WRIGHT, P.A.; MORGAN, R.L.; CAMPBELL, A.; ROSENBERGER, A.G.; MURRAY, B.W.; UNIVERSITY OF GUELPH; UNIVERSITY OF GUELPH; UNIVERSITY OF GUELPH; UNIVERSITY OF GUELPH; UNIVERSITY OF NORTHERN BRITISH COLUMBIA: Expression of two arginase genes in rainbow trout: tissue differences and up-regulation with fasting

Arginase is a multifunctional enzyme in nitrogen metabolism. There are two forms of arginase in terrestrial vertebrates (ureotelic) encoded by separate genes, ARG01 (cytosolic, hepatic) and ARG02 (mitochondrial, non-hepatic). In ammoniotelic fish (eg., rainbow trout, Oncorhynchus mykiss) without a hepatic urea cycle, arginase catalyses the conversion of dietary arginine to urea and ornithine. Trout arginase activity is largely mitochondrial. We predicted, therefore, that the arginase gene(s) in trout would be more similar to the mammalian ARG02 gene. Using PCR cloning techniques, we characterized the full (1221 bp) and partial (196 bp) coding region of two rainbow trout arginase genes (Onmy-ARG01 and ARG02). In contrast to our prediction, the nucleic acid sequences for Onmy-ARG01 and Onmy-ARG02 aligned with the mammalian ARG01 and ARG02 genes, respectively. Using Northern analysis, we determined the pattern of mRNA expression between various trout tissues. Onmy-ARG01 was expressed in liver and intestine. Onmy-ARG02 was expressed in liver, kidney, gill, heart, intestine, white muscle and red muscle. There was a 3-fold increase in liver arginase activity and a 2-fold increase in Onmy-ARG01:beta-actin mRNA levels, but no change in Onmy-ARG02 mRNA levels in juvenile fish fasted 6 weeks relative to fed fish. These findings indicate that trout arginase genes are differentially expressed and in response to dietary stress, differentially regulated.