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Why Tardigrades Are So Indestructible

Tardigrades, or “water bears,” are microscopic animals capable of withstanding some of the most severe environmental conditions — even being "dead" for 30 years, and then restored to life! Research from Japan has now created the most accurate picture yet of the tardigrade genome — and why it matters to humans.

In a study published in Nature Communications, geneticist Takekazu Kunieda and colleagues from the University of Tokyo present a genetic analysis of Ramazzottius variornatus or tardigrade ramazzottius varieornatus, arguably the toughest and most resilient species found in the entire tardigrade clan.

The tardigrades' unique arsenal of strategies to cope with stress, including a protein that protects its DNA from radiation damage, are all revealed.

When researchers transplanted this protein into cultured human cells, the same protections applied — a finding with potential applications to cell preservation methods, genomic therapies, and the burgeoning science of transgenics.

Tardigrades are adorable "bear like" microscopic creatures capable of withstanding some of the worst nature can throw at them. Classified as “extremophiles,” they survive freezing, total dehydration, radiation, even the vacuum of space. They are ancient, having diverged from ancestral animals back in the pre-Cambrian epoch (~600 million years ago), and likely have been evolving their unique genes ever since.

Earlier this year, scientists successfully revived a tardigrade frozen solid for more than three decades — a new record for the species.

Scientists are curious about tardigrades as these ancient creatures could tell us something about alien life on other planets, or just how we might be able to leverage their biology into our own medicine and genetics.

Last year, geneticists from the University of North Carolina at Chapel Hill revealed the tardigrade’s truly bizarre genetics. They identified 17.5 percent of the tardigrade genome comes from other organisms, including plants, fungi, bacteria, and viruses. They felt the "water bear" acquired many of its characteristics not as a result of its own evolution, but through others in a process called horizontal gene transfer.

The new research from the University of Tokyo shows that the vast majority of tardigrade characteristics are “proprietary,” and not the result of horizontal gene transfer.

The new study differed from the previous one in some very important ways. Researchers used one of the most resilient tardigrade species on the planet, R. varieornatus, whereas the previous study looked at Hypsibius dujardini, which is among the least tolerant freshwater tardigrades.

Also, researchers successfully eliminated all extraneous bacteria (using commercial chlorine bleach, and other measures) allowing them to scan the tardigrade genome without contaminants. This is important. The authors of the original study claimed an incredible amount of bacterial genes were included in the tardigrade genome. Also, 2016 researchers sequenced the tardigrade genome at a much higher level of accuracy, creating a genetic profile 100 times less fragmented than in 2015. Looking at the 2016 sequenced genome, scientists observed the proportion of foreign genes is closer to 1.2 percent, much lower than the 17.5 percent claimed in 2015.

The tardigrade genome contains more copies of an anti-oxidant enzyme and a DNA-repair gene than any other animal.

These genes help the tardigrade counteract oxidative stress when it’s dehydrated, allowing it to efficiently repair damaged DNA.

Also, water bears express a tardigrade-specific protein that binds to DNA. Called Dsup, this unique protein shields against x-ray radiation, preventing tardigrade DNA from snapping apart, helping to explain why tardigrades seem impervious to radiation, and why they can survive the vacuum of space.

X-ray tolerance can be transfered into the cells of other animals. On tests using cultured human cells, researchers demonstrated Dsup suppresses x-ray-induced DNA damage by a whopping 40 percent.

Kunieda also feels Dsup isn’t perfect. It reduces the damage done by radiation to DNA by approximately half, “which is significant, but still only half.” What’s more, Kunieda believes tardigrades use other strategies in addition to Dsup to fend off radiation effects.

Still, Kunieda is excited for Dsup and other “extremotolerant” characteristics of tardigrades, both those that have been found and those waiting to be found. “Especially, if dehydration-tolerance can become transferable, I hope it will transform the way we preserve various biological materials, including cells, crops, meats, fish, and so on.”

Although more work needs to be done to fully understand the tardigrade genome — this creature is a survivor, and we would do well to learn its many tricks.

Article adapted from George Dvorsky for Gizmodo

Tardigrades, also known as water bears, are small aquatic animals. Some tardigrade species tolerate almost complete dehydration and exhibit extraordinary tolerance to various physical extremes in the dehydrated state. Here we determine a high-quality genome sequence of Ramazzottius varieornatus, one of the most stress-tolerant tardigrade species. Precise gene repertoire analyses reveal the presence of a small proportion (1.2% or less) of putative foreign genes, loss of gene pathways that promote stress damage, expansion of gene families related to ameliorating damage, and evolution and high expression of novel tardigrade-unique proteins. Minor changes in the gene expression profiles during dehydration and rehydration suggest constitutive expression of tolerance-related genes. Using human cultured cells, we demonstrate that a tardigrade-unique DNA-associating protein suppresses X-ray-induced DNA damage by ~40% and improves radiotolerance. These findings indicate the relevance of tardigrade-unique proteins to tolerability and tardigrades could be a bountiful source of new protection genes and mechanisms.

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Sep 23, 2016   Fetal Timeline   Maternal Timeline   News   News Archive   

A scanning electron microscope image of the incredible tardigrade.
Image Credit: Tanaka S, Sagara H, Kunieda



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