Researchers from the University of North Carolina (UNC) at Chapel Hill have sequenced the genome of the nearly indestructible tardigrade, the only animal known to survive the extreme environment of outer space, and found something they never expected: that tardigrades get a huge portion of their genome - nearly one-sixth or 17.5 percent - from foreign DNA. "We had no idea that an animal genome could be composed of so much foreign DNA," said co-author Bob Goldstein, Ph.D., faculty in the biology department in UNC's College of Arts and Sciences. "We knew many animals acquire foreign genes, but we had no idea that it happens to this degree." Tardigrades are water-dwelling, eight-legged, segmented micro-animals. The new work, published online on November 23, 2015 in PNAS, not only raises the question of whether there is a connection between foreign DNA and the ability to survive extreme environments, but further stretches conventional views of how DNA is inherited. The artivcle is titled “Evidence for Extensive Horizontal Gene Transfer from the Draft Genome of a Tardigrade.” First author Thomas Boothby, Ph.D., Dr. Goldstein, and collaborators revealed that tardigrades acquire about 6,000 foreign genes primarily from bacteria, but also from plants, fungi, and Archaea, through a process called horizontal gene transfer - the swapping of genetic material between species as opposed to inheriting DNA exclusively from parents. Previously, another microscopic animal called the rotifer was the record-holder for having the most foreign DNA, but it has only about half as much as the tardigrade. For comparison, most animals have less than one percent of their genome from foreign DNA.
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