Sequence, genomic organization and expression of ghrelin receptor in grass carp, Ctenopharyngodon idellus

The growth hormone secretagogue-receptor (GHS-R) is an endogenous receptor for the gut hormone ghrelin. Here we report the identification and characterization of GHS-R1a in grass carp, Ctenopharyngodon idellus. The full-length GHS-R1a cDNA contained a 1803-bp coding domain sequence which encoded a peptide of 360 amino acid residues. Comparison analysis revealed that the amino acid sequences of GHS-R1a were highly conserved in vertebrates and shared 97% amino acid identity with zebrafish (Danio rerio), 96% with jian carp (Cyprinus carpio var. Jian) and 93% with goldfish (Carassius auratus). The GHS-R1a showed the highest level of mRNA expression in the pituitary, followed by the brain and liver, and the lowest expression was observed in the hindgut. Intraperitoneally injected with grass carp ghrelin (50, 100 and 150 ng/g body weight (BW)), grass carp showed greater mRNA expression of GHS-R1a in the pituitary compared with saline injected at 0.5 h postinjection. It was observed that food deprivation could promote the expression of ghrelin and GHS-R1a in the pituitary, demonstrating that nutritional status can influence the expression of both ghrelin and GHS-R1a in the pituitary. After a 2- or 4-week fast, plasma growth hormone (GH) increased, was positively correlated with ghrelin and GHS-R1a mRNA expression levels in the pituitary. These results suggested that the involvement of ghrelin/GHS-R1a systems in mediating the effects of nutritional status and ghrelin on growth processes in grass carp.