Expression of a duplicate Na,K-ATPase β₁-isoform in the European eel (Anguilla anguilla)

Recent studies on teleost fish have suggested that their genomes have undergone ancient polyploidization events resulting in the duplication of the genome. A duplicate copy of the Na,K-ATPase β ₁-isoform (called β ₂₃₃) has been identified in the European eel (Anguilla anguilla). The β ₂₃₃-isoform shares high levels of nucleotide (74.8%) and amino acid (69.9%) homology with the eel β ₁-subunit as well as other vertebrate β ₁-sequences. Compared with the widely expressed β ₁-isoform, expression of β ₂₃₃-mRNA is mainly restricted to epithelial tissues. Seawater acclimation induced increases in β ₂₃₃-mRNA levels in kidney, gill, and intestine of migratory 'silver' but not the nonmigratory 'yellow' adult eels, suggesting that the factors responsible for this upregulation are themselves developmentally regulated. Expression of a variably glycosylated 40- to 52-kDa β ₂₃₃-protein in both gill 'chloride' and intestinal epithelial cells suggests that the β ₂₃₃-isoform of Na,K-ATPase may play an important functional role in the major osmoregulatory tissues of euryhaline fish such as the eel.