a pandemic, and one that can infect species that weren't genetically or geographically close. It's puzzling, scary almost," Feschotte said in an interview with New Science.

It may not be a coincidence that the time of the invasion coincides with a period in evolutionary history that saw mass mammal extinctions. This is usually attributed to climate change, Feschotte says, but it is not off the map to suppose that this type of invasion could contribute to species extinction.

The hAT transposon does not occur in humans, but some 45% of our genome is of transposon origin.

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Feschotte's work on the hAT transposon is the first time that a "jumping gene" has been shown to have entered mammalian genomes, and the first time it has been shown to do so in at around the same time, in a range of unrelated species, in different parts of the world.

Casey Kazan.


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