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First published online May 18, 2006
Journal of Experimental Biology 209, 2129-2137 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02243
Hypoxia induces a complex response of globin expression in zebrafish (Danio rerio)
1 Institute of Zoology, University of Mainz, D-55099 Mainz,
Germany
2 Institute of Molecular Genetics, University of Mainz, D-55099 Mainz,
Germany
* Author for correspondence (e-mail: burmeste{at}uni-mainz.de)
Accepted 29 March 2006
Unlike most mammals, many fish species live and survive in environments
with low or changing levels of oxygen. Respiratory proteins like hemoglobin or
myoglobin bind or store oxygen, thus enhancing its availability to the
respiratory chain in the mitochondria. Here we investigate by means of
quantitative real-time PCR the changes of hemoglobin, myoglobin, neuroglobin,
cytoglobin and globin X mRNA in zebrafish (Danio rerio) exposed to
mild (PO2=
8.6 kPa) or severe
(PO2=
4.1 kPa) hypoxia. Neuroglobin and myoglobin
protein levels were investigated by western blotting. Whereas mild hypoxia
caused only minor changes of mRNA levels, strong hypoxia enhanced mRNA levels
of the control genes (lactate dehydrogenase A and phosphoglycerate kinase 1).
Surprisingly, levels of hemoglobin
and ß mRNA were significantly
reduced under severe hypoxia. Myoglobin mRNA and protein in heart mildly
increased, in line with its proposed oxygen supply function. Likewise,
neuroglobin mRNA and protein significantly increased in brain (up to 5.7-fold
at the protein level), but not in eye. This observation, firstly, suggests
physiological differences of zebrafish eye and brain under hypoxia, and
secondly, indicates an important role of neuroglobin in oxidative metabolism,
probably oxygen supply within neurons. There was little change in the
expression of the two cytoglobin genes. Globin X mRNA significantly decreased
under hypoxia, pointing to a functional linkage to oxygen-dependent
metabolism.
Key words: cytoglobin, hemoglobin, myoglobin, neuroglobin, oxygen, zebrafish, Danio rerio
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