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UT Arlington researchers find 'space invader' DNA infiltrated mammalian genomes

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Wednesday, October 22, 2008

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Media Contact: Sue Stevens

ARLINGTON - News of research done by a team of genome biologists at The University of Texas at Arlington has traveling around the world faster than the speed of light. Since being posted in The Proceedings of the National Academy of Sciences online early edition on Oct. 20, a paper by Assistant Professor of Biology Cedric Feschotte; John K. Pace II, a graduate student; Clement Gilbert, post doctorate fellow; and Marlena S. Clark, a former UT Arlington undergraduate researcher, has been already been featured in the New Scientist and in newspapers and online news services of Argentina, Brazil, China, Germany and Russia.

The story is garnering broad international interest because it provides the first robust evidence for the “horizontal transfer” of a mobile genetic element in a wide range of vertebrates, including several mammals. Horizontal transfer occurs when an organism incorporates genetic material from another organism without being the offspring of that organism. Mammals normally obtain genes “vertically”– handed down from parents and grandparents. Bacteria receive theirs in this way too, but also "horizontally" – passed from one unrelated individual to another or even between different species.

Feschotte and his colleagues have found the first unequivocal evidence that this horizontal gene transfer also has occurred in mammals, reptiles and amphibians, including the bush baby (a nocturnal primate), little brown bat, rats and mice, opossum, tenrec, green anole lizard and African clawed frog. The horizontal transfer was facilitated by a kind of "parasitic" DNA found in cells, known as a transposon. Feschotte says that what he calls "Space Invader" tranposons jumped sideways millions of years ago into several species, possibly by piggybacking onto a virus. The transposon then integrated itself into the chromosomes of germ cells, ensuring that it would be passed onto future generations. This means that some parts of the mammal's DNA do not descend from its direct ancestors, but was acquired laterally from a distantly related species.

“The same transposon infiltrated the genome of a wide range of vertebratesfive mammals, one frog and one lizardall around the same time, around 30 million years ago,” Feschotte said. “Based on paleontological records, we know that some of these species or their direct ancestors inhabited different continents, like the tenrec in Africa and the opossum in America”

Feschotte said these results imply that somehow the transposon was able to travel across continents, possibly by “hitchhiking” onto a virus with a broad host range that was spreading around the world at that time in a pandemic.

The discovery, if confirmed, will literally change scientific understanding of evolution, according to a story in The New Scientist, the world's leading online science and technology news service.

This is one of those studies that raises more questions than it answers, Feschotte said. But one thing is clear, he continued: the transfer of the “space invader” transposons was not a mere anecdotal event for the species that suffered their infiltration, but had important consequences for genome evolution. The researchers found that the initial infiltration of the transposon was followed by its explosive amplification within the genome of each of the species, independently spawning many thousands of transposon copies throughout their chromosomes. For example, they found 100,000 copies in the tenrec genome alone. Thus Feschotte and co-workers concluded the process must have had a strong influence on the evolutionary trajectories of these species and contributed to what make them genetically different.

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