Molecular cloning and expression characteristics of ghrl and ghsr genes in bighead carp (Hypophthalmichthys nobilis)

Abstract

Backgroud Ghrelin (ghrl) and its receptor gene, ghsr (growth hormone secretagogue receptor), regulate numerous physiological functions, including growth hormone secretion and food intake. In the present study, we investigated the sequences and expression characteristics of the two genes in bighead carp (Hypophthalmichthys nobilis). Methods Cloning and expression characteristics of the ghrl and ghsr gene were got and analyzed by using the RACE technique, qRT-PCR, and in situ hybridization. The sizes of the experimental fish were 1.21 ± 0.20 kg in winter (6–7 months old) and 2.34 ± 0.20 kg in summer (18–19 months old). Results The ghrl and ghsr genes, encoded 106 and 346 amino acids, respectively, and were 1208 bp and 2239 bp in length. Early blastocysts had the highest levels of ghrl and ghsr expression throughout early development (P < 0.01). The gut exhibited the highest levels of expression of ghrl, whereas significantly higher levels of ghsr (P < 0.01) were detected in the brain. Significantly higher levels of expression of ghrl and ghsr were detected in the intestine and muscle in summer, when compared with the levels in winter (P < 0.05). Based on in situ hybridization, intestine ghrl expression signals were more pronounced than intestinal ghsr expression signals, whereas ghsr expression signals were higher than those of ghrl in brain tissues. The co-expression patterns of related genes in the growth hormone synthesis, secretion and action pathway (ko04935), and cAMP signaling pathway (ko04024) also indicated that ghrl and ghsr are involved in the feeding regulation of bighead fish. Conclusion Our findings suggest that ghrl and ghsr potentially play roles in bighead carp feeding and associated energy metabolism activities, in addition to growth performance.