To introduce her children to the hidden wonders of the animal kingdom a few years ago, Anne De Cian entered her garden in Paris. Dr. De Cian, a molecular biologist, took pieces of moss, then went back inside to soak them in water and put them under the microscope. Her children looked through the eyepiece at the strange, eight-legged creature climbing over the moss.
“They were impressed,” said Dr. De Cian.
But he didn’t finish with the small animals, known as tardigrades. He brought them to his laboratory at the French National Museum of Natural History, where he and his colleagues hit them with gamma rays. The explosions are hundreds of times greater than the radiation required to kill a person. But the tardigrades survived, continuing their lives as if nothing had happened.
Scientists have known for a long time that tardigrades are extremely resistant to radiation, but only now did Dr. De Cian and other researchers the secrets of their survival. Tardigrades have become masters of molecular repair, rapidly rebuilding piles of broken DNA, according to a study published Friday and another from earlier this year.
Scientists have been trying to breach the tardigrades’ defenses for centuries. In 1776, Lazzaro Spallanzani, an Italian naturalist, described how animals could be completely dried up and then revived by a splash of water. In the decades that followed, scientists discovered that tardigrades could withstand crushing pressure, deep freezing and even a trip to space.
In 1963, a group of French researchers discovered that tardigrades could withstand massive X-ray bursts. In more recent studies, researchers have discovered that some species of tardigrades can withstand a dose of radiation 1,400 times higher than what is required to kill a human.
Radiation is deadly because it damages DNA strands. A high-energy ray that hits a DNA molecule can cause direct damage; it can also wreak havoc by bumping into another molecule within a cell. That modified molecule can attack DNA.
Scientists suspect that tardigrades can prevent or reverse this damage. In 2016, researchers at the University of Tokyo discovered a protein called Dsup, which appears to protect tardigrade genes from energy beams and errant molecules. The researchers tested their hypothesis by putting Dsup in human cells and exposing them to X-rays. Dsup cells were less damaged than cells lacking the tardigrade protein.
That research piqued the interest of Dr. De Cian on tardigrades. He and his colleagues studied the animals he collected in his garden in Paris, including one species found in England and a third from Antarctica. As they reported in January, gamma rays damaged the tardigrades’ DNA, but failed to kill them.
Courtney Clark-Hachtel, a biologist at the University of North Carolina at Asheville, and her colleagues independently found that tardigrades ended up with broken genes. Their study was published Friday in the journal Current Biology.
These findings suggest that Dsup by itself does not prevent DNA damage, although it is possible that the proteins provide partial protection. It’s hard to know for sure because scientists are still figuring out how to run experiments on tardigrades. They couldn’t engineer animals without the Dsup gene, for example, to see how they would handle radiation.
“We wanted to do this experiment,” said Jean-Paul Concordet, the collaborator of Dr. De Cian in the museum. “But what we can do with tardigrades is still incomplete.”
Both new studies revealed another trick of tardigrades: They quickly repair their damaged DNA.
After tardigrades are exposed to radiation, their cells use hundreds of genes to make a new batch of proteins. Many of these genes are familiar to biologists, because other species – including ourselves – use them to repair damaged DNA.
Our own cells are constantly editing genes. The strands of DNA in a typical human cell break about 40 times a day — and each time, our cells have to repair them.
Tardigrades produce these common repair proteins in astonishingly large amounts. “I thought, ‘This is ridiculous’,” Dr. Clark-Hachtel recalled when she first measured their levels.
Dr. also discovered De Cian and his colleagues found that radiation causes tardigrades to produce certain proteins not seen in other animals. For now, their functions remain mostly a mystery.
The scientists chose a particularly abundant protein to study, called TRD1. When inserted into human cells, it seems to help the cells withstand damage to their DNA. Dr. assumed Concordet that TRD1 can pick up chromosomes and hold them in their proper shape, even as their strands begin to unravel.
Studying proteins like TRD1 will not only reveal the powers of tardigrades, said Dr. Concordet, but could also lead to new ideas on how to treat medical ailments. DNA damage plays a part in many types of cancer, for example. “Any tricks they use we can benefit from,” said Dr. Concordet.
Dr. still sees Concordet that it is strange that tardigrades are so good at surviving radiation. After all, they don’t have to live in nuclear power plants or uranium-lined caves.
“This is one of the big enigmas: Why are these organisms resistant to radiation in the first place?” he said.
said Dr. Concordet that this tardigrade superpower might just be a rare coincidence. Dehydration can also damage DNA, so tardigrades can use their shields and repair proteins to withstand desiccation.
Although a garden in Paris may seem like an easy place to live, Dr. Concordet that this can pose many challenges to a tardigrade. Even the disappearance of the fog every morning can be a disaster.
“We don’t know what life is in that moss,” he said.
