Thermotolerance and heat shock response in the cold-stenothermal chironomid (NE Italy)

Abstract

To better understand the physiological capability of cold-stenothermal organisms to survive high-temperature stress, we analyzed the thermotolerance limits and the expression level of hsp70 genes under temperature stress in the alpine midge Pseudodiamesa branickii (Diptera Chironomidae). A lethal temperature (LT(100)) of 36°C and a lethal temperature 50% (LT(50)) of 32.2°C were found for the cold-stenothermal larvae after short-term shocks (1 h). Additional experiments revealed that the duration of the exposure negatively influenced survival, whereas a prior exposure to a less severe high temperature generated an increase in survival. To investigate the molecular basis of this high thermotolerance, the expression of the hsp70 gene family was surveyed via semi-quantitative reverse transcription-polymerase chain reaction analysis in treated larvae. The constitutive (hsc70) and inducible (hsp70) forms were both analyzed. Larvae of P. branickii showed a significant up-regulation of inducible hsp70 gene with increasing temperatures and an over-expression of both hsp70 and hsc70 by increasing the time of exposure. Different from that was shown in many cold-stenothermal Antarctic organisms, P. branickii was able to activate hsp70 genes transcription (equal to heat shock response) in response to thermal stress. Finally, the unclear relationship between hsp70 expression and survival led us to surmise that genes other than hsp70 and other processes apart from the biochemical processes might generate the high thermaltolerance of P. branickii larvae. These results and future high-throughput studies at both the transcriptome and proteome level will improve our ability to predict the future geographic distribution of this species within the context of global warming.

ADrosophilaheat shock response represents an exception rather than a rule amongst Diptera species

“…Quite a different type of HSR was observed in other Chironomidae species. The transcription of hsp70 was investigated in the larvae of another Diamesinae representative, Pseudodiamesa branickii (Nowicki, 1873) (Bernab o et al, 2011) and in two members of the subfamily Chironominae, Chironomus tentans Fabricius, 1805 and Chironomus yoshimatsui Martin et Sublette, 1972 (Yoshimi et al, 2009). All of these species displayed a low hsp70 mRNA level at normal temperatures that was strongly induced by HS and a pattern of hsp70 mRNA synthesis that resembles the pattern observed in Stratiomyidae and Drosophila.…”

Thermal survival limits of young and mature larvae of a cold stenothermal chironomid from the Alps (Diamesinae: Pseudodiamesa branickii [Nowicki, 1873])

“…Young (1st and 2nd instar) and mature (3rd and 4th instar) larvae of the cold‐stenothermal Diamesinae P. branickii were used in this study. Our previous studies on this species highlighted that mature larvae are thermotolerant (LT 50 = 32.2 °C, LT 100 = 36 °C) (Bernabò et al ., ) and moderately freezing tolerant (SCP = ‐6.37 ± 0.23 °C, LLT 50 = ‐9.14 ± 1.21 °C, LLT 100 = ‐16.20 °C) (Lencioni et al ., ), with an oxyregulatory behavior (critical limit pressure = 33.6% sat. ; initial decrease of oxygen saturation = 41.9%; slope ratio in piecewise linear regression = 2.8, respiration at 25% saturation = 42.7%) (Lencioni et al ., ).…”

The Co-induced Effects of Molybdenum and Cadmium on Antioxidants and Heat Shock Proteins in Duck Kidneys

“…the synthesis of most proteins is retarded, but a group of highly conserved proteins known as heat shock proteins (HSPs) are rapidly synthesized [15]. As molecular chaperones, HSPs perform important functions in the folding/unfolding and translocation of proteins as well as in the assembly/disassembly of protein complexes [16]. Ivanina et al reported HSP60 and HSP70 protein levels increased significantly in Cd-exposed gill cells [17].…”