Activity of metabolic enzymes and muscle-specific gene expression in parr and smolts Atlantic salmon Salmo salar L. of different age groups

Cloning, phylogenetic and expression analysis of two MyoDs in yellowtail kingfish (Seriola lalandi)

Yellowtail kingfish (Seriola lalandi) is a pelagic piscivore distributed circumglobally. Owing to its great market value, the growth mechanism of S. lalandi, including muscle development and growth, is a hot research topic. The myoblast determination protein (MyoD) gene has been shown to play an important role in formation of myoblasts and the function of somites in fish. The open reading frame (ORF) sequences of MyoD1 and MyoD2 in S. lalandi encoded 298 and 263 amino acids possessing three common characteristic domains, respectively, containing a myogenic basic domain, a bHLH domain, and a ser-rich region (helix III). S. lalandi MyoDs shared the highest identity with the MyoDs of S. dumerili. MyoDs are highly expressed in white muscle (P < 0.05) in S. lalandi. The expression level of MyoD1 mRNA was higher than that of MyoD2 mRNA during embryonic and early developmental stages, indicating that the two MyoD isoforms may have different roles in muscle formation. Moreover, the mRNA expression of MyoDs in the brain, pituitary, liver and muscle of endocrine growth axis were analyzed in the various sizes and ages stages. The expression levels of MyoDs in the different sizes and ages of S. lalandi showed that expression of both these genes was particularly high in 400-g fish and 2-year-old fish (P < 0.05). Moreover, the increases in the mRNA expression and plasma levels of growth hormone (GH) and insulin-like growth factor (IGF-I) were accompanied by an increase in mRNA expression of MyoDs, indicating the roles of GH and IGF-I in muscle development and growth of S. lalandi. Overall, the expression profiles of genes associated with muscle development are the first step taken towards deciphering fast growth mechanism in this important Seriola fish.

Activities of Energy Metabolism Enzymes in Atlantic Salmon Salmo salar L. Smolts and Parr Grown under Different Light Regimens

Activities of enzymes of energy and carbohydrate metabolism in muscles and the liver were studied in Atlantic salmon Salmo salar L. smolts and parr grown under continuous or natural lighting and different feeding regimens in autumn followed by a short photoperiod in winter. Enzyme activities were found to differ between test and control salmon groups and between parr and smolts sampled at the end of the winter period. Smolts grown under continuous lighting and round-the-clock feeding differed from other groups by having higher cytochrome c oxidase (COX) activity and lower aldolase activity in muscles. Differences in aerobic metabolism in muscles between parr and smolts were found to be the same in all experimental groups, COX and aldolase activities being relatively higher in smolts. The pattern of changes in enzyme activities in the liver from parr to smolts differed between different experimental groups. Based on the results, the photoperiod was assumed to affect the activities of energy metabolism enzymes in salmon juveniles and may eventually affect the completion of smoltification.

Dietary Leucine Supplementation Improves Muscle Fiber Growth and Development by Activating AMPK/Sirt1 Pathway in Blunt Snout Bream (Megalobrama amblycephala)

This research is aimed at evaluating the effects of leucine supplementation on muscle fibers growth and development of blunt snout bream through a feeding trial and a primary muscle cells treatment. An 8-week trial with diets containing 1.61% leucine (LL) or 2.15% leucine (HL) was conducted in blunt snout bream (mean initial weight = 56.56 ± 0.83 g). Results demonstrated that the specific gain rate and the condition factor of fish in the HL group were the highest. The essential amino acids content of fish fed HL diets was significantly higher than that fed LL diets. The texture (hardness, springiness, resilience, and chewiness), the small-sized fiber ratio, fibers density, and sarcomere lengths in fish all obtained the highest in the HL group. Additionally, the proteins expression related with the activation of the AMPK pathway (p-Ampk, Ampk, p-Ampk/Ampk, and Sirt1) and the expression of genes (myogenin (myog), myogenic regulatory factor 4 (mrf4) and myoblast determination protein (myod), and protein (Pax7) related to muscle fiber formation were significantly upregulated with increasing level of dietary leucine. In vitro, the muscle cells were treated with 0, 40 and 160 mg/L leucine for 24 h. The results showed that treated with 40 mg/L leucine significantly raised the protein expressions of BCKDHA, Ampk, p-Ampk, p-Ampk/Ampk, Sirt1, and Pax7 and the gene expressions of myog, mrf4, and myogenic factor 5 (myf5) in muscle cells. In summary, leucine supplementation promoted muscle fibers growth and development, which may be related to the activation of BCKDH and AMPK.

The Effect of Continuous Light on Growth and Muscle-Specific Gene Expression in Atlantic Salmon (Salmo salar L.) Yearlings

Photoperiod is associated to phenotypic plasticity of somatic growth in several teleost species, however, the molecular mechanisms underlying this phenomenon are currently unknown. The effect of a continuous lighting (LD 24:0), compared with the usual hatchery lighting (HL) regime, on the growth rate and gene expression of myogenic regulatory factors (MRFs: MyoD1 paralogs, Myf5, and MyoG) myosin heavy chain (MyHC), and MSTN paralogs in the white muscles of hatchery-reared Atlantic salmon yearlings was evaluated over a 6-month period (May–October). The levels of gene expression were determined using real-time PCR. Continuous lighting was shown to have a positive effect on weight gain. MyHC, MyoD1c, MyoD1b, and MSTN1a/b mRNA expression was influenced by the light regime applied. In all the studied groups, a significant positive correlation was observed between the expression levels of MRFs and MSTN paralogs throughout the experiment. The study demonstrated seasonal patterns regarding the simultaneous expression of several MRFs. MyoD1a, MyoG, and MyHC mRNA expression levels were elevated in the mid-October, but MyoD1b/c, and Myf5 mRNA levels decreased by the end of this month. In general, the findings showed that constant lighting affected the regulatory mechanisms of muscle growth processes in salmon.

Muscle-specific gene expression and metabolic enzyme activities in Atlantic salmon Salmo salar L. fry reared under different photoperiod regimes

This study was conducted to characterise the muscle-specific gene expression, energy metabolism level and growth rates of Atlantic salmon Salmo salar L. reared under different photoperiod regimes. The effects of two photoperiod regimes - LD 16:8 (16 h light:8 h dark) and LD 24:0 (24 h light:0 h dark) over a period of 3 months (August to October) on growth, energy metabolism enzyme activities (cytochrome c oxidase, COX; lactate dehydrogenase, LDH; and aldolase) and the gene expression levels of myogenic regulatory factors (MRFs - MyoD1 paralogues (MyoD1a, MyoD1b, MyoD1c), Myf5, MyoG), myostatin paralogues (MSTN-1a, MSTN-1b, MSTN-2a) and the fast skeletal myosin heavy chain (MyHC) in the muscles of Atlantic salmon underyearling fry (0+) were investigated. The experiment was conducted in a fish hatchery with natural variations in water temperature. The results were compared with those obtained in salmon reared under the lighting conditions of a fish hatchery (HL, hatchery lighting). The results revealed that the fry reared under constant light (LD 24:0) grew faster and were bigger at the end of the experiment. Fishes reared within the photoperiod regime LD 16:8 had a lower growth rate. COX activity was lower in fish under the LD 16:8 regime compared with the LD 24:0 group. The LDH and aldolase enzyme activities were higher in the group with constant light in comparison to control in the beginning of September. The expression level for all of the genes studied variated during the duration of the experiment, and MyHC, MyoG, MyoD1a and Myf5 expression depended on the light regime as well. The more noticeable changes in gene expression occurred in October. The MyHC and MyoG mRNA levels increased, accompanied by MyD1c gene expression, in both groups that had additional lighting (LD 16:8 and LD24:0) at the beginning of October and were higher than the HL group. In the HL group, the elevation of MyHC and MyoG mRNA was gradual during October, but there was a sharp increase in Myf5 expression at the beginning of October. MyoD1 paralogues differently expressed during the experiment. The MyoD1a mRNA level was elevated at the end of October along with MyHC and MyoG expression, but MyoD1b and MyoD1c mRNA levels decreased along with Myf5 gene expression. The expression of MSTN paralogues were elevated with increases in MyHC and MRFs transcripts. These findings show that constant light has a positive effect on the growth rate of salmon, affecting the aerobic and anaerobic capacity in their muscles. The alterations in muscle-specific gene expression between the groups with different light indicated that the mechanisms for regulating muscle growth processes in fish depend on photoperiod duration.

Transcriptional shifts during juvenile Coho salmon (Oncorhynchus kisutch) life stage changes in freshwater and early marine environments

There is a paucity of information on the physiological changes that occur over the course of salmon early marine migration. Here we aim to provide insight on juvenile Coho salmon (Oncorhynchus kisutch) physiology using the changes in gene expression (cGRASP 44K microarray) of four tissues (brain, gill, muscle, and liver) across the parr to smolt transition in freshwater and through the first eight months of ocean residence. We also examined transcriptome changes with body size as a covariate. The strongest shift in the transcriptome for brain, gill, and muscle occurred between summer and fall in the ocean, representing physiological changes that we speculate may be associated with migration preparation to feeding areas. Metabolic processes in the liver were positively associated with body length, generally consistent with enhanced feeding opportunities. However, a notable exception to this metabolic pattern was for spring post-smolts sampled soon after entry into the ocean, which showed a pattern of gene expression more likely associated with depressed feeding or recent fasting. Overall, this study has revealed life stages that may be the most critical developmentally (fall post-smolt) and for survival (spring post-smolt) in the early marine environment. These life stages may warrant further investigation.