Ice crystallization and freeze tolerance in embryonic stages of the tardigrade Milnesium tardigradum.

In tardigrades, tolerance to low temperature is well known and allows them to cope with subzero temperatures in their environment. Although the ability to tolerate freezing body water has been demonstrated in some tardigrades, freeze tolerance of embryonic stages has been little studied, although this has ecological significance. In this study, we evaluated the subzero temperature survival of five different developmental stages of the eutardigrade species Milnesium tardigradum after freezing to -30 degrees C.

Stress response in tardigrades: differential gene expression of molecular chaperones.

Semi-terrestrial tardigrades exhibit a remarkable tolerance to desiccation by entering a state called anhydrobiosis. In this state, they show a strong resistance against several kinds of physical extremes. Because of the probable importance of stress proteins during the phases of dehydration and rehydration, the relative abundance of transcripts coding for two alpha-crystallin heat-shock proteins (Mt-sHsp17.

High-temperature tolerance in anhydrobiotic tardigrades is limited by glass transition.

Survival in microhabitats that experience extreme fluctuations in water availability and temperature requires special adaptations. To withstand such environmental conditions, tardigrades, as well as some nematodes and rotifers, enter a completely desiccated state known as anhydrobiosis. We examined the effects of high temperatures on fully desiccated (anhydrobiotic) tardigrades.

DNA damage in storage cells of anhydrobiotic tardigrades.

In order to recover without any apparent damage, tardigrades have evolved effective adaptations to preserve the integrity of cells and tissues in the anhydrobiotic state. Despite those adaptations and the fact that the process of biological ageing comes to a stop during anhydrobiosis, the time animals can persist in this state is limited; after exceedingly long anhydrobiotic periods tardigrades fail to recover. Using the single cell gel electrophoresis (comet assay) technique to study the effect of anhydrobiosis on the integrity of deoxyribonucleic acid, we showed that the DNA in storage cells of the tardigrade Milnesium tardigradum was well protected during transition from the active into the anhydrobiotic state.

Freeze tolerance, supercooling points and ice formation: comparative studies on the subzero temperature survival of limno-terrestrial tardigrades.

Many limno-terrestrial tardigrades live in unstable habitats where they experience extreme environmental conditions such as drought, heat and subzero temperatures. Although their stress tolerance is often related only to the anhydrobiotic state, tardigrades can also be exposed to great daily temperature fluctuations without dehydration. Survival of subzero temperatures in an active state requires either the ability to tolerate the freezing of body water or mechanisms to decrease the freezing point.