Molecular characterization and expression profiles of leptin receptor in grass carp (Ctenopharyngodon idella)

Leptin receptor (LEPR) is a type of transmembrane receptor and a member of the class I cytokine receptor family that plays a decisive role in the physiological functions mediated by leptin. In this study, a fish LEPR gene (CiLEPR) was cloned from Ctenopharyngodon idella. The open reading frame (ORF) sequence of the CiLEPR gene included 3504 bp, which encoded 1078 amino acids that formed six functional domains, including five FN3 domains and a lep_receptor_Ig domain. Phylogenetic analysis showed that the CiLEPR amino acid sequence was closely related to that of LEPR from Hypophthalmichthys molitrix. The qRT-PCR results showed that the CiLEPR gene was widely expressed in all investigated tissues of C. idella and was relatively highly expressed in the gills. The results of the circadian rhythm experiment revealed that the intestinal expression of the CiLEPR gene changed regularly over time. In C. idella intestinal cell experiments, it was observed that recombinant leptin could upregulate the expression levels of CiLeptin, CiLEPR and CiPepT1 in the intestines of C. idella. The results of experiments in which fish were fed with various protein sources demonstrated that the mRNA expression levels of CiLeptin, CiLEPR and CiPepT1 in the fish meal group were higher than those in the soybean meal group at 28 d. The data indicated that C. idella fed diets with medium amounts of dietary protein (37%) expressed the highest mRNA levels of CiLeptin, CiLEPR and CiPepT1 after 4 weeks. These results provide a basis for further studies on the nutritional regulation and physiological functions of leptin receptors in fish.