Water is a key ingredient to all life on Earth, but Tardigrades with their nigh-immortal powers can somehow handle being sapped of almost all of their H2O.
Now researchers have discovered another trick these chubby microscopic abnormalities use to survive years of extreme dehydration.
“Although water is essential for all life we know of, some tardigrades can live without it potentially for decades,” says University of Tokyo biologist Takekazu Kunieda.
Known colloquially as water bears, many of the 1,300 known species of tardigrades tolerate conditions that would be fatal to all other known life forms.
Starve them, boil them, freeze them, irradiate them, or shoot them with a gun and these distant relatives of velvet worms will come back time after time for more.
When these aquatic animals find themselves in an environment that leaches their water, the tardigrades shrivel up into a round shape called a ton.
As Kunieda, fellow University of Tokyo biologist Akihiro Tanaka, and colleagues explain in their paper, dehydrated tardigrades are exceptionally stable and can withstand many extremes, including exposure to the vacuum of space, while managing to resuscitate.
“It is thought that when water leaves a cell, some kind of protein must help the cell maintain its physical strength to avoid collapsing in on itself,” says Kunieda.
So the researchers combed through a group of tardigrades known for their dehydrating abilities called eutardigrades for proteins that could explain this phenomenon, finding 336 unique suspects.
“After testing several different types, we found that cytoplasmic abundant heat-soluble proteins (CAHS), unique to tardigrades, are responsible for protecting their cells from dehydration,” says Kunieda.
Using experiments on human and insect cells, the researchers were able to demonstrate that CAHS proteins increase cellular rigidity, strengthening the cell against shrinkage caused by loss of water pressure. The proteins even protected the cells against too much water pressure.
“Trying to see how CAHS proteins behaved in insect and human cells presented some interesting challenges,” says Tanaka.
“The typical staining method requires solutions containing water, which obviously confounds any experiment where water concentration is a factor one seeks to control. So we turned to a methanol-based solution to work around this problem.”
This allowed them to see the CAHS proteins in action in cells grown in the lab.
CAHS proteins appear to act as cellular scaffolding structures akin to the cell’s own cytoskeleton – but only when cells face the stress of water loss.
As seen in the video above, in dehydrated cells, CAHS proteins bind together to form cobwebs of supporting filaments, providing an on-demand transition to this filament-filled gel-like phase.
The cytoskeleton-like structures protect the cell from complete distortion due to lack of water pressure and likely contribute to the barrels’ incredible stability.
Called anhydrobiosis, this process can be reversed, allowing tardigrades to pick up their lives where they left off, once again moisturizing conditions return.
Scientists have previously suspected that there is a protein-based “biglass” that keeps the cellular structures of tardigrades intact during extreme desiccation.
But past studies have only looked for the genetic components of this ability; this new study looked for the actual proteins.
Clever biological tricks like these have allowed these eight-legged, but still lovable animals to reach every corner of our planet – from scorching volcanic vents and crushing pressure from the depths of our oceans to rainforests and frozen tundra.
“Everything about tardigrades is fascinating,” says Kunieda.
“The extreme range of environments in which certain species can survive leads us to explore mechanisms and structures never seen before. For a biologist, this field is a goldmine.”
The other unique proteins that Tanaka and his colleagues have isolated may hold more clues to how the tardigrades manage all their impressive feats.
This research was published in PLOS Biology.
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