Tardigrade DNA Analysis Reveals A Whole Genetic Arsenal Used To Make Them Almost Indestructible

Scanning electron microscope image of the hydrated tardigrade, Ramazzottius varieornatus. Tanaka S/Sagara H/Kunieda T

Josh Davis 20 Sep 2016, 17:33

Tardigrades are known to be one of the hardiest animals in the world. Found in every environment, from the tops of mountains to the bottom of the ocean, the tough little moss piglets can even survive the vacuum of space. In an attempt to explain how the critters are able to manage this amazing feat researchers have scoured the animal’s genes, and may have found some clues.

By sequencing the genome of the Ramazzottius variornatus tardigrade, one of the hardiest known species, the team of scientists from the University of Tokyo was able to identify certain characteristics unique to the water bears that may be important in protecting them against the extreme stress of the environments in which they live. One of the most prominent discoveries was of a protein termed “Dsup” that is unique to tardigrades, and seems to have a role in protecting DNA against damage.

“Dsup can protect DNA from radiation as well as oxidative stress in human cultured cells and even conferred improved radiotolerance on human cultured cells,” explained Takekazu Kunieda, who co-authored the study published in Nature Communications, to IFLScience. “This clearly demonstrates that the tolerability can be transferred to other animal cells by [introducing] tardigrade-unique genes. Our tardigrade genome sequence contains many tardigrade-unique genes and these could be a bountiful source for new protection genes and mechanisms.”

Not only have they found that Dsup is unique to the water bears, but they have also found a whole host of other genetic clues to their ability to survive extreme stress. The creatures' DNA also contains more copies of anti-oxidant enzymes and a DNA repair gene, which may help fight damage caused by oxidants like free radicals, as well as a few copies of oxidative enzymes that could themselves degrade DNA. It seems then that the tardigrades have a whole genetic arsenal at their disposal to protect themselves against their environment.

Yet this latest peek at the water bear’s genome has revealed something else. While an earlier study reportedly found that almost one-sixth of the tardigrades' DNA is composed of foreign genes, suggesting a remarkable amount of genetic transfer among species, this latest study refutes that. Follow-up experiments had already found that the massive amount of foreign DNA detected in the earlier study was actually due to heavy contamination of the samples.

“They did not perform effective cleaning before sampling and several following studies indicated that most of the detected [horizontal gene transfer] genes are highly likely derived from contaminating microorganisms not included in tardigrade genome,” Kunieda told IFLScience. After meticulously cleaning their own samples to make sure they were as pure as possible, and then using the same technique employed in the first study, Kunieda and his team found that only around 1.2 percent of the tardigrades DNA is from other sources, a fairly unremarkable figure for animals.

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