Meeting Abstract

11.3  Jan. 4  Rainbow Trout Possess Two Proinsulin-Encoding mRNAs that are Differentially Expressed CARUSO*, M.A.*; SHERIDAN, M.A.; North Dakota State Univ., Fargo Michael.Caruso@ndsu.edu

Insulin plays an important role in the growth, development, and metabolism of vertebrates. Growing evidence suggests that some species of vertebrates possess two insulin genes; however, the phylogenetic distribution and the physiological significance of this phenomenon are not known. In this study, rainbow trout were used to examine further the polygenic origins of insulin. Two unique cDNAs that encode proinsulin were isolated, cloned, and sequenced from the endocrine pancreas (Brockman body). One 558-bp cDNA encodes a 105-amino acid protein (INS 1) and the other 571-bp cDNA encodes a 107 amino acid protein (INS 2). The sequences share 87.6% nucleotide identity and 89.7% deduced amino acid identity. Quantitative real-time PCR revealed that the two INS mRNAs were differentially expressed, both in terms of distribution among tissues as well as in terms of abundance within selected tissues. INS 1 was more abundant than INS 2 in the pancreas, pyloric cecum, and adipose. Both INS 1 and INS 2 mRNA were found at low levels within the brain. The regulation of INS mRNA expression was examined in Brockman bodies of trout placed on differing nutritional regimens. Fasting for 4 weeks or for 6 weeks reduced mRNA levels of both INS 1 and INS 2 compared to fish that were continuously fed. Refeeding fish for 2 weeks after previously fasting for 4 weeks resulted in a rebound of INS mRNAs to levels near those in continuously fed fish. These findings contribute to the understanding of the evolution of the insulin gene in teleost fish. In addition, these findings indicate that the expression of the INS genes in trout is differentially regulated. (Supported by NSF IOB 0444860)