Submitted to: Comparative Biochemistry and Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/27/2009
Publication Date: 8/22/2009
Publication URL: http://handle.nal.usda.gov/10113/55422
Citation: Small, B.C., Quiniou, S., Kaiya, H. 2009. Sequence, genomic organization and expression of two channel catfish, Ictalurus punctatus, Ghrelin receptors. Comparative Biochemistry and Physiology. 154(4):451-464. 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 to improve global competitiveness. In the present study we sought to identify receptor genes in channel catfish known to regulate how ghrelin affects growth, feeding, and metabolism in other animals, and to assess how these receptor genes respond to different forms of catfish ghrelin. The genes were successfully isolated from channel catfish and were found to be differentially regulated as a result of tissue type and form of ghrelin. These results provide new information about the control of catfish growth and metabolic efficiency, and, as such, catfish ghrelin receptors are being looked at as possible markers for selecting faster growing catfish as part of a selective breeding program.
Technical Abstract: Two ghrelin receptor (GHS-R) genes were isolated from channel catfish tissue and a bacterial artificial chromosome (BAC) library. The two receptors were characterized by determining tissue distribution, ontogeny of receptor mRNA expression, and effects of exogenous homologous ghrelin administration on target tissue mRNA expression. Analysis of sequence similarities indicated two genes putatively encoding GHS-R1 and GHS-R2, respectively, which have been known to be present in zebrafish. Organization and tissue expression of the GHS-R1 gene was similar to that reported for other species, and likewise yielded two detectable mRNA products as a result of alternative splicing. Expression of both full-length, GHS-R1a, and splice variant, GHS-R1b, mRNA was highest in the pituitary. Gene organization of GHS-R2 was similar to GHS-R1, but a splice variant, GHS-R2b, was not identified. Expression of GHS-R2a mRNA was highest in the Brockman bodies. GHS-R1a mRNA was detected in unfertilized eggs and throughout embryogenesis, whereas GHR-R2a mRNA was not expressed in unfertilized eggs or early developing embryos and was the highest at the time of hatching. Catfish intraperitoneally injected with catfish ghrelin-Gly had greater mRNA expression of GHS-R1a in pituitaries at 2-h and Brockman bodies at 4 h, and of GHSR2a in Brockman bodies at 6 h post injection. Amidated catfish ghrelin (ghrelin-amide) had no observable effect on expression of either pituitary receptor; however, GHS-R1a and GHS-R2a mRNA expression levels were increased 4 h post injection of ghrelin-amide in Brockman bodies. This is the first characterization of GHS-R2a and suggests regulatory and functional differences between the two catfish receptors.