Researchers Discover Tardigrades Can Repair DNA Damaged by Gamma or X-ray Radiation.
Molecular biologist Dr. De Cian and her colleagues exposed tardigrades to gamma rays, a dose hundreds of times more intense than that needed to be lethal. However, the tardigrades survived and continued to behave as if nothing had happened. Scientists have long known that tardigrades possess radiation resistance, but it was only recently that De Cian and her team uncovered the secret behind their resilience. They found that tardigrades are masters of molecular recovery, able to quickly reassemble broken DNA strands, according to two studies published in January on eLife and on April 12 in Current Biology.
Tardigrade observed under a color scanning electron microscope. (Photo: Steve Gschmeissner/Science Photo Library).
Scientists have sought for centuries to uncover the defensive capabilities of tardigrades. In 1776, Italian naturalist Lazzaro Spallanzani described how tardigrades could completely desiccate and then revive upon rehydration. In the decades that followed, researchers found that tardigrades could withstand extreme pressures, deep freezing, and even space travel.
In 1963, a group of French researchers discovered that tardigrades can endure strong X-rays. More recent studies found that certain species of tardigrades can withstand radiation levels 1,400 times higher than those required to be lethal. Radiation is perilous because it breaks DNA chains. High-energy rays can directly damage DNA molecules and also harm other molecules within cells, which can then attack DNA.
Scientists suspected that tardigrades could prevent or eliminate this damage. In 2016, a research group at the University of Tokyo discovered a protein called Dsup that appears to protect tardigrade genes from high-energy rays and altered molecules. They tested this hypothesis by introducing Dsup into human cells and exposing them to X-rays. Cells containing Dsup were less damaged than those without the tardigrade protein.
This study piqued De Cian’s interest in tardigrades. She and her colleagues studied tardigrades collected from her garden in Paris, along with a species from England and another from Antarctica. Their findings indicated that gamma rays damaged the DNA of tardigrades but did not kill them. In another independent study, biologist Courtney Clark-Hachtel from the University of North Carolina at Asheville and her team found that tardigrades had fragmented genes.
These findings suggest that the Dsup protein itself does not prevent DNA damage, although it may offer some protection. It is challenging to ascertain definitively, as scientists are still working on conducting experiments with tardigrades. For instance, they cannot manipulate them without the Dsup gene to see how they handle radiation.
Both new studies reveal another secret about tardigrades. They can rapidly repair broken DNA. After exposure to radiation, their cells utilize hundreds of genes to produce a significant amount of new proteins. Many of these genes are familiar to biologists, as other species, including humans, use them to repair damaged DNA. Human cells constantly repair genes, with a typical human cell experiencing about 40 DNA breaks per day, and each time, the cell repairs them. Tardigrades produce repair cells in such astonishingly large numbers.
De Cian’s team found that radiation also prompts tardigrades to produce some proteins never before seen in other animals. Currently, their functions remain largely a mystery. Scientists chose TRD1, an exceptionally abundant protein, for further study. When introduced into human cells, it seems to help those cells withstand DNA damage. Concordet speculates that TRD1 might bind tightly to chromosomes and keep them in the correct shape, even as DNA strands begin to suffer damage.
Research into proteins like TRD1 not only unveils the superpowers of tardigrades but could also lead to new ideas for treating various diseases. DNA damage plays a significant role in many types of cancer.
