Molecular cloning, tissue distribution and food intake regulatory effects of ghrelin in grass carp (Ctenopharyngodon idellus)

Ghrelin is one of vital brain-gut peptides involved in feeding regulation in vertebrates, and is well known for its appetite-stimulating capacity. Nucleotide sequences of ghrelin gene were identified both at DNA and cDNA levels, using homology-based cloning techniques from grass carp (Ctenopharyngodon idellus). The 506 bp full-length ghrelin cDNA consists of a 90 bp 5′-untranslated region, a 312 bp open reading frame and a 104 bp 3′-untranslated region. The 103-amino acid prepropeptide encoded by open reading frame turns into a mature peptide with 19 amino acids after posttranslational modification. putative amino acid sequence analysis among vertebrates indicated that grass carp ghrelin showed the highest sequence homology with teleosts, and lower homology with other vertebrates. Comparison of the mature amino acid sequences revealed a conserved biological active core of ghrelin in grass carp. Genomic organization of grass carp ghrelin was composed of four exons and three introns, which was similarto that of most of teleostean species. qPCR results revealed that ghrelin was highly expressed in the fore-gut and spleen with much lower levels of expression in other tissues including brain, kidney, liver, muscle, skin and air bladder. The expression pattern that decreased in a short period of time after satiation, increased thereafter as starved time went on and kept at a high level implicated ghrelin in the orexigenic effect, as a signal of meal initiation, on short-term dietary intake in grass carp.