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08 November 2016

Tardigrades, Tiny Animals with Superpowers

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The toughest animal on the planet is microscopic. Only measuring half a millimeter in length, they can be found everywhere, since they live in the water layer of mosses and lichens that encircles the globe. We’re talking about the tardigrade, also known as the ‘water bear’ for its particular gait similar to those powerful mammals. The tardigrade is one of the most fascinating micro-animals on the planet and each time that something new is discovered about its genome it appears in the most prestigious scientific publications. What qualities does this tiny animal possess that attract so much attention from the scientific community?

Tardigrade, with moss of 1 milimeter, analysed under the microscope. Credit: Eye of Science/Science Source Images

Superpowers. The tardigrade has a unique gene that protects it from harmful radiation, it can survive more than 10 years without water, it can endure extreme temperatures ranging from more than 100 degrees Celsius down to 196 degrees below zero, it can withstand pressures of 6,000 atmospheres and can also tolerate being in outer space. This last ability was discovered in 2007, when the European Space Agency and Russia sent the FOTON-M3 probe into space with a group of tardigrades aboard, and the creatures not only didn’t die, but they kept their reproductive capacity intact. Ever since then, they have been recognized as the most resilient animal on the planet.

Surviving 30 years frozen

This year, scientists at the National Institute of Polar Research of Japan (NIPR) found that a tardigrade had survived after being frozen for more than 30 years at the South Pole. The finding, in addition to increasing the excitement about this creature, could have future implications for humans. To be able to survive being frozen, tardigrades enter a state of suspended animation known as cryptobiosis, a process that reduces or stops all metabolic processes until the conditions return to normal.

This is a natural strategy of tardigrades that shares the essence of the dream of Walt Disney. The most famous creator of animation in history was interested in cryonics (an interest that led to the false legend that his body was frozen), which is the preservation at low temperatures of bodies that modern medicine can no longer keep alive, with the intention of treating and reviving them in the future. Researchers from the NIPR of Japan believe that the study of tardigrades will help us learn more about this type of cryptobiotic process.

All these discoveries contribute to the admiration of this enigmatic creature and reinforce the big question: how do they stay alive? Seeking rational explanations for these “superpowers”, many universities have launched studies on this creature. This treasure hunt has even led to studies with hypotheses that contradict each other. In 2015, researchers at the University of North Carolina sequenced the genome of a tardigrade for the first time and believed they had found evidence of its ability to transmit genes horizontally, i.e. to acquire foreign genes from other species. Months later, they had to retract their study after discovering that bacterial contamination of the samples had likely occurred.

A gene shield against X-rays

In September 2016, at the height of the quest to solve the mystery of the ‘water bears’, the prestigious scientific journal Nature Communications published a study by the University of Tokyo that aims to shed some light on this micro-animal. The research team, led by Takekazu Kunieda, discovered in the Ramazzottius variornatus (one of the hardier species of ‘water bear’) a single gene that could be the one conferring greater resilience to this species.

Image of a tardigradre in active state. Credit: Tanaka S, Sagara H, Kunieda.

The gene produces Dsup –short for “damage suppressor”– a protective protein that binds together and envelops the DNA of the tardigrade like a blanket to avoid damage to cells. Researchers have found that this protein acts as a shield against X-ray radiation. In addition, applying it to human cells grown in the laboratory, they found that they received up to 40% less radiation damage.

Now, researchers want to artificially construct human cells that can produce Dsup. The goal is to apply the genome sequencing of the most resilient animal in the world in the search for cures or solutions for human beings. This latest discovery could partly protect the cells of cancer patients who are undergoing radiation treatment. It’s just one example of how much remains for us to learn about a micro-animal that after being frozen at –80°C for 10 years, only needs 20 minutes after thawing to start walking again, a creature that since it appeared on Earth about 500 million years ago, has survived five mass extinctions.

Beatriz Guillén for Ventana al Conocimiento

@BeaGTorres

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