Secrets of the water bear

Hypsibius dujardini, a type of tardigrade, imaged with scanning electron microscopy. Image credit: Willow Gabriel, Goldstein Lab via Wikimedia, CC BY-SA 2.5

Tardigrades (also known as water bears or moss piglets) are among the most resilient animals on the planet. They are termed “extremotolerant”, as while they are not true extremophiles – organisms, usually unicellular, which are adapted to thrive in extreme conditions – these incredible micro-animals are found in the most intense conditions our planet has to offer. Extremes in radiation, temperature, pressure – even the vacuum of space – all are survivable to a water bear. The question is, how? 

Tardigrades have been found all over the world, from deep sea hot springs to sheets of solid ice, but can also be found in as mundane an environment as a simple patch of moss on a wall. The key is moisture: tardigrades require a surrounding of water in order to uptake oxygen and metabolise (undergo life-sustaining chemical reactions). The real super-power of the tardigrade is their ability to continually undergo, and return from, cryptobiosis. This is a state in which the tardigrade can lose almost 99% of the water within its body, and becomes metabolically inactive. The remarkable ability of the tardigrade to remain in this state for many years, only to later rehydrate and return to life as normal, is a fascinating one.

Image credit: Kruthika Sundaram

So how do they do it? How can these tiny, miraculous animals survive, even in their dehydrated state? The answer lies in their DNA – or, rather, around it. 

Recent studies have discovered a tardigrade-unique protein called Dsup (damage suppressor). A computational experiment by the Centre of Plant Biotechnology and Genomics in Madrid revealed that the Dsup protein is one that is intrinsically disordered, and works, amazingly, by adjusting its structure to fit around the DNA that it protects. By means of strong electrostatic attractions and an incredibly high rate of flexibility, the protein physically forms an aggregate around the DNA, protecting it from harm. This is the secret to the tardigrade’s superpowers: some of the proteins from which they derive their ability to revive themselves after dehydration are found in other organisms, but Dsup is unique to the Tardigrada. 

Dsup binds to chromatin, a protein-DNA complex found in eukaryotes that packages DNA into its recognisable chromosome form. A study from the University of California examined how Dsup physically blocks radicals from disrupting cellular DNA by forming a high-energy cloud around the chromatin envelope. 

What does this mean for us? Researchers have found that Dsup is also able to make human cells resistant to X-ray radiation, which opens up innumerable pathways in pharmaceutical developments. Current work is also underway in the engineering of stress tolerant crops. While more understanding is needed before any further experimentation or thoughts of modifications emerge, the potential applications of a protein capable of protecting DNA at a cellular level are immense and seemingly limitless, ranging from cancer treatments to space travel. There is so much to learn from these tiny, unassuming creatures. The only question is, what next?

Written by Heather Jones and edited by Ailie McWhinnie.

Heather’s thoughts… Did you know that there are tardigrades on the moon? 

During the 2007 European Space Agency (ESA) Foton-M3 mission, it was discovered that tardigrades were able to withstand the extreme conditions of space travel and exposure to the sub-zero temperatures, complete oxygen-deprivation, and unrelenting solar winds of the vacuum of space. Then, in 2019, tun-state tardigrades were on-board an Israeli spacecraft when it crash-landed into the moon. Given their extreme resilience and the fact they were already in suspended animation, it is extremely likely that they are still alive! 

Heather is a second-year biological sciences student. Find her on Facebook @Heather Jones and LinkedIn @Heather Jones

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