Freezing of body fluids induces metallothionein gene expression in earthworms (Dendrobaena octaedra).
The molecular mechanisms activated by environmental contaminants and natural stressors such as freezing need to be investigated in order to better understand the mechanisms of interaction and potential effects that combined stressors may have on organisms. Using the freeze-tolerant earthworm Dendrobaena octaedra as model species, we exposed worms to freezing and exposure to sublethal copper in a factorial design and investigated the transcription of candidate genes for metal and cold stress. We hypothesised that both freezing and copper would induce transcription of genes coding for heat shock proteins (hsp10 and hsp70), metallothioneins (mt1 and mt2), and glutathione-S-transferase (gst), and that the combined effects of these two stressors would be additive. The gene transcripts hsp10, hsp70, and gst were significantly upregulated by freezing, but only hsp10 was upregulated by copper. We found that copper at the time of sampling had no effect on transcription of two metallothionein genes whereas transcription was strongly upregulated by freezing. Moreover, there was a significant interaction causing more than additive transcription rates of mt1 in the copper/freezing treatment suggesting that freeze-induced cellular dehydration increases the concentration of free copper ions in the cytosol. This metallothionein response to freezing is likely adaptive and possibly provides protection against freeze-induced elevated metal concentrations in the cytosol and excess ROS levels due to hypoxia during freezing.
Section of Soil Fauna Ecology and Ecotoxicology, Department of Bioscience, Aarhus University, Vejlsøvej 25, DK-8600 Silkeborg, Denmark.
Karina Vincents
KV
Fisker
Section of Soil Fauna Ecology and Ecotoxicology, Department of Bioscience, Aarhus University, Vejlsøvej 25, DK-8600 Silkeborg, Denmark. Electronic address: martin.holmstrup@bios.au.dk.
Martin
M
Holmstrup
Section of Genetics, Ecology and Evolution, Department of Bioscience, Aarhus University, Ny Munkegade 116, DK-8000 Aarhus C, Denmark.
Jesper Givskov
JG
Sørensen
D000818:Animals; D001826:Body Fluids / Q000378:metabolism*; D005615:Freezing; D005786:Gene Expression Regulation; D008668:Metallothionein / Q000096:biosynthesis* / Q000235:genetics*; D009835:Oligochaeta / Q000235:genetics* / Q000378:metabolism*
D008668:Metallothionein
Freeze tolerance; Metal toxicity; Metallothionein; Oxidative stress; qPCR