Molecular Characterization and Expression of α‐Globin and β‐Globin Genes in the Euryhaline Flounder (Platichthys flesus)

In order to understand the possible role of globin genes in fish salinity adaptation, we report the molecular characterization and expression of all four subunits of haemoglobin, and their response to salinity challenge in flounder. The entire open reading frames of α 1-globin and α 2-globin genes were 432 and 435 bp long, respectively, whereas the β 1-globin and β 2-globin genes were both 447 bp. Although the head kidney (pronephros) is the predicted major site of haematopoiesis, real-time PCR revealed that expression of α -globin and β -globin in kidney (mesonephros) was 1.5 times higher than in head kidney. Notably, the α 1-globin and β 1-globin mRNA expression was higher than α 2-globin and β 2-globin in kidney. Expression levels of all four globin subunits were higher in freshwater- (FW-) than in seawater- (SW-)adapted fish kidney. If globins do play a role in salinity adaptation, this is likely to be more important in combating the hemodilution faced by fish in FW than the dehydration and salt loading which occur in SW.