Discovery explains how tardigrades survive without water

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"Scientists studying the biology of the tardigrade have filled in important new details around how the tiny aquatic creature can survive the harshest of conditions. The discovery centers on a newfound mechanism that kicks into gear as dehydration sets in, protecting cells from death due to mechanical stress. ...
The team was investigating cytoplasmic-abundant heat soluble (CAHS) proteins, which recent research has shown become activated in tardigrades when dehydration sets in.
In exploring their role further, the team found that in dehydrated tardigrade cells, the proteins come together to form gel-like networks of protective filaments that help the cells keep their shape as their water content dries up. When the tardigrade cells were rehydrated the process is reversed ..."

"Some species of tardigrades, or water bears as the tiny aquatic creatures are also known, can survive in different environments often hostile or even fatal to most forms of life. For the first time, researchers describe a new mechanism that explains how some tardigrades can endure extreme dehydration without dying. They explored proteins that form a gel during cellular dehydration. This gel stiffens to support and protect the cells from mechanical stress that would otherwise kill them. These proteins have also been shown to work in insect cells and even show limited functionality in human cultured cells. ..."

From the abstract:

"Tardigrades are able to tolerate almost complete dehydration by entering a reversible ametabolic state called anhydrobiosis and resume their animation upon rehydration. Dehydrated tardigrades are exceptionally stable and withstand various physical extremes. Although trehalose and late embryogenesis abundant (LEA) proteins have been extensively studied as potent protectants against dehydration in other anhydrobiotic organisms, tardigrades produce high amounts of tardigrade-unique protective proteins. Cytoplasmic-abundant heat-soluble (CAHS) proteins are uniquely invented in the lineage of eutardigrades, a major class of the phylum Tardigrada and are essential for their anhydrobiotic survival. ... ... Unexpectedly, we rediscovered CAHS proteins as highly enriched in T-DRYPs, 3 of which were major components of T-DRYPs. We revealed that these CAHS proteins reversibly polymerize into many cytoskeleton-like filaments depending on hyperosmotic stress in cultured cells and undergo reversible gel-transition in vitro. Furthermore, CAHS proteins increased cell stiffness in a hyperosmotic stress-dependent manner and counteract the cell shrinkage caused by osmotic pressure, and even improved the survival against hyperosmotic stress. The conserved putative helical C-terminal region is necessary and sufficient for filament formation by CAHS proteins, and mutations disrupting the secondary structure of this region impaired both the filament formation and the gel transition. On the basis of these results, we propose that CAHS proteins are novel cytoskeleton-like proteins that form filamentous networks and undergo gel-transition in a stress-dependent manner to provide on-demand physical stabilization of cell integrity against deformative forces during dehydration and could contribute to the exceptional physical stability in a dehydrated state."

Discovery explains how unkillable tardigrades survive without water

How tardigrades bear dehydration A new mechanism explains how water bears survive in some extreme conditions

Stress-dependent cell stiffening by tardigrade tolerance proteins that reversibly form a filamentous network and gel (open access)