How do tardigrades survive in space?

Cute microscopic animals called tardigrades are found almost anywhere there is fresh water. They can also survive extreme conditions—even exposure to the cold vacuum of outer space—and their DNA can withstand a battering by X-ray radiation. Until now, researchers weren’t sure how they did it. Previous studies in Ramazzottius varieornatus pointed to the effects of damage suppression protein (Dsup), which protects from radiation. Now, using biochemical analysis, researchers at the University of California San Diego have discovered that Dsup binds to chromatin, the protein that wraps up DNA inside cells (eLife 2019, DOI: 10.7554/eLife.47682). Once bound, Dsup forms a protective cloud that shields the critter’s DNA from hydroxyl radicals produced by X-rays. The team found another version of the protective protein in a different tardigrade species. Although the two proteins share only about 26% of the same amino acid sequence, both protect DNA in the same way. The researchers suspect the protein clouds evolved as a survival mechanism against hydroxyl radicals in tardigrades’ natural habitats. When the environment dries up, tardigrades shift into a dormant state of dehydration, during which Dsup protection should help them survive.