This work provides a comparative and genetic analysis of the responses to water stress in desiccation-tolerant and desiccation-sensitive nematodes. Caenorhabditis elegans, a model organism for the study of development, aging, and cell biology was shown to be a desiccation-sensitive organism that survives relative humidities above 40\% for periods of up to seven days. Transcripts from the desiccation-tolerant species Panagrolaimus rigidus AF36 and sp. PS1579, which were expressed uniquely during separate desiccation and osmotic stresses, as well as during recovery from exposure to the dual stresses, were cloned. These sequences were used to search for similarities in the genome sequence data of C. elegans. Putative anhydrobiotic-related transcripts were identified that potentially encode heat shock protein 70, late embryogenic abundant protein, and trehalose-phosphate synthase. Other putative genes that were identified within eight separate libraries encode proteins involved in transcription (histones), protein biosynthesis (ribosomal proteins, elongation factors), protein degradation (ubiquitin, proteases), and transport and cell structure (actin, collagen). Gene ontology analysis of the cloned transcripts revealed that developmental processes are activated during exposure to the stresses as well as during recovery, which may suggest a "rejuvenation" process as a key to survival in Panagrolaimus nematodes. Genes that were up-regulated during desiccation stress in C. elegans were classified as belonging either to an early response (until 12 hours of stress), or to a late response (after 12 hours of stress). The early response was characterized by the up-regulation of a large number of genes encoding mono-oxygenases, which may suggest onset of oxidation stress during desiccation of C. elegans. The late response was characterized by the appearance of transcripts encoding proteins of the immune system, heat shock proteins (protein denaturation), and superoxide dismutases (oxidation damage). Genes in C. elegans that were down-regulated in response to desiccation stress include those encoding proteases and lysozymes (metabolic shutdown). Genes that encode channel proteins (water homeostasis) were found among the transcripts up-regulated during recovery of C. elegans. The up-regulation of gpdh-1 and hmit-1.1, two transcripts linked to hyperosmotic stress, suggest that osmotic stress is experienced by C. elegans. Comparison of these data with those obtained from exposure of C. elegans to a range of other stresses showing that the nematode C. elegans uses specific transcripts for the desiccation response; transcripts that are not induced in other stresses such as heat, anoxia or starvation. In addition, transcripts regulated during desiccation stress of C. elegans were also regulated during dauer formation, which may indicate common stress tolerant mechanisms. Recent studies in mammalian cells and C. elegans have shown that microRNAs are able to degrade and to sequester mRNA especially during stress in so called stress bodies. In this study, C. elegans microRNA knock-outs showed a significant decrease in desiccation stress survival compared to wild type C. elegans which may suggest the importance of microRNAs for stress survival in C. elegans and other organisms. / Ph. D.

To persist in extreme environments, some meiofaunal taxa have adopted outstanding resistance strategies. Recent years have seen increased enthusiasm for understanding extreme-resistance mechanisms evolved by tardigrades, nematodes and rotifers, such as the capability to tolerate complete desiccation and freezing by entering a state of reversible suspension of metabolism called anhydrobiosis and cryobiosis, respectively. In contrast, the less common phenomenon of diapause, which includes encystment and cyclomorphosis, is defined by a suspension of growth and development with a reduction in metabolic activity induced by stressful environmental conditions. Because of their unique resistance, tardigrades and rotifers have been proposed as model organisms in the fields of exobiology and space research. They are also increasingly considered in medical research with the hope that their resistance mechanisms could be used to improve the tolerance of human cells to extreme stress. This review will analyse the dormancy strategies in tardigrades, rotifers and nematodes with emphasis on mechanisms of extreme stress tolerance to identify convergent and unique strategies occurring in these distinct groups. We also examine the ecological and evolutionary consequences of extreme tolerance by summarizing recent advances in this field.

The Tardigrada are hydrophilous, segmented, molting micrometazoans that occupy a diversity of niches in freshwater, marine, and terrestrial habitats. A sister group of the arthropods, this phylum of bilaterally symmetrical lobopods, most less than 1 mm in length, have a hemocoel, a complete digestive tract, a dorsal gonad with one or two gonoducts, and a dorsal lobed brain with a ventral nerve cord and five ganglia. About 1000 species have been described based on the morphology of sclerified structures, especially the claws and buccal-pharyngeal apparatus. Reproduction occurs through fertilized or unfertilized eggs, with individuals being either gonochoric, unisexual, or hermaphroditic, and eggs are deposited either freely or within the shed exuvium. Parthenogenesis, very frequent in limnic and terrestrial tardigrades, allows them to colonize new territories by passive dispersal of a single individual. Quiescence (cryptobiosis: anhydrobiosis, anoxybiosis, cryobiosis, and osmobiosis) and diapause (encystment and resting eggs) occur during the tardigrade life history. Ecological parameters and global distribution patterns are poorly known or understood. Methods for collection, microscopy, and culturing have been developed.

This thesis is focused on the phylum Tardigrada. The main goal is to implement this topic into the curriculum of primary and secondary education. The thesis is divided in two parts - theoretical and empirical. The theoretical part comprises five basic topics: the general introduction to phylum Tardigrada and other moss fauna; extraction methods; analysis of textbooks for primary and secondary schools; and application of obtained knowledge about phylum Tardigrada in education. In this thesis, water bears are used as model organisms for creating practical suggestions for teaching methods and forms that can be used when implementing this theme into a teaching process. The empirical part presents the results of extensive study focused on the occurrence of Tardigrada in moss from variety of habitats in the Czech Republic and its implication for practical use. Keywords: moss fauna, cryptobiosis, education, teaching methods, research, analysis of textbooks

STORAGE CELLS AND THEIR ROLE IN TARDIGRADE PHYSIOLOGY Abstract Tardigrades possess remarkable tolerance to numerous stress conditions (e.g. almost complete desiccation, exposure to very low sub-zero temperature, heat stress and even exposure to space in low Earth orbit). Indeed, they are among the most radiation-resistant multi-cellular organisms. The body cavity of tardigrades is filled with the storage cells (SC). Their role in anhydrobiosis has been discussed. The main objectives of this work were to analyse (i) the occurrence of mitosis in SC, (ii) the factors constraining anhydrobiotic survival, and (iii) the general ultrastructure of SC and their ultrastructure concerning the stress conditions. Our model species, R. cf. coronifer is one of the most extensively studied tardigrades concerning anhydrobiosis. Comprehensive histochemical techniques were used in combination with SEM, TEM, and confocal microscopy. First, mitotic divisions of tardigrade SC occur with a higher frequency in juveniles than in adults and correlate with animal growth. Mitosis is more frequent in moulting tardigrades, but the overall mitotic index is low. Furthermore, tardigrades of R. cf. coronifer can survive the maximum of 6 repeated desiccation cycles with significantly declining survival rate with repeated desiccations and...

A sister group of the Arthropoda, the Tardigrada are micrometazoans that occupy a diversity of niches in freshwater, marine, and terrestrial habitats. Commonly called water bears because of their slow, lumbering gait, these molting lobopods have four pairs of legs, usually terminating in claws. Most are less than 1 mm in length, with a complete digestive tract, a dorsal gonad with one or two gonoducts, and a dorsal lobed brain with a ventral nerve cord and four bilobed ganglia, one per leg-bearing metamere. The body cavity (hemocoel) functions in respiration and circulation. Over 1200 species have been described based primarily on the morphology of the claws and buccal-pharyngeal apparatus. Individuals may be either gonochoric, unisexual, or hermaphroditic, with fertilized or unfertilized eggs deposited either freely or within the shed exuvium. Parthenogenesis occurs frequently in limnic and terrestrial tardigrades, allowing them to colonize new territories by passive dispersal of a single individual. Cryptobiosis (anhydrobiosis, anoxybiosis, cryobiosis, and osmobiosis) and diapause (encystment and resting eggs) occur during the life history. Active adults (surrounded by water) and cryptobiotic adults and eggs are primarily dispersed passively, but some active dispersal can also occur. Due to the characteristic patchy distributions of tardigrade populations, little is known about their population dynamics and trophic relationships. Improved methods for collection, microscopy, culturing, and molecular analyses have been have contributed much to our knowledge of tardigrades.