Fasting induces preproghrelin mRNA expression in the brain and gut of zebrafish, Danio rerio

Ghrelin is a gut/brain hormone with a unique acyl modification and various biological functions in fish and mammals. In addition to its possible role as a circulating orexigenic factor, ghrelin has been shown to regulate several other physiological processes in fish in a species-specific manner. The objectives of this project were to identify the zebrafish ghrelin gene organization, study tissue specific preproghrelin mRNA expression and investigate the fasting induced changes in the expression of preproghrelin mRNA in zebrafish. Our reverse transcription polymerase chain reaction (RT-PCR) analysis confirmed the predicted ghrelin sequence available in the GenBank and identified preproghrelin mRNA expression in several tissues including the brain, gut, ovary, testis, heart and gill. PCR using genomic DNA identified that the ghrelin gene in zebrafish is comprised of four exons and three introns. Quantitative (real-time) PCR studies indicate that there is a significant increase in preproghrelin mRNA expression in the brain and gut of zebrafish fasted for 3, 5 and 7 days when compared to the expression in ad libitum fed fish. Refeeding after a 7 day fast caused a significant and dramatic decrease in preproghrelin mRNA expression in the gut and brain of zebrafish. An increase in the expression of preproghrelin mRNA during fasting, and its decrease following refeeding suggests an orexigenic role for ghrelin in zebrafish. Overall, our results provide evidence for a highly conserved structure and biological actions of ghrelin in zebrafish. Further studies are required to identify the tissue specific functions of ghrelin in zebrafish.