What makes tardigrades difficult?

No monster on Earth is tougher than the little tardigrade. It can survive freezing to -272 ° Celsius, being exposed to the vacuum of space and even to explosions 500 times the dose of X -rays that would kill a person.

In other words, the creature can tolerate conditions that are not even on Earth. This unearthly stability, combined with their attractive appearance, has made tardigrades a favorite of animal lovers. But more than that, researchers are looking at microscopic animals, which are about the size of a dust mite, to learn how to prepare people and crops to handle the rigors of space travel.

The tardigrade’s indestructibility comes from its adaptations to its environment – which may seem surprising, since it lives in seemingly soft areas, such as cold and wet clusters of moss that dot the garden wall. As a tribute to such habitats, along with a slippery appearance, some people call tardigrades water bears or, adorably, moss piglets.

But it turns out that the damp and mossy home of the tardigrade can dry out several times per year. Drainage is quite catastrophic for most living things. It destroys cells in some of the same ways that freezing, vacuum and radiation do.

For one thing, dehydration leads to high levels of peroxide and other reactive oxygen species. These toxic molecules break a cell’s DNA into short fragments – just as radiation does. Dehydration also causes cell membranes to wrinkle and crack. And it can lead to delicate proteins opening up, making them useless like crumpled paper planes. Tardigrades have evolved special techniques for dealing with these types of damage.

Crisscrossing proteins shown in the dehydration of tardigrade cells
As a tardigrade dries, its cells create long, crisscrossing proteins (shown) that soften and protect the cell membranes.M. Yagi-Utsumi et al/Scientific Reports 2021

As the tardigrade dries up, its cells secrete some unique proteins unlike anything found in other animals. In water, proteins are floppy and amorphous. But as water is lost, proteins accumulate themselves in long and confined fibers that fill the inside of the cell. Like Styrofoam that packs nuts, the fibers support cell membranes and proteins, preventing them from breaking or opening.

At least two species of tardigrade also produce another protein that is not present in other animals on Earth. This protein, called Dsup, which is short for “damage suppressor,” binds to DNA and can physically protect it from reactive forms of oxygen.

Simulating tardigrades can help humans cover outer space. Food crops, yeast and insects can be engineered to produce tardigrade proteins, allowing these organisms to grow more efficiently in spacecraft where radiation levels have risen compared to Earth.

Scientists have already inserted the gene for the Dsup protein into human cells in the lab. Many of those modified cells survive the level of X-ray or peroxide chemicals that kill ordinary cells (SN: 11/9/19, p. 13). And when inserted into tobacco plants – an experimental model for food crops – the gene for Dsup seems to protect plants from exposure to a DNA -damaging chemical called ethyl methanesulfonate. Plants with excess gene grow faster than those without it. Plants with Dsup also had less DNA damage when exposed to ultraviolet radiation.

Microscopic tardigrades
Microscopic tardigrades can withstand freezing cold, dryness and extreme levels of radiation thanks to unique molecular adaptations.VIDEOLOGY/ISTOCK/GETTY IMAGES PLUS

The “packing peanut” proteins of the Tardigrades are showing early signs of being protective for humans. When modified to produce proteins, human cells become resistant to camptothecin, a chemotherapy agent that kills cells, researchers reported on March 18th. ACS Synthetic Biology. Tardigrade proteins do this by inhibiting apoptosis, a cellular self-destruct program often triggered by exposure to harmful chemicals or radiation.

So if people succeed in reaching the stars, they can accomplish this task, in part, by standing on the shoulders of small endurance specialists with eight feet in your backyard. .