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

Abstract

Muscle degradation occurs as a response to various physiological 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 (Salem et al., Physiol. Genomics 2006;28:33-45; J. Proteomics 2010;73:778-789). Muscle deterioration in this model represents nutrient mobilization as a response to the energetic overdemands of the egg/ovarian growth phase. Our recent studies showed that most of the changes in muscle growth and quality start 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. Furthermore, 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 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.

Keywords: RNA-Seq; muscle; rainbow trout; reproduction.

Figure 1

Effects of sexual maturation on female rainbow trout separable muscle percentage (A), total protein (B), fat content (C), moisture (D) and muscle shear force (E). * and ** indicate the P values <0.05 and <0.01, respectively, (LSMeans + SEM, N = 20). 2N and 3N indicate diploid and triploid fish, respectively.

Figure 2

Effects of sexual maturation on rainbow trout relative amounts of the total saturated fatty acids (A), total unsaturated fatty acids (B), polyunsaturated fatty acids (C), alpha-linolenic acid [ALA] (D) and docosahexaenoic acid [DHA] (E). * and ** indicate the P values <0.05 and <0.01, respectively (LSMeans + SEM, N = 10). 2N and 3N indicate diploid and triploid fish, respectively.

Figure 3

Quantitative real-time PCR confirmation of five genes identified by RNA-Seq as differentially expressed in muscle of gravid fish versus sterile fish. Differential expressions of four genes related to lipid metabolism (el, ehhadh, acca2, and hadhb) and an isoform of the gapdh gene were confirmed by qPCR. All genes showed statistically significant changes that are consistent with the RNA-Seq results (P < 0.05). * and ** indicate the P values <0.05 and <0.01, respectively, (LSMeans + SEM, N = 10). 2N and 3N indicate diploid and triploid fish, respectively.

Figure 4

KEGG Reference pathway: colored boxes correspond to differentially expressed genes in muscle of gravid rainbow trout fish versus sterile fish that are assigned to the fatty acid metabolic pathway. Gene annotations and expression values are provided in Table 2.