These creatures are practically immortal and can survive in conditions where any other organism would have long perished. Recent studies have revealed the secret of their remarkable resistance to ionizing radiation.
Tardigrades, or water bears, are tiny eight-legged creatures that inhabit small bodies of water around the world. They are known for their unique abilities to survive in extreme conditions. These organisms can exist in the vacuum of space, withstand temperatures close to absolute zero and heat up to 100°C, as well as cope with pressures six times greater than the pressure at the bottom of the Mariana Trench, as well as with dehydration and freezing for many years.
Moreover, tardigrades are capable of withstanding enormous doses of radiation that would be lethal to most other forms of life on Earth. Now scientists have figured out how they manage to do this. The main reason is a unique protective protein that forms in these creatures and helps protect their DNA from radiation damage. The protein, named Dsup, apparently interacts with DNA, physically shielding it from harm while not disrupting the normal functioning of the genetic structure.
Scientists discovered Dsup during the genome sequencing of Ramazzottius varieornatus, one of the most stress-resistant species of tardigrades. To their surprise, this protein also protected human kidney cells from radiation damage when the cells were genetically modified to produce Dsup. Human cells synthesizing this protein showed a reduction in DNA damage caused by X-rays of about 40-50% compared to control cells.
However, the presence of Dsup in an animal does not guarantee its survival, as some vital cells and organs may be lost despite good protection. By studying the genome of tardigrades, scientists also found that these creatures have additional copies of other protective genes. They have 16 copies of enzymes that neutralize reactive oxygen species, while most other organisms have only 10, and four copies of MRE11 genes responsible for DNA repair, instead of the single copy typically found in animal cells.
A 2015 study showed that tardigrades have extracted up to one-sixth of their DNA from bacteria and other organisms through a process known as horizontal gene transfer. While it was unclear how exactly they did this, it is known that their DNA breaks down into small fragments when dehydrated, and the nucleus 'opens' upon rehydration, which may allow foreign DNA to enter and then mix with the animal's own genes.
