Since the 1960s, scientists have known that the tiny tardigrade can withstand very intense bursts of radiation, 1,000 times stronger than most other animals could withstand. According to a new article published in the magazine Current Biology, It is not that such ionizing radiation does not damage the DNA of tardigrades; rather, tardigrades can quickly repair any such damage. The findings complement those of a separate study, published in January, that also explored tardigrades’ response to radiation.
Amazing little ones
“These animals are developing an incredible response to radiation, and that seems to be a secret to their extreme survival capabilities,” said co-author Courtney Clark-Hachtel, a postdoc in Bob Goldstein’s lab at the University of North Carolina at Chapel. Hill, who has been conducting research on tardigrades for 25 years. “What we are learning about how tardigrades overcome radiation stress may lead to new ideas about how we might try to protect other animals and microorganisms from harmful radiation.”
Tardigrades are microanimals that can survive in the harshest conditions: extreme pressure, extreme temperature, radiation, dehydration, starvation, and even exposure to the vacuum of outer space. The creatures were first described by German zoologist Johann Goeze in 1773. Four years later, Lazzaro Spallanzani, an Italian biologist, named them tardigrades (“slow walkers”). This is because tardigrades tend to lumber forward, like a bear. Since they can survive almost anywhere, they are often found in many places: deep sea trenches, fresh and saltwater sediments, rainforests, Antarctica, mud volcanoes, sand dunes, beaches, lichens and mosses. (Another name for them is “mossy piglets.”)
Tardigrades in “tun state”
But there is another very strange topic; When their humid habitat dries out, tardigrades enter something known as the “tun state,” a kind of suspended animation, in which these animals can remain for up to 10 years. When water begins to flow again, the water bears absorb it to rehydrate and come back to life. They are not technically members of the Extremophile class of organisms, as they do not thrive in extreme conditions, but are resilient. They then belong to the class of extreme-tolerant organisms. But their hardiness makes tardigrades a favorite research topic for scientists.
For example, a 2017 study showed that tardigrades use a special type of disordered protein to suspend their cells in a matrix, similar to glass, that prevents damage. The researchers called this the “tardigrade-specific intrinsically disordered protein” (TDP). In other words, the cells become vitrified. The more TDP genes a tardigrade species has, the more quickly and efficiently it will transition to the tun state.
In 2021, another team of Japanese scientists questioned this “vitrification” hypothesis, citing experimental data suggesting that the 2017 findings could be attributed to protein water retention. The following year, researchers at the University of Tokyo identified the mechanism to explain how tardigrades can survive extreme dehydration: cytoplasmic abundant heat-soluble (CAHS) proteins that form a protective gel-like network of filaments to protect dry cells. . When the tardigrade rehydrates, the filaments gradually recede, ensuring that the cell is not stressed or damaged while it regains water.
Tardigrades and ionizing radiation
When it comes to resisting ionizing radiation, a 2016 study identified a DNA damage suppressor protein, called “Dsup,” that appeared to protect tardigrade genes implanted in human cells from radiation damage. However, according to Clark-Hatchel et al., it was still unclear whether this type of protective mechanism was sufficient to fully explain the ability of tardigrades to withstand extreme radiation. Other tardigrade species appear to lack Dsup proteins, but still have the same high tolerance to radiation, suggesting that there could be other factors at play.
A team of French researchers, from the French National Museum of Natural History in Paris, carried out a series of experiments in which they attacked specimens of water bears with powerful gamma rays (which would be lethal to humans). They published their results earlier this year in the journal eLife. The French team discovered that Gamma rays actually damaged tardigrades’ DNA, much like they would damage human cells. Since the tardigrades survived, this then suggested that they were able to quickly repair damaged DNA.
