cDNA cloning and expression of ghrelin in giant panda (Ailuropoda melanoleuca)

Ghrelin is an endogenous ligand for the growth hormone secretagogue receptor. It plays an important role in stimulating growth hormone secretion, food intake, body weight gain and gastric motility. cDNA sequences coding for ghrelin precursor protein (prepro-ghrelin) were isolated from the stomach of a giant panda. Two different mRNA sequences of ghrelin were obtained. The long open reading frame of ghrelin (354 bp) encodes a precursor protein of 117 amino acids with a 23 amino acid signal peptide. The short one (351 bp) encodes a precursor protein of 116 amino acids with the same 23 amino acid signal peptide. The presumed giant panda mature ghrelin proteins also had two forms. Comparative analysis showed that the first and the fourth amino acids (Gly and Phe) were completely conserved and the third amino acid (Ser) was also highly conserved in the mature ghrelin. RT-PCR analysis of giant panda ghrelin mRNA in various tissues revealed high level of expression in stomach, relative lower levels of expression in small intestine, liver and kidney, and no expression in thymus, spleen and heart.