These genes protect resilient water bears from radiation

Tardigrades, fondly referred to as water bears, are seemingly indestructible. Go ahead and raise these microscopic animals in the freezing cold of Antarctica or worse, not a problem. Toss a few in the dead vacuum of outer space, no sweat. And a new peek into the toughest versions of these gritty creatures may explain why.

When Ramazzottius varieornatus tardigrades encounter dryness, their body water content drops to 2.5 percent, their bodies shrivel and they show no signs of life. Add back a drop of water (pictured), and they resume their activity. Photo by Daiki D. Horikawa

Researchers in Japan have sequenced the genome of Ramazzottius varieornatus tardigrades, the most stress-tolerant species on the planet, to unlock the genetic secrets behind its ability to survive. The investigation, led by University of Tokyo biologist Takekazu Kunieda, focused on genes that may explain the tardigrade’s main survival tactic: dehydration.

All tardigrades rely on swimming in water to reproduce and grow, but then can also survive almost complete dehydration. Kunieda’s team found R. varieornatus possess extra copies of stress-related genes required to survive this extreme state.

One example involves superoxide dismutases (SODs), a family of genes that fight oxidative stress. The researchers found 16 different SODs in their tardigrade, while most animals possess only 10. A similar trend applied to the DNA repair gene MRE11, which can protect stress or radiation-related mutations. The water bears had four copies, while other animals typically have one.

Another gene — Dsup — protected this water bear from extreme ultraviolet radiation, and the scientists were able to transfer this train into human cells growing in a petri dish. It’s way too soon to claim that similar protection could be passed into whole humans or other animals. But the research, published today in Nature Communications, offers clues into the limits of what is possible for cells and stress tolerance.