Acclimatory responses of the Daphnia pulex proteome to environmental changes. II. Chronic exposure to different temperatures (10 and 20 degrees C) mainly affects protein metabolism.
BACKGROUND
Temperature affects essentially every aspect of the biology of poikilothermic animals including the energy and mass budgets, activity, growth, and reproduction. While thermal effects in ecologically important groups such as daphnids have been intensively studied at the ecosystem level and at least partly at the organismic level, much less is known about the molecular mechanisms underlying the acclimation to different temperatures. By using 2D gel electrophoresis and mass spectrometry, the present study identified the major elements of the temperature-induced subset of the proteome from differently acclimated Daphnia pulex.


RESULTS
Specific sets of proteins were found to be differentially expressed in 10 degrees C or 20 degrees C acclimated D. pulex. Most cold-repressed proteins comprised secretory enzymes which are involved in protein digestion (trypsins, chymotrypsins, astacin, carboxypeptidases). The cold-induced sets of proteins included several vitellogenin and actin isoforms (cytoplasmic and muscle-specific), and an AAA+ ATPase. Carbohydrate-modifying enzymes were constitutively expressed or down-regulated in the cold.


CONCLUSIONS
Specific sets of cold-repressed and cold-induced proteins in D. pulex can be related to changes in the cellular demand for amino acids or to the compensatory control of physiological processes. The increase of proteolytic enzyme concentration and the decrease of vitellogenin, actin and total protein concentration between 10 degrees C and 20 degrees C acclimated animals reflect the increased amino-acids demand and the reduced protein reserves in the animal's body. Conversely, the increase of actin concentration in cold-acclimated animals may contribute to a compensatory mechanism which ensures the relative constancy of muscular performance. The sheer number of peptidase genes (serine-peptidase-like: > 200, astacin-like: 36, carboxypeptidase-like: 30) in the D. pulex genome suggests large-scaled gene family expansions that might reflect specific adaptations to the lifestyle of a planktonic filter feeder in a highly variable aquatic environment.
Schwerin
Susanne
S
Institute of Zoophysiology, University of Münster, Münster, Germany. susanne.schwerin@freenet.de
Zeis
Bettina
B
Lamkemeyer
Tobias
T
Paul
Rüdiger J
RJ
Koch
Marita
M
Madlung
Johannes
J
Fladerer
Claudia
C
Pirow
Ralph
R
D000064:Acclimatization / Q000502:physiology*; D000595:Amino Acid Sequence; D000818:Animals; D003080:Cold Temperature; D003598:Cytoskeletal Proteins / Q000096:biosynthesis / Q000235:genetics; D003621:Daphnia / Q000502:physiology*; D015180:Electrophoresis, Gel, Two-Dimensional; D004777:Environment; D005786:Gene Expression Regulation; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000096:biosynthesis / Q000235:genetics; D010447:Peptide Hydrolases / Q000096:biosynthesis / Q000235:genetics; D014176:Protein Biosynthesis; D020543:Proteome; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013696:Temperature; D014819:Vitellogenins / Q000096:biosynthesis / Q000235:genetics
D003598:Cytoskeletal Proteins; D009124:Muscle Proteins; D020543:Proteome; D014819:Vitellogenins; D010447:Peptide Hydrolases