title: The rapid cold hardening response of Drosophila melanogaster: complex regulation across different levels of biological organization.
abstract: Rapid cold hardening (RCH) is a form of thermal acclimation that allows ectotherms to fine-tune their physiological state to match rapid changes in thermal environment. Despite progress in recent years, there is still a considerable uncertainty regarding the physiological basis of RCH in insects. Here we investigated the physiological response of adult Drosophila melanogaster to a gradual reduction of temperature from 25 to 0°C followed by 1h at 0°C. As expected, this RCH treatment promoted cold tolerance, and so we hypothesized that this change could be detected at the proteomic level. Using 2D-DIGE, we found that only a few proteins significantly changed in abundance, and of these, we identified a set of four proteins of particular interest. These were identified as two different variants of glycogen phosphorylase (GlyP) of which three spots were up-regulated and another was down regulated. In subsequent experiments, we quantified upstream events by measuring the GlyP mRNA amount, but we found no marked effect of RCH. We also examined downstream events by measuring GlyP activity and the level of free sugars. We found no effect of RCH on GlyP activity. On the other hand, screening of whole animal sugar contents revealed a small increase in glucose levels following RCH while trehalose content was unaltered. This study highlights a complex regulation of GlyP in relation to RCH where we found associations between the cold tolerance, the protein abundance and the metabolite concentrations but no changes in mRNA expression and enzyme activity. These data stress the necessity of combining the hypothesis-generating power of an 'Omics' approach with subsequent targeted validations across several levels of the biological organization. We discuss reasons why different biological linked levels do not necessarily change stoichiometrically.
authors: Zoophysiology, Department of Biosciences, Aarhus University, C.F. Møllers Alle 3, Building 1131, DK-8000 Aarhus C, Denmark. Electronic address: biojo@biology.au.dk.
authors: Johannes
authors: J
authors: Overgaard
authors: Genetics, Ecology & Evolution, Department of Biosciences, Aarhus University, Ny Munkegade 114-116, Building 1540, DK-8000 Aarhus C, Denmark.
authors: Jesper Givskov
authors: JG
authors: Sørensen
authors: Proteomics Core Facility Biogenouest, INSERM U1085 IRSET, Campus de Beaulieu, Université de Rennes 1, 263 Avenue du Général Leclerc CS 2407, 35042 Rennes Cedex, France.
authors: Emmanuelle
authors: E
authors: Com
authors: Université de Rennes 1, UMR CNRS 6553 Ecobio, 263 Avenue du Général Leclerc CS 74205, 35042 Rennes Cedex, France.
authors: Hervé
authors: H
authors: Colinet
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D003080:Cold Temperature; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism; D004331:Drosophila melanogaster / Q000201:enzymology / Q000235:genetics / Q000502:physiology*; D005260:Female; D024981:Glycogen Phosphorylase / Q000235:genetics / Q000378:metabolism; D008297:Male
chemical_list: D029721:Drosophila Proteins; D024981:Glycogen Phosphorylase
keywords: Acclimation; Cold tolerance; Fruit fly; Glycogen Phosphorylase; Proteomics