Tardigrades are invertebrate animals, some of which can enter into an ametabolic desiccated state called anhydrobiosis. In this state, tardigrades are extremotolerant and able to survive open space environments characterized by severe vacuum and intense radiation. For these reasons, tardigrades are expected to serve as important model organisms for astrobiological studies, particularly those focusing on how multicellular organisms can withstand the extreme environments of space and the possibility of extraterrestrial multicellular life forms. To develop tardigrades as model organisms, we established a culture system for the tardigrade species Ramazzottius varieornatus, a species that is tolerant to several types of extreme physical and chemical environmental conditions while in an anhydrobiotic, or "tun", state. Based on studies using this culture system and the extremotolerance of this tardigrade in connection with its anhydrobiotic capacity, R. varieornatus is a suitable model organism for astrobiological studies and will provide new insight into the mechanisms underlying the ability of multicellular organisms to tolerate extreme environments.

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Fine control of protein expression must be crucial for hibernators to promote energy conservation and survival during harsh winters. This study was aimed at investigating seasonal proteomic plasticity in order to evaluate physiological relevance of proteomic adjustments in the brain of the Murina leucogaster bat in three functional states: summer-active (SA), torpor (TR), and early phase of arousal (AR). Our two-dimensional electrophoresis and immunoblotting analyses revealed that 74% of identified neuronal, synaptic, metabolic, and stress proteins maintained stable levels throughout the three states. Proteins associated with axonal outgrowth and synaptic transmission (e.g., dihydropyrimidinase related protein-2 and N-ethylmaleimide sensitive fusion protein) and heme catabolism (biliverdin reductase B) were generally downregulated in TR and upregulated in AR. The levels of molecular chaperones such as heat shock protein 70 and glucose-regulated protein 78 remained unchanged over the three states. In parallel, glucose and lactate concentrations were relatively low in TR, whereas the glucose concentration was low but the lactate level was high in AR, implying metabolic stress due to arousal. These findings suggest that seasonal proteomic variability was observed mainly in proteins that functioned to regulate neural network, antioxidant activity, and neuroprotection in the hibernator brain.

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