Oxygen-induced changes in hemoglobin expression in Drosophila

The hemoglobin gene 1 (dmeglob1) of the fruit fly Drosophila melanogaster is expressed in the tracheal system and fat body, and has been implicated in hypoxia resistance. Here we investigate the expression levels of dmeglob1 and lactate dehydrogenase (a positive control) in embryos, third instar larvae and adult flies under various regimes of hypoxia and hyperoxia. As expected, mRNA levels of lactate dehydrogenase increased under hypoxia. We show that expression levels of dmeglob1 are decreased under both short- and long-term hypoxia, compared with the normoxic (21% O-2) control. By contrast, a hypoxia/reoxygenation regime applied to third instar larvae elevated the level of dmeglob1 mRNA. An excess of O-2 (hyperoxia) also triggered an increase in dmeglob1 mRNA. The data suggest that Drosophila hemoglobin may be unlikely to function merely as a myoglobin-like O-2 storage protein. Rather, dmeglob1 may protect the fly from an excess of O-2, either by buffering the flux of O-2 from the tracheoles to the cells or by degrading noxious reactive oxygen species.