Submitted to: General and Comparative Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/21/2005
Publication Date: 4/26/2005
Citation: Kaiya, H., Small, B.C., Bilodeau, A.L., Shepherd, B.S., Kojima, M., Hosoda, H., Kangawa, K. 2005. Purification, cdna cloning and characterization of ghrelin in channel catfish, ictalurus punctatus. General and Comparative Endocrinology 143:201-210. Interpretive Summary: The peptide ghrelin stimulates growth hormone (GH) production and plays a central role in the regulation of feed intake. The actions of ghrelin on GH production and feeding are of particular importance to researchers working to enhance channel catfish growth and feed efficiency. Channel catfish are the most extensively cultured food-fish species in North America, and improvements in growth and feed efficiency are of considerable importance to the United States catfish industry since improved production efficiency would improve global competitiveness. The present research describes the discovery and isolation of the ghrelin peptide and cDNA from the stomach of channel catfish, and demonstrates that ghrelin is a potent stimulator of GH production in catfish. Application of this knowledge in a selective breeding program might lead to future improvements in channel catfish production efficiency.
Technical Abstract: The ghrelin peptide and cDNA encoding precursor protein were isolated from the stomach of a channel catfish, Ictalurus punctatus. Catfish ghrelin is a 22-amino acid peptide with a sequence of GSSFLSPTQKPQNRGDRKPPRV. The third serine residue has been modified by n-decanoic acid and unsaturated fatty acids; however, an octanoylated form could not be identified. The carboxyl end of the peptide possessed an amide structure. A Gly-extended, non-amidated 23-amino acid ghrelin (ghrelin-Gly) was also isolated. Real-time quantitative PCR analysis revealed high levels of gene expression in the stomach, moderate levels in the pancreas and gall bladder, and low levels in the pituitary, gill, intestine, and trunk kidney. Intraperitoneal (IP) injection of ghrelin increased plasma GH levels in the catfish, but the effect of ghrelin-Gly was more potent than that of amidated ghrelin. Furthermore, IP injection with both amidated ghrelin and ghrelin-Gly caused a significant in pituitary GH mRNA expression over a 3-h period. These results indicate that ghrelin is present in catfish and stimulates GH gene expression and GH release in channel catfish.