Molecular cloning of the amino acid transporter b0,+AT cDNA from the orange-spotted grouper (Epinephelus coioides) and the effect of arginine on its expression

In this study, we obtained the full-length cDNA sequence of SLC7A9 composed by 1808 bp with an open reading frame of 1509 bp encoding 502 amino acids. Sequence alignment and phylogenetic analysis showed that most fish and higher vertebrates were highly conserved (62%-85%). b(0,+)AT mRNA was detected by real-time quantitative PCR (RT-qPCR) in brain, kidney, liver, foregut, midgut, hindgut, spleen, heart and muscle of E. coioides, and the highest expression was found in the hindgut, which was significantly higher than other groups (p < .05), followed by the kidney, midgut and liver. In order to determine whether the dietary arginine level affected the b(0,+)AT mRNA expression in grouper, the levels of b(0,+)AT gene expression in the hindgut, kidney and liver were quantified after an 8-week feeding experiment. In the hindgut, the transcript level of the b(0,+)AT gene was upregulated up to dietary arginine concentrations 29.5g/kg with a decline thereafter. However, the accurate transport characterization and function of b(0,+)AT in fish is still not clear. Further studies are needed to clarify the underlying mechanism of b(0,+)AT function in E. coioides.