Tardigrades, tiny invertebrates measuring between 0.2 and 1.2 millimeters, are found across the globe, from ocean floors to Himalayan peaks. They are known for their remarkable resilience, surviving extreme conditions including exposure to the vacuum of space and high doses of radiation. Research indicates that they can endure X-ray doses up to 1,000 times higher than lethal levels for humans.
The first discovery of tardigrades dates back to the 18th century. Biologist Lazzaro Spallanzani (1729-1799) published a study in 1776, naming them tardigrades and describing their ability to enter a state known as cryptobiosis, where they can survive complete dehydration and later 'resurrect' upon rehydration.
Cryptobiosis is characterized as a 'suspended state of life' where no signs of life are detectable. Tardigrades collected from Antarctica have been successfully revived after 30 years in this state. Notably, the time spent in cryptobiosis does not count against their normal lifespan, which averages around 60 days in controlled environments.
Recent research from the CNRS laboratory in Montpellier has revealed insights into the internal processes of tardigrades during cryptobiosis, specifically the species Hypsibius exemplaris. This species shrinks by 38% in volume and forms a protective barrier around its cells. However, a related species, Ramazzottius varieornatus, shrinks only 32% and lacks this protective structure.
Since 2016, genetic tools enabling tardigrades to withstand extreme environments have been identified through genome sequencing. These findings suggest potential revolutionary biomedical applications, including the preservation of medications and vaccines in dehydrated forms.
Geneticists propose that these unique tardigrade genes, which are approximately 40% unknown in other species, may have been acquired through horizontal gene transfer (HGT). This mechanism allows organisms to gain genes from neighboring species, enhancing their survival capabilities.
Recent studies have shown that tardigrades have likely accumulated these unique genes over their 600 million years of existence, having survived five major extinction events. Some of these genes, such as Dsup, TDR1, and CAHS, have already been identified and demonstrate the ability to enhance resistance to lethal treatments when inserted into human or laboratory cells.
The source of these unique genes may be environmental DNA (eDNA) released by living organisms around us. Scientists have developed techniques to analyze eDNA from soil samples, allowing for the identification of species without direct observation.
As tardigrades enter cryptobiosis, their chromosomes exhibit breaks, which can be repaired upon rehydration. This process may facilitate the integration of eDNA into their genetic material, contributing to their genetic diversity.
With their capacity to absorb genes from their environment, tardigrades possess unique genetic traits that could lead to significant advancements in biomedical fields, including drug preservation and protection for astronauts during space missions.