Submitted to: Biomed Central (BMC) Genomics
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/29/2007
Publication Date: 9/19/2007
Citation: Salem, M., Silverstein, J., Rexroad III, C.E., Jianbo, Y. Effect of starvation on global gene expression and proteolysis in rainbow trout (Oncorhynchus mykiss). Biomed Central (BMC) Genomics. 8:328. Interpretive Summary: A major constraint to increasing fish production efficiency is the lack of genetically improved strains of fish for aquaculture. Selection for improved feed efficiency could increase profitability of the aquaculture industry. However, none of the existing fish-breeding programs use feed efficiency in their selection index. Instead, they select for rapid growth at a fixed age. It is challenging and costly to record individual feed intake from a large population of fish. Genetic marker-assisted selection could be used to facilitate selection efforts for improved feed efficiency. Variation in feed efficiency is a result of complex interactions between genetically determined components and a wide range of environmental influences including nutrition. An effective way to identify the relationships between major metabolic pathways and body processes is to examine changes in metabolism during starvation. The primary objective of this study was to use microarray chip technology to identify metabolic adaptations of liver tissue during nutritional restrictions in rainbow trout (RBT). This study demonstrated that the metabolic capacity of the liver was significantly influenced at the expression level by food availability. For example, genes associated with tissue metabolism, protein synthesis, and liver fatty acid transport were all decreased while those involved with mobilization of protein reserves were increased. The use of microarray and enzyme assays together has provided a glimpse of metabolic changes during starvation which will help identify those steps that most affect nutrient utilization.
Technical Abstract: Background Growth and feed efficiency are key traits in selecting superior animals for genetic improvement programs. Fast, efficiently growing animals have increased protein synthesis and/or reduced protein degradation relative to slow, inefficiently growing animals. Microarray expression profiling allows for the detailed characterization of the genes/pathways that regulate processes of protein turnover. Results We evaluated changes in hepatic global gene expression in response to 3-week starvation in rainbow trout. Microarray analysis revealed a coordinated, down-regulated expression of protein biosynthesis genes in starved fish. In addition, genes of lipid metabolism/transport, aerobic respiration, blood functions and immune response were decreased in response to starvation. However, the microarray approach did not reveal a significant increase of gene expression in protein catabolic pathways. Further studies using real-time PCR and enzyme activity assays were performed to investigate the gene expression patterns of the major proteolytic pathways, cathepsins, calpains and the multi-catalytic proteasome. Feed restriction reduced mRNA accumulation of the calpain inhibitor, calpastatin (CAST), with a subsequent increase in the calpain catalytic activity. In addition, starvation caused a slight but significant increase in 20S proteasome activity without affecting mRNA levels of the proteasome genes suggesting a post-transcriptional action. Starvation did not affect activities or mRNA accumulation of cathepsin D and L. Conclusion These results suggest a significant role of calpain and 20S proteasome pathways in protein mobilization as a source of energy during fasting and a potential association of the CAST gene with fish growth efficiency.