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Title: Effect of sexual maturation on muscle gene expression of rainbow trout: RNA-Seq approach

Author
item SALEM, MOHAMED - Middle Tennessee State University
item MANOR, MEGHAN - West Virginia University
item AUSSANASUWANNAKUL, AUNCHALEE - West Virginia University
item KENNEY, P.BRETT - West Virginia University
item Weber, Gregory - Greg
item YAO, JIANBO - West Virginia University

Submitted to: Physiological Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/11/2013
Publication Date: 10/1/2013
Citation: Salem, M., Manor, M.L., Aussanasuwannakul, A., Kenney, P., Weber, G.M., Yao, J. 2013. Effect of sexual maturation on muscle gene expression of rainbow trout: RNA-Seq approach. Physiological Reports. 1(5).no.e00120.DOI:10.1002/phy2.120.

Interpretive Summary: Fish growth slows and fillet quality, or muscle quality, deteriorates in many fish species when the fish develops gonads. This is primarily because fish such as rainbow trout produce gonads that can make up as much as 15-20% of the entire body weight. This tremendous growth of gonadal tissue causes nutrient mobilization as a response to the energetic over-demands of the egg/ovarian growth phase, in part at the expense of muscle. We have been investigating the mechanisms behind this fight between the gonads and muscle for nutritional resources. Recently we showed that most of the changes in muscle growth and quality starts 2-3 months before spawning. Gravid fish, those with large gonads, exhibited reduced intramuscular fat that is lower in saturated and monounsaturated fatty acids and higher in polyunsaturated fatty acids compared to sterile fish. We used RNA-Seq to explain the mechanisms underlying changes during this phase of sexual maturity. To minimize changes due to nutrient deficits, fish were fed on a high-plane of nutrition. The RNA-Seq technique identified a gene expression signature that is consistent with metabolic changes of the gravid fish. Gravid fish exhibited increased abundance of transcripts in metabolic pathways of fatty acid degradation and up-regulated expression of genes involved in biosynthesis of unsaturated fatty acids. In addition, increased expression of genes involved in the citric acid cycle and oxidative phosphorylation was observed for gravid fish. This muscle transcriptomic signature of fish fed on a high nutritional plane is quite distinct from that previously described for fish at terminal stages of maturity and suggest that female rainbow trout approaching spawning, on high nutritional planes, likely mobilize intramuscular fat rather than protein to support gonadal maturation. The results of this research will lead to improved diets and feeding strategies to improve fillet quality in larger fish and improve egg quality.

Technical Abstract: Muscle degradation occurs as a response to various pathological states that are regulated by specific molecular mechanisms. Previously, we characterized the metabolic changes of muscle deterioration of the female rainbow trout at full sexual maturity and spawning. Muscle deterioration signs of this model represent nutrient mobilization as a response to the energetic over-demands of the egg/ovarian growth phase. Our recent studies showed that most of the changes in muscle growth and quality starts 2-3 months before spawning. Gravid fish exhibited reduced intramuscular fat that is lower in saturated and monounsaturated fatty acids and higher in polyunsaturated fatty acids compared to sterile fish. In this study, RNA-Seq was used to explain the mechanisms underlying changes during this phase of sexual maturity. To minimize changes due to nutrient deficits, fish were fed on a high-plane of nutrition. The RNA-Seq technique identified a gene expression signature that is consistent with metabolic changes of the gravid fish. Gravid fish exhibited increased abundance of transcripts in metabolic pathways of fatty acid degradation and up-regulated expression of genes involved in biosynthesis of unsaturated fatty acids. In addition, increased expression of genes involved in the citric acid cycle and oxidative phosphorylation was observed for gravid fish. This muscle transcriptomic signature of fish fed on a high nutritional plane is quite distinct from that previously described for fish at terminal stages of maturity and suggest that female rainbow trout approaching spawning, on high nutritional planes, likely mobilize intramuscular fat rather than protein to support gonadal maturation.