There is no animal on Earth more hardy than the tiny tardigrade. It can withstand freezing at -272°C, the vacuum of outer space, and even exposure to X-rays 500 times more than would kill a human.
In other words, the creature can withstand conditions that do not even exist on Earth. This otherworldly resilience, combined with their attractive appearance, has made tardigrades favorites among animal lovers. But beyond that, researchers are looking at microscopic animals, about the size of a dust mite, to learn how to prepare humans and crops to deal with the rigors of space travel.
The tardigrade’s indestructibility is due to its adaptation to its environment—which may seem surprising since it lives in seemingly cozy places, like the cool, damp clumps of moss that dot a garden wall. As a sign of respect for such habitats, as well as a plump appearance, some people call the tardigrade water bears or, cutely, moss pigs.
But it turned out that the damp, moss-covered home of a tardigrade can dry out many times a year. Desiccation is quite catastrophic for most living things. It damages cells in about the same way as freezing, vacuum, and radiation.
First, drying leads to high levels of peroxides and other reactive oxygen species. These toxic molecules cut the cell’s DNA into short fragments, just as radiation does. Desiccation also causes cell membranes to wrinkle and crack. And it can cause delicate proteins to unfold, rendering them as useless as crumpled paper airplanes. Pacisomes have developed special strategies to deal with these types of damage.
When the tardigrade dries up, its cells secrete several strange proteins that are unlike anything found in other animals. Proteins are soft and shapeless in water. But when the water disappears, the proteins self-assemble into long, crossed fibers that fill the interior of the cell. Like packing peanuts from Styrofoam, the fibers support cell membranes and proteins, preventing them from tearing or unfolding.
At least two species of tardigrades also produce another protein that is not found in other animals on Earth. This protein, called Dsup, short for “damage suppressor,” binds to DNA and can physically protect it from reactive oxygen species.
Mimicking tardigrades may one day help humans colonize outer space. Food crops, yeast, and insects can be engineered to produce slow-moving proteins, allowing these organisms to grow more efficiently on spacecraft, where radiation levels are higher than on Earth.
Scientists have already inserted the Dsup protein gene into human cells in the laboratory. Many of these modified cells survived exposure to X-rays or peroxides, which kill normal cells. And when inserted into tobacco plants—an experimental model for food crops—the Dsup gene seemed to protect the plants from exposure to a DNA-damaging chemical called ethyl methanesulfonate. Plants with the extra gene grew faster than those without it. Plants with Dsup also experienced less DNA damage when exposed to UV radiation.
The tadpoles’ peanut-packing proteins show early signs of protecting humans. After being modified to produce these proteins, human cells became resistant to camptothecin, a chemotherapy agent that kills cells, researchers reported in ACS Synthetic Biology March 18. The tardigrade proteins did this by suppressing apoptosis, the cell’s self-destructive program that is often triggered by exposure to harmful chemicals or radiation.
So, if humans are ever going to reach for the stars, they might be able to do so by standing on the shoulders of the tiny eight-legged endurance experts in your backyard.
