CDNA cloning of ghrelin and ontogeny of ghrelin mRNA expression in the gastrointestinal tract of African ostrich chicks

Abstract

Ghrelin is the endogenous ligand for the growth hormone secretagogue receptor (GHS-R). The sequence of ghrelin has been determined in many species ranging from fish to mammals. The ostrich is the largest herbivorous bird in the world. Although the distribution, morphological characteristics, and developmental changes of ghrelin-producing cells in the gastrointestinal tract of African ostrich chicks have recently been determined, the sequence and structure of ghrelin and its expression in the gastrointestinal tract of African ostrich chicks have not been studied. In the present study, the sequence and structure of ghrelin and its expression in the gastrointestinal tract of African ostrich chicks were investigated by reverse-transcriptase polymerase chain reaction (RT-PCR). Results of cDNA cloning revealed that African ostrich ghrelin is composed of 28 amino acid residues and the sequence of the 7 amino acids of the N-terminal region of African ostrich ghrelin was identical with that of other birds. Ninety-day-old female African ostriches were used to investigate the expression of ghrelin in the gastrointestinal tract. The results showed that ghrelin mRNA existed in the proventriculus, gizzard, duodenum, ileum, cecum, and rectum; there was no expression in the jejunum and colon. We observed developmental changes in the ghrelin mRNA expression in the stomach and small intestine of African ostriches. The results of the present study showed that ghrelin mRNA existed on day 1 in the proventriculus, but there was no expression in other tissues. On day 45, ghrelin mRNA existed in the proventriculus, gizzard, and ileum; however, there was no expression in the duodenum and jejunum. On day 90 and 334, we detected ghrelin mRNA in the proventriculus, gizzard, duodenum, and ileum, but there was no expression in the jejunum. The results of the present study clearly demonstrate that ghrelin mRNA exists and the distribution of ghrelin mRNA in the gastrointestinal tract of African ostriches changes with age (from postnatal day 1 to day 334).