Cloning and sequence analysis of common carp (Cyprinus carpio) gip and the regulation of its mRNA expression

As an important incretin, GIP (glucose-dependent insulinotropic polypeptide) is involved in regulation of glucose uptake and lipid deposition. To investigate the role of Gip in Cyprinus carpio, the gip was cloned from the foregut by RT-PCR (reverse transcription-polymerase chain reaction). The sequence was analyzed by bioinformatics and the mRNA expression was detected by Real-time PCR. The result showed that the ORF (Open reading frame) of C. carpio gip is 324 bp, which encodes 107 amino acids. Based on amino acids sequence, the structure of Gip precursor protein contains four domains: signal peptide, N-terminal domain, mature Gip peptide and C-terminal domain. The result of sequence alignment and phylogenetic tree showed that the identity of C. carpio Gip protein was the closest to that of D. rerio. The Real-time PCR result showed that the gip was widely expressed in multiple tissues, and had higher expression in the intestine and pituitary of C. carpio. In OGTT experiment, the gip expression was significantly increased in C. carpio foregut and brain after glucose treatment. In the fasting and refeeding experiment, the gip expression in the foregut was markedly decreased after fasting for 7 days, and was significantly increased after refed. In the feeding experiment, the gip expression level was increased in the high glucose and high lipid groups. In this study, C. carpio gip was cloned, and the expression level was regulated by nutrient status. The results provide the data base for illustrating Gip biological functions and theoretical foundation for investigating the regulation of glucose and lipid metabolism in fish.