Acclimatory responses of the Daphnia pulex proteome to environmental changes. I. Chronic exposure to hypoxia affects the oxygen transport system and carbohydrate metabolism.
BACKGROUND
Freshwater planktonic crustaceans of the genus Daphnia show a remarkable plasticity to cope with environmental changes in oxygen concentration and temperature. One of the key proteins of adaptive gene control in Daphnia pulex under hypoxia is hemoglobin (Hb), which increases in hemolymph concentration by an order of magnitude and shows an enhanced oxygen affinity due to changes in subunit composition. To explore the full spectrum of adaptive protein expression in response to low-oxygen conditions, two-dimensional gel electrophoresis and mass spectrometry were used to analyze the proteome composition of animals acclimated to normoxia (oxygen partial pressure [Po2]: 20 kPa) and hypoxia (Po2: 3 kPa), respectively.


RESULTS
The comparative proteome analysis showed an up-regulation of more than 50 protein spots under hypoxia. Identification of a major share of these spots revealed acclimatory changes for Hb, glycolytic enzymes (enolase), and enzymes involved in the degradation of storage and structural carbohydrates (e.g. cellubiohydrolase). Proteolytic enzymes remained constitutively expressed on a high level.


CONCLUSIONS
Acclimatory adjustments of the D. pulex proteome to hypoxia included a strong induction of Hb and carbohydrate-degrading enzymes. The scenario of adaptive protein expression under environmental hypoxia can be interpreted as a process to improve oxygen transport and carbohydrate provision for the maintenance of ATP production, even during short episodes of tissue hypoxia requiring support from anaerobic metabolism.
Zeis
Bettina
B
Institute of Zoophysiology, University of Münster, Münster, Germany. zeis@uni-muenster.de
Lamkemeyer
Tobias
T
Paul
Rüdiger J
RJ
Nunes
Frank
F
Schwerin
Susanne
S
Koch
Marita
M
Schütz
Wolfgang
W
Madlung
Johannes
J
Fladerer
Claudia
C
Pirow
Ralph
R
D000064:Acclimatization / Q000502:physiology*; D000818:Animals; D050260:Carbohydrate Metabolism; D003621:Daphnia / Q000187:drug effects / Q000502:physiology*; D015180:Electrophoresis, Gel, Two-Dimensional; D005786:Gene Expression Regulation / Q000187:drug effects; D006026:Glycoside Hydrolases / Q000096:biosynthesis / Q000235:genetics; D006454:Hemoglobins / Q000096:biosynthesis / Q000235:genetics; D000860:Hypoxia / Q000378:metabolism; D013058:Mass Spectrometry; D010100:Oxygen / Q000378:metabolism*; D010313:Partial Pressure; D010447:Peptide Hydrolases / Q000096:biosynthesis / Q000235:genetics; D011134:Polysaccharides / Q000378:metabolism; D020543:Proteome / Q000187:drug effects*
D006454:Hemoglobins; D011134:Polysaccharides; D020543:Proteome; D006026:Glycoside Hydrolases; D010447:Peptide Hydrolases; D010100:Oxygen