Identification and Genomic Sequence of a Ghrelin Receptor (GHS-R)-like Receptor in the Mozambique Tilapia, Oreochromis mossambicus.

Abstract

The growth hormone secretagogue-receptor (GHS-R) is an endogenous receptor for the gut hormone ghrelin (GRLN). Two isoforms of GHS-R have been identified in several animals: functional GHS-R1a and a splice variant of unknown function, GHS-R1b. Here we report identification of a GHS-R-like receptor (GHSR-LR) in the Mozambique tilapia, Oreochromis mossambicus. The cDNA is 1584 bp in length and encodes a 384-amino acid GHS-R1a ortholog. The amino acid sequence of tilapia GHS-R1a is 54, 60, 80 and 89% identical to that of rat, chicken, pufferfish, and seabream GHS-R1a, respectively. Genomic PCR revealed that the tilapia GHS-R gene is composed of two exons separated by a single intron. In addition, a GHS-R1b ortholog, which is generated by alternative splicing of the GHS-R gene and contains part of the intron, was identified and predicted to be a 298-amino acid protein. Functional analyses of tilapia GHS-R1a were conducted using mammalian HEK 293 and CHO cells, but the expected increase in intracellular calcium ions by tilapia or rat GRLN was not observed. We found that the GHS-R1a ortholog is expressed in greater quantities than the GHS-R1b ortholog in all tissues assayed. Further studies are required to conclude that our identified protein is the GHS-R for tilapia, although the gene structure and amino acid sequence showed high similarities to other GHS-R genes; thus, we designated this protein GHSR-LR.