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Title: Effects of short term growth hormone treatment on the rainbow trout (Oncorhynchus mykiss) liver and muscle transcriptomes

Author
item Gahr, Scott
item Vallejo, Roger
item Weber, Gregory - Greg
item Shepherd, Brian
item Silverstein, Jeffrey
item Rexroad, Caird

Submitted to: Physiological Genomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/4/2007
Publication Date: 2/19/2008
Citation: Gahr, S.A., Vallejo, R.L., Weber, G.M., Shepherd, B.S., Silverstein, J., Rexroad III, C.E. 2008. Effects of short term growth hormone treatment on the rainbow trout (Oncorhynchus mykiss) liver and muscle transcriptomes. Physiological Genomics. 32:380-9.

Interpretive Summary: Somatic growth, defined as the increase in body size or weight, is regulated by the interaction of external (environmental and nutritional) and endogenous (hormonal) stimuli. Growth hormone (GH) has a fundamental role in the somatic growth in the rainbow trout (Oncorhynchus mykiss). The primary objective of this experiment was to use microarrays to quantify the short term (3-day) effects of GH administration on gene expression in the liver and muscle in rainbow trout selected for growth rate. Additionally, we have attempted to determine the whole organism modulation in gene expression by measuring the transcript abundance in eight different tissues with real time PCR, using both previously identified growth related genes and those identified using the microarray. We identified a total of 180 genes augmented by the short term GH treatment, which are related to metabolism, immune function and iron homeostasis. We are the first to report the up regulation of the rainbow trout growth hormone receptor expression in the liver, muscle and stomach following growth hormone administration. Additionally, the effects of GH on proliferation and differentiation of the cells can be seen the modulation of expression of the myostatin genes following GH treatment. The information gathered in the current study provides a glimpse into the acute response of the growing rainbow trout to growth hormone, and may allow for the identification of early response genes regulating growth and development in the rainbow trout.

Technical Abstract: Numerous studies have established that recombinant bovine Somatotropin (rbST, aka bovine growth hormone) stimulates growth in the rainbow trout. However, the effects of rbST on target tissue gene expression are not well characterized. In the current study, we used Posilac® (Monsanto Co., St. Louis, MO) to assess the effects of rbST treatment on liver and muscle transcript levels in fish. Transcript abundance was measured in the current study using the GRASP 16 K cDNA microarray. Rainbow trout were selected from four families, two characterized as high growth rate and two as low growth rate. A total of 180 transcripts were identified as differentially expressed across tissues and growth rate. The largest proportion of the transcripts represented novel transcripts; immune and metabolism related genes represented the next largest contribution. The immune related genes were primarily modulated in the liver and indicate activation of a non-specific immune response in the rainbow trout following GH treatment. The metabolic genes include lipid metabolism, oxidative phosphorylation and one carbon metabolism pathway transcripts. A selection of the genes identified with the microarray and insulin-like growth factors, growth hormone receptors and myostatin transcripts were measured in the brain, kidney, intestine, stomach, gill and heart following GH administration. In general, transcripts identified as differentially regulated in the muscle on the microarray showed similar direction of expression in other extra-hepatic tissues. Our results indicate that short term GH treatment activates the immune system, shifts the metabolic impetus, and modulates growth regulating genes.