Tardigrades are small metazoans resembling microscopic bears ("water-bears", 0.05 mm to 1.5 mm in size) and live in marine, freshwater and terrestrial environments, especially in lichens and mosses [1
]. They are a phylum of multi-cellular animals capable of reversible suspension of their metabolism and entering a state of cryptobiosis [4
]. A dehydrated tardigrade, known as anhydrobiotic tun-stage [6
], can survive for years without water. Moreover, the tun is resistant to extreme pressures and temperatures (low/high), as well as radiation and vaccuum [8
Well known species include Hypsibius dujardini
which is an obligatory parthenogenetic species [14
]. The tardigrade H. dujardini
can be cultured continuously for decades and can be cryopreserved. It has a compact genome, a little smaller than that of Caenorhabditis elegans
or Drosophila melanogaster
, and the rate of protein evolution in H. dujardini
is similar to that of other metazoan taxa [15
]. H. dujardini
has a short generation time, 13-14 days at room temperature. Embryos of H. dujardini
have a stereotyped cleavage pattern with asymmetric cell divisions, nuclear migrations, and cell migrations occurring in reproducible patterns [15
]. Molecular data are sparse but include the purinergic receptor occuring in H. dujardini
is an abundant and ubiquitous terrestrial tardigrade species in Europe and possibly worldwide [17
]. It has unique anatomy and motion characteristics compared to other water bears. Most water bears prefer vegetarian food, M. tardigradum
is more carnivorous, feeding on rotifers and nematodes. The animals are really tough and long-living, one of the reasons why M. tardigradum
is one of the best-studied species so far.
Questions of general interest are: How related are tardigrade proteins to each other? Which protein families provide tardigrade-specific adaptations? Which regulatory elements influence the mRNA stability? Starting from all published tardigrade sequences as well as 607 unpublished new sequences from Milnesium tardigradum
, we analyse tardigrade specific clusters of related proteins, functional protein clusters and conserved regulatory elements in mRNA mainly involved in mRNA stability. The different clusters and identified motifs are analysed and discussed, all data are also available as a first anchor to study specific adaptations of tardigrades in more detail (Tardigrade workbench). Furthermore, the tardigrade analyzer, a sequence server to analyse individual tardigrade specific sequences, is made available. It will be regularly updated to include new tardigrade sequences. It has a number of new features for tardigrade analysis not available from standard servers such as the NIH Entrez system [18
]: several new species-specific searches (Echiniscus testudo
, Tulinus stephaniae
), additional new sequence information (M. tardigradum
) and pattern-searches for nucleotide sequences (including pattern search on non-redundant protein database, NRDB). An easy search for clusters of orthologous groups (COG, [19
]) different from the COGnitor tool [20
] allowing tardigrade specific COG and eukaryotic COG (KOG) searches is also available.
Furthermore, a batch mode allows a rapid analysis of up to 100 sequences simultaneously when uploaded in a file in FASTA format (for tardigrade species or NRDB).
Two fifths of the tardigrade sequences cluster in longer protein families, and we hypothesise for a number of these that they are implicated in the unique stress adaptation potential of tardigrades. We find also ten tardigrade specific clusters. The unique tardigrade adaptions are furthermore indicated by a number of functional COGs and KOGs identified here, showing a particular emphasis on the protection of proteins and DNA. RNA read out is specifically regulated by several motifs for mRNA stability clearly overrepresented in tardigrades.