Molecular cloning, characterization and expression profiles of multiple leptin genes and a leptin receptor gene in orange-spotted grouper (Epinephelus coioides).

Leptin plays key roles in body weight regulation, energy metabolism, food intake, reproduction and immunity in mammals. However, its function in teleosts is still unclear. In the present study, two leptin genes (gLepA and gLepB) and one leptin receptor gene (gLepR) were cloned and characterized in orange-spotted grouper (Epinephelus coioides). The cDNAs of gLepA and gLepB were 671 bp and 684 bp in length, encoding for proteins of 161 amino acid (aa) and 158 aa, respectively. The three-dimensional (3D) structures modeling of gLepA and gLepB showed strong conservation of tertiary structure with that of other vertebrates. The total length of gLepR cDNA was 4242 bp, encoding a protein of 1169 aa which contained all functionally important domains conserved among vertebrate LEPR. Tissue distribution analysis showed that gLepA was highly expressed in cerebellum, liver and ovary, while gLepB mRNA abundantly in the brain regions, as well as in the ovary with some extend. The gLepR was mainly expressed in kidney, head kidney and most of brain regions. Analysis of expression profiles of gLep and gLepR genes during the embryonic stages showed that high expression of gLepR was observed in the brain vesicle stage, while neither gLepA nor gLepB mRNA was detected during different embryonic stages. Finally, fasting and refeeding experiments were carried out to investigate the possible function of leptin genes in food intake and energy metabolism, and the results showed that a significant increase of gLepA expression in the liver was induced by food deprivation in both short-term (7 days) and long-term (3 weeks) fasting and gLepA mRNA upregulation was eliminated after refeeding, while gLepB wasn't detected in the liver of grouper during fasting. No significant differences in hypothalamic leptin and leptin receptor expression were found during short-term fasting and refeeding. Hepatic expression of gLepA mRNA increased significantly 9h after a single meal. These results suggested gLepA, other than gLepB, functioned in the regulation of energy metabolism and food intake in this Perciform fish.