Leptin and its receptor in turbot Scophthalmus maximus: cloning, characterization and expression response to ratios of dietary carbohydrate–lipid

In the present study, the full-length cDNA sequences of leptin (LEP) and its receptor (LEPR) from turbot Scophthalmus maximus were cloned. The cDNA of tLEP was 1126 bp in length encoding 157 amino acids. The amino acid sequence shared low identity with human LEP (18.8 %), but the three-dimensional structures of these two LEPs were strongly conserved. The deduced 1173-amino acid sequence of tLEPR was 28 % identical to human LEPR, and 82 % too range-spotted grouper LEPR, containing all functionally important domains conserved in vertebrate LEPR. Tissue distribution analysis showed that tLEP was abundantly expressed in brain, eyes and liver. The highest level of tLEPR mRNA was found in liver and kidney. After a 9-week feeding trial using diets with different ratios of carbohydrate–lipid (1:6, 1:2, 2:1 and 14:1), it was found that the increase in dietary carbohydrate-to-lipid ratios from 1:6 to 2:1 did not significantly influence tLEP and tLEPR expression in turbot liver (P > 0.05). The hepatic tLEP expression was significantly elevated in treatment with 14:1 dietary carbohydrate-to-lipid ratio (P < 0.05). The hepatic tLEPR mRNA level in group with 14:1 dietary carbohydrate-to-lipid ratio was significantly lower than that in 1:6 group (P < 0.05), but had no significant difference with the other two groups (P > 0.05). These results revealed the important relationship between dietary carbohydrate-to-lipid ratio and LEP expression in turbot.