Mechanisms and molecular adaptation to extreme dehydration in tardigrades: Hsp gene expression in Milnesium tardigradum

Abstract

The tardigrade Milnesium tardigradum Doyere 1840 is a well-known cosmopolitan species and a typical inhabitant of moist environments which facilitate the animal's gaseous exchange and avoid desiccation. However, such habitats frequently undergo seasonal changes that impact animal life. M. tardigradum is able to survive these periods of adverse conditions due to its ability to enter into a anhydrobiotic state. In adverse environments, all terrestrial and freshwater tardigades arrest their metabolic activity and get dehydrated to form the tun state. In the anhydrobiotic stage, tardigrades showextraordinary tolerance tophysical extremes includinghigh-energy radiation, immersion inorganic solvents, brief exposure to high temperatures and prolonged exposure to indefinitely low temperatures. When environmental conditions are adequate, tuns rehydrate and the animals resume metabolic activity. Drying of cells generally leads to massive damage to cellular membranes and proteins, which eventually results in cell death and, consequently, in the death of the entire organism.Heat shock proteins and theirmolecular partners are known to play diverse roles, even in unstressed cells, in successful folding, assembly, intracellular localization, secretion, regulation, and degradation of other proteins. In this study, a complementary focus is on tardigrades undergoing stress in nature and on the roles of stress genes of the hsp10, hsp20/30, hsp40, hsp60, hsp70 and hsp90 family in the stress physiology ofwhole organisms in different life history stages. This study is part of the project www.FUNCRYPTA.de, funded by the German Federal Ministry of Education and Research, BMBF (0313838).