Stress gene (hsp70) sequences and quantitative expression inMilnesium tardigradum(Tardigrada) during active and cryptobiotic stages

Abstract

SUMMARY The eutardigrade Milnesium tardigradum can undergo cryptobiosis,i.e. entry into a reversible ametabolic stage induced by dehydration, cooling and, probably, osmotic and anoxic stress. For the first time in tardigrades,we described partial sequences of three heat-shock protein (hsp70family) genes and examined gene expression on the way from an active to a cryptobiotic and back to an active stage again. Results showed different patterns of gene expression in the hsp70 isoforms. All three isoforms seem to be true heat-shock proteins since transcription could be clearly enhanced by temperature elevation. Isoform 1 and, at a lower level, isoform 3 do not seem to have a specific function for cryptobiosis. By contrast,transcription of isoform 2 is significantly induced in the transitional stage between the active and the cryptobiotic stage, resulting in a comparatively high mRNA copy number also during cryptobiosis. This pattern of induction implies that isoform 2 is the most relevant hsp70 gene for M. tardigradum individuals entering the cryptobiotic stage.

Stress response in tardigrades: differential gene expression of molecular chaperones

“…Schill et al (2004) described three isoforms of inducible hsp70 from M. tardigradum. The isoform 1 and the isoform 3 did not have a specific function for cryptobiosis.…”

“…Those molecules are able to form biological glasses, which may protect cellular structures according to the vitrification hypothesis (Crowe 2002;Crowe et al 1998). Another important factor might be the presence of late-embryogenesis abundant proteins, which have been detected in M. tardigradum (Schill et al 2004McGee et al 2005;Schokraie et al, submitted) and which are present in many organisms that survive desiccation (e.g. Wise and Tunnacliffe 2004;Goyal et al 2005;Chakrabortee et al 2007).…”

“…An additional group of animals was analysed, in which the animals were exposed to thermal stress for 1 h at 37°C in a heating block (Thermomixer 5436, Eppendorf, Hamburg, Germany). The transition stages were defined as described earlier by Schill et al (2004) as transitional stage I, in which animals had started tun formation by contracting their legs, and transitional stage II, in which animals showed distinct movements and had stretched their legs. To achieve desiccation, they were put in open microlitre tubes (Sarstedt, Nümbrecht, Germany) and into small plastic chambers with 85% relative humidity (RH) for 2 days.…”

“…Due to the remarkable ability of tardigrades to survive extreme desiccation, few studies on stress proteins (Schill et al 2004;Jönsson and Schill 2007) have been carried out to investigate the molecular mechanisms of anhydrobiosis. One isoform of a heat-inducible heat-shock protein (Hsp70) has been described by Schill et al (2004) as upregulated in the transition phase from the active to the anhydrobiotic state in Milnesium tardigradum.…”

“…One isoform of a heat-inducible heat-shock protein (Hsp70) has been described by Schill et al (2004) as upregulated in the transition phase from the active to the anhydrobiotic state in Milnesium tardigradum.…”