Ghrelin cDNA structure and expression profile in early development of largemouth bass(Micropterus salmoides)

Ghrelin,the endogenous ligand of growth hormone secretagogue receptor(GHS-R) ,has been shown to play an important role in eliciting growth hormone release and energy homeostasis.In the present study,we cloned ghrelin from stomach tissue of largemouth bass(Micropterus salmoides) by using RT-PCR,RACE and PCR method.The amplified cDNA was totally 434bp in length including 321bp open reading frame(ORF) .It encoded a propeptide of 107aa,with the predicted mature peptide consisting of 20aa.Alignment analyses showed that the similarities of propeptide and mature peptide beween Dicentrarchus labrax were 85% and 90% respectively.To better understand the expression during fish early development of ghrelin,we also detected the expression profile of ghrelin at embryo and early fry of largemouth bass by real-time PCR.The result showed that ghrelin mRNA was observed at fertilized egg stage,and increased at metamere stage.The expression level at 4-days and 12-days larvae was about 206.77 and 531.20 times higher than that at fertilized egg stage.The 4-days larva was"first-feeding"in largemouth bass,when the larva was from endogenous nutrition to exogenous nutrition phase.The 12-day larvae had greatly increased intake appetite and at this stage larvae took full advantage of the exogenous nutrition,and the expression of ghrelin also reached the highest value.These results combined suggest that ghrelin is involved in the regulation of food intake in largemouth bass.