Cellular Mechanisms of Post-Embryonic Muscle Growth in Aquaculture Species

Combinatorial metabolomic and transcriptomic analysis of muscle growth in hybrid striped bass (female white bass Morone chrysops x male striped bass M. saxatilis)

BACKGROUND

Understanding growth regulatory pathways is important in aquaculture, fisheries, and vertebrate physiology generally. Machine learning pattern recognition and sensitivity analysis were employed to examine metabolomic small molecule profiles and transcriptomic gene expression data generated from liver and white skeletal muscle of hybrid striped bass (white bass Morone chrysops x striped bass M. saxatilis) representative of the top and bottom 10 % by body size of a production cohort.

RESULTS

Larger fish (good-growth) had significantly greater weight, total length, hepatosomatic index, and specific growth rate compared to smaller fish (poor-growth) and also had significantly more muscle fibers of smaller diameter (≤ 20 µm diameter), indicating active hyperplasia. Differences in metabolomic pathways included enhanced energetics (glycolysis, citric acid cycle) and amino acid metabolism in good-growth fish, and enhanced stress, muscle inflammation (cortisol, eicosanoids) and dysfunctional liver cholesterol metabolism in poor-growth fish. The majority of gene transcripts identified as differentially expressed between groups were down-regulated in good-growth fish. Several molecules associated with important growth-regulatory pathways were up-regulated in muscle of fish that grew poorly: growth factors including agt and agtr2 (angiotensins), nicotinic acid (which stimulates growth hormone production), gadd45b, rgl1, zfp36, cebpb, and hmgb1; insulin-like growth factor signaling (igfbp1 and igf1); cytokine signaling (socs3, cxcr4); cell signaling (rgs13, rundc3a), and differentiation (rhou, mmp17, cd22, msi1); mitochondrial uncoupling proteins (ucp3, ucp2); and regulators of lipid metabolism (apoa1, ldlr). Growth factors pttg1, egfr, myc, notch1, and sirt1 were notably up-regulated in muscle of good-growing fish.

CONCLUSION

A combinatorial pathway analysis using metabolomic and transcriptomic data collectively suggested promotion of cell signaling, proliferation, and differentiation in muscle of good-growth fish, whereas muscle inflammation and apoptosis was observed in poor-growth fish, along with elevated cortisol (an anti-inflammatory hormone), perhaps related to muscle wasting, hypertrophy, and inferior growth. These findings provide important biomarkers and mechanisms by which growth is regulated in fishes and other vertebrates as well.

Unveiling the emerging role of curcumin to alleviate ochratoxin A-induced muscle toxicity in grass carp (Ctenopharyngodon idella): in vitro and in vivo studies

BACKGROUND

Ochratoxin A (OTA), a globally abundant and extremely hazardous pollutant, is a significant source of contamination in aquafeeds and is responsible for severe food pollution. The developmental toxicity of OTA and the potential relieving strategy of natural products remain unclear. This study screened the substance curcumin (Cur), which had the best effect in alleviating OTA inhibition of myoblast proliferation, from 96 natural products and investigated its effect and mechanism in reducing OTA myotoxicity in vivo and in vitro.

METHODS

A total of 720 healthy juvenile grass carp, with an initial average body weight of 11.06 ± 0.05 g, were randomly assigned into 4 groups: the control group (without OTA and Cur), 1.2 mg/kg OTA group, 400 mg/kg Cur group, and 1.2 mg/kg OTA + 400 mg/kg Cur group. Each treatment consisted of 3 replicates (180 fish) for 60 d.

RESULTS

Firstly, we cultured, purified, and identified myoblasts using the tissue block culture method. Through preliminary screening and re-screening of 96 substances, we examined cell proliferation-related indicators such as cell viability and ultimately found that Cur had the best effect. Secondly, Cur could alleviate OTA-inhibited myoblast differentiation and myofibrillar development-related proteins (MyoG and MYHC) in vivo and in vitro and improve the growth performance of grass carp. Then, Cur could also promote the expression of OTA-inhibited protein synthesis-related proteins (S6K1 and TOR), which was related to the activation of the AKT/TOR signaling pathway. Finally, Cur could downregulate the expression of OTA-enhanced protein degradation-related genes (murf1, foxo3a, and ub), which was related to the inhibition of the FoxO3a signaling pathway.

CONCLUSIONS

In summary, our data demonstrated the effectiveness of Cur in alleviating OTA myotoxicity in vivo and in vitro. This study confirms the rapidity, feasibility, and effectiveness of establishing a natural product screening method targeting myoblasts to alleviate fungal toxin toxicity.

Pikeperch muscle tissues: a comparative study of structure, enzymes, genes, and proteins in wild and farmed fish

Pikeperch (Sander lucioperca) is a freshwater species and an internationally highly demanded fish in aquaculture. Despite intensive research efforts on this species, fundamental knowledge of skeletal muscle biology and structural characteristics is missing. Therefore, we conducted a comprehensive analysis of skeletal muscle parameters in adult pikeperch from two different origins, wild-caught specimens from a lake and those reared in a recirculating aquaculture system. The analyses comprised the biochemical characteristics (nucleic acid, protein content), enzyme activities (creatine kinase, lactate dehydrogenase, NADP-dependent isocitrate dehydrogenase), muscle-specific gene and protein expression (related to myofibre formation, regeneration and permanent growth, muscle structure), and muscle fibre structure. The findings reveal distinct differences between the skeletal muscle of wild and farmed pikeperch. Specifically, nucleic acid content, enzyme activity, and protein expression varied significantly. The higher enzyme activity observed in wild pikeperch suggests greater metabolically activity in their muscles. Conversely, farmed pikeperch indicated a potential for pronounced muscle growth. As the data on pikeperch skeletal muscle characteristics is sparse, the purpose of our study is to gain fundamental insights into the characteristics of adult pikeperch muscle. The presented data serve as a foundation for further research on percids' muscle biology and have the potential to contribute to advancements and adaptations in aquaculture practices.

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.

Growth, survival, and myogenic gene expression in the post-larvae of Colossoma macropomum provisioned with Artemia nauplii

Artemia nauplii are widely used as fish larvae feed due to its beneficial nutritional characteristics for larval development; however, efficient feeding strategies are needed to balance its high costs. Therefore, we evaluated the effects of different densities of Artemia nauplii (100, 250, 500, 750, and 1000 nauplii/post-larvae) on the growth, survival, water quality, and myogenic gene expression of tambaqui (Colossoma macropomum) post-larvae cultivated in a recirculating aquaculture system. After 2 weeks of trial, there was a significant decrease in dissolved oxygen concentration with the increase in nauplii density, but it did not interfere with larval performance and survival. In the first week, larvae fed with fewer than 500 nauplii/post-larvae presented slower growth, while in the second week, larvae fed with 1000 nauplii/post-larvae had the highest final weight and length. Regression analysis suggests that the optimum feeding density of Artemia nauplii during the first week is 411 nauplii/post-larvae, while for the second week, the growth increased proportionally to the feeding densities. The relative expression of the myod, myog, and mstn genes was higher in larvae fed with fewer than 500 nauplii/post-larvae. Although low-growing larvae showed increased expression of myod and myog genes, responsible for muscle hyperplasia and hypertrophy, respectively, mstn expression may have played a significant inhibitory role in larval development. Further research is needed to better determine the effects of the live food on the zootechnical performance and the expression of the myogenic genes in the initial phase of the life cycle of the tambaqui post-larvae.

Muscle Fiber Characteristics and Transcriptome Analysis in Slow- and Fast-Growing Megalobrama amblycephala

Growth is an important trait in aquaculture that is influenced by various factors, among which genetic regulation plays a crucial role. Megalobrama amblycephala, one of the most important freshwater species in China, exhibits wide variations in body mass among individuals of the same age within the same pool. But the molecular mechanisms underlying wide variation in body mass remain unclear. Here, we performed muscle histological and transcriptome analysis of muscle tissues from Fast-Growing (FG) and Slow-Growing (SG) M. amblycephala at the age of 4 months old (4 mo) and 10 months old (10 mo) to elucidate its muscle development and growth mechanism. The muscle histological analysis showed smaller diameter and higher total number of muscle fibers in FG compared to SG at 4 mo, while larger diameter and total number of muscle fibers were detected in FG at 10 mo. The transcriptome analysis of muscle tissue detected 1171 differentially expressed genes (DEGs) between FG and SG at 4 mo, and 718 DEGs between FG and SG at 10 mo. Furthermore, 44 DEGs were consistently up-regulated in FG at both 4 mo and 10 mo. Up-regulated DEGs in FG at 4 mo were mainly enriched in the pathways related to cell proliferation, while down-regulated DEGs were significantly enriched in cell fusion and muscle contraction. Up-regulated DEGs in FG at 10 mo were mainly enriched in the pathways related to cell proliferation and protein synthesis. Therefore, these results provide novel insights into the molecular mechanism of M. amblycephala muscle growth at different stages, and will be of great guiding significance to promote the fast growth of M. amblycephala.

Single nucleotide polymorphisms in the MRFs gene family associated with growth in Nile tilapia

BACKGROUND

Muscle occupies most of the fish body, promoting the proliferation of fish muscle fibers can facilitate rapid growth and increase the body weight of fish. Some studiesSeveral previous suggest that Myogenic regulatory factors (MRFs) play an important role in the growth of fish.

OBJECTIVE

To investigate the association between the polymorphism of MRFs gene family and growth traits in Nile tilapia (Oreochromis niloticus), get more molecular markers for growth.

METHODS

Amplified the Nile tilapia MRFs family gene, including Myogenic determination 1 (Myod1), Myogenic determination 2 (Myod2), Myogenin (Myog), Myogenic factor 5 (Myf5), and Myogenic factor 6 (Myf6), single nucleotide polymorphism (SNP) were screened by Sanger sequencing.

RESULTS

A total of 16 SNP loci were screened, including six for Myf5, six for Myf6, one for Myog, one for Myod1 and two for Myod2. The growth traits were analyzed in relation to these 16 SNP loci, and the results indicated significant associations between all 16 SNP loci and the growth traits (P < 0.05). The linkage disequilibrium analysis revealed that D1 and D2 diplotypes of Myf5 gene, E1, E2, E3 and E4 of Myf6 gene, and F1 diplotype of Myod2 gene were significantly associated with superior growth traits.

CONCLUSION

There were 6, 6, 1, 1 and 2 growth-related molecular markers in Myf5, Myf6, Myog, Myod1 and Myod2 genes, respectively, which could be applied to the breeding of Nile tilapia.

Assessment of black soldier fly (Hermetia illucens) larvae meal as a potential substitute for soybean meal on growth performance and flesh quality of grass carp Ctenopharyngodon idellus

A 90-day feeding trial was conducted to assess the effects of black soldier fly larvae meal (BSFLM) as a replacement for soybean meal (SM) on growth performance and flesh quality of grass carp. A total of 420 grass carp (299.93 ± 0.85 g) were randomly divided into 7 groups (triplicate) and fed 7 diets with SM substitution of 0% (SM, control), 15% (BSFLM15), 30% (BSFLM30), 45% (BSFLM45), 60% (BSFLM60), 75% (BSFLM75) and 100% (BSFLM100) by BSFLM. The growth performance of grass carp in the BSFLM75 and BSFLM100 groups were significantly lower compared to other groups (P < 0.05). The mid-gut villus height was the lowest in the BSFLM100 group (P < 0.05). Muscle nutritional value was improved due to increased DHA (docosahexaenoic acid), EPA (eicosapentaenoic acid), total HUFA (highly unsaturated fatty acids) and glycine levels, and reached the optimum in the BSFLM100 group (P < 0.05). According to the results of principal component analysis and weight analysis of muscle texture and body color, all the BSFLM diets except BSFLM15 could improve muscle texture and body color and reached the optimum level in the BSFLM100 group. Muscle drip loss and hypoxanthine content were the lowest and muscle antioxidant capacity was the highest in the BSFLM75 group, and water- and salt-soluble protein contents reached the optimum level in the BSFLM60 group (P < 0.05). Dietary BSFLM significantly reduced muscle fiber area and diameter, and increased muscle fiber density and the proportion of small fiber (diameter <20 μm) (P < 0.05). Additionally, sarcomere lengths in the BSFLM75 and BSFLM100 groups were significantly higher than that in the SM group (P < 0.05). The mRNA relative expression levels of MyoD, Myf5, MyHC and FGF6b were remarkably up-regulated at an appropriate dietary BSFLM level (P < 0.05). In conclusion, BSFLM could replace up to 60% SM without an adverse effect on growth performance and improve the flesh quality of grass carp. The optimum levels of dietary BSFLM were 71.0 and 69.1 g/kg diet based on the final body weight and feed conversion ratio. The flesh quality was optimal when dietary SM was completely replaced with BSFLM (227 g/kg diet).

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.

Rearing Environment during the Endogenous Feeding Stage of Acipenser baerii

The aim of this study was to evaluate behaviour, growth, lipid composition, muscle development, and stress status of Siberian sturgeon larvae reared with two types of substrate: Bioballs1 (BB1) and Bioballs2 (BB2), when compared to no substrate (CTR). Sampling points were: hatching (T0), schooling (T1), and yolk-sac full absorption (T2). BB1 larvae were less active and showed no schooling behaviour. At T1 and at T2, BB1 larvae showed a significantly higher weight and total length than larvae reared in either CTR or BB2 (p < 0.05). The lipid content of larvae decreased over time, with little relevant differences between groups. At T2, total muscle area, slow muscle area and fast muscle area were significantly higher in larvae reared in BB1 (p < 0.05). No significant differences in muscle proliferation were found between groups. Real Time PCR was used for evaluating the relative expression of a pool of genes: myod, myog, mrf4, igf2, hsp70, hsp90a, hsp90b, and glut2. The expression of these genes did not seem to be much affected by the type of rearing substrate, except for myog and hsp70 at T1, which was greater in BB2 larvae. Our data suggest that the presence of a substrate during this developmental period seems to have positive effects but further studies would be necessary during the exogenous feeding stage.

Coding and Noncoding Genes Involved in Atrophy and Compensatory Muscle Growth in Nile Tilapia

Improvements in growth-related traits reduce fish time and production costs to reach market size. Feed deprivation and refeeding cycles have been introduced to maximize aquaculture profits through compensatory growth. However, the molecular compensatory growth signature is still uncertain in Nile tilapia. In this study, fish were subjected to two weeks of fasting followed by two weeks of refeeding. The growth curve in refed tilapia was suggestive of a partial compensatory response. Transcriptome profiling of starved and refed fish was conducted to identify genes regulating muscle atrophy and compensatory growth. Pairwise comparisons revealed 5009 and 478 differentially expressed (differential) transcripts during muscle atrophy and recovery, respectively. Muscle atrophy appears to be mediated by the ubiquitin-proteasome and autophagy/lysosome systems. Autophagy-related 2A, F-box and WD repeat domain containing 7, F-box only protein 32, miR-137, and miR-153 showed exceptional high expression suggesting them as master regulators of muscle atrophy. On the other hand, the muscle compensatory growth response appears to be mediated by the continuous stimulation of muscle hypertrophy which exceeded normal levels found in control fish. For instance, genes promoting ribosome biogenesis or enhancing the efficiency of translational machinery were upregulated in compensatory muscle growth. Additionally, myogenic microRNAs (e.g., miR-1 and miR-206), and hypertrophy-associated microRNAs (e.g., miR-27a-3p, miR-29c, and miR-29c) were reciprocally expressed to favor hypertrophy during muscle recovery. Overall, the present study provided insights into the molecular mechanisms regulating muscle mass in fish. The study pinpoints extensive growth-related gene networks that could be used to inform breeding programs and also serve as valuable genomic resources for future mechanistic studies.

Dietary Supplementation With Hydroxyproline Enhances Growth Performance, Collagen Synthesis and Muscle Quality of Carassius auratus Triploid

An eight-week experiment was undertaken to examine the effect of dietary hydroxyproline (Hyp) supplementation on growth performance, collagen synthesis, muscle quality of an improved triploid crucian carp (Carassius auratus Triploid) (ITCC). Six isonitrogenous (340 g/kg diet), isolipidic (60 g/kg diet) and isocaloric (17.80 MJ/kg diet) diets were formulated containing a certain amount of Hyp: 0.09% (the control group), 0.39, 0.76, 1.14, 1.53 and 1.90%. Each diet was randomly assigned to three tanks and each group was fed two times daily until apparent satiation. The results showed that growth performance and feed utilization of ITCC were significantly improved with the dietary Hyp level was increased from 0.09 to 0.76%. Crude protein, threonine and arginine content in the dorsal muscle in 0.76% hydroxyproline group were significantly higher than those in basic diet group (p < 0.05). The muscle textural characteristics increased remarkably with the amount of Hyp in the diet rising from 0.09 to 1.53% (p < 0.05). Meanwhile, the contents of type I collagen (Col I) and Pyridinium crosslink (PYD) in the muscle of fish were significantly increased by dietary Hyp (p < 0.05). The muscle fiber diameter and density of the fish were significantly increased when fed with 0.76% Hyp (p < 0.05). Furthermore, dietary supplementation with an appropriate concentration of Hyp substantially increased the expression of genes involved in collagen synthesis (col1a1, col1a2, p4hα1, p4hβ, smad4, smad5, smad9, and tgf-β) and muscle growth (igf-1, tor, myod, myf5, and myhc) (p < 0.05). In conclusion, dietary supplementation of Hyp can enhance fish growth performance, collagen production, muscle textural characteristics and muscle growth of ITCC. According to the SGR broken-line analysis, the recommended supplementation level of Hyp was 0.74% in the diet for ITCC, corresponding to 2.2% of dietary protein.

The Interaction of Dried Distillers Grains With Solubles (DDGS) Type and Level on Growth Performance, Health, Texture, and Muscle-Related Gene Expression in Grass Carp (Ctenopharyngodon idellus)

The aim of this study was to estimate the possible synergetic effects of the two levels of dietary dried distillers grains with solubles (DDGS) from different sources (US-imported and native) on the growth, health status, muscle texture, and muscle growth-related gene expression of juvenile grass carp. Four treatments of fish were fed with 4 isonitrogenous diets, namely, native DDGS20, native DDGS30, US-imported DDGS20, and US-imported DDGS30 for 60 days. The US-imported DDGS30 group showed the better growth and feed efficiency. Additionally, we observed a significant increase in hepatopancreatic total antioxidant capacity (T-AOC) and superoxide dismutase (SOD) in native DDGS groups. Moreover, raw muscle collagen increases considerably in the US-imported DDGS30 compared with the native DDGS30 group. In comparison with the native DDGS groups, the US-imported DDGS groups showed significantly decrease in all textural properties and fiber density, while increased fiber diameter. Dietary native DDGS inclusion significantly showed the upregulation of myog, myhc, and fgf6a expression in muscle, while the downregulation of the expression of myod and myf5. Overall, US-imported DDGS30 had a beneficial influence on growth via regulating genes involved in myogenesis and hypertrophy, the formation of collagen, but had negative impacts on antioxidant capacity and cooked muscle texture.

Diallel Cross Application and Histomolecular Characterization: An Attempt to Develop Reference Stock of Labeo ariza

The objective of the present study was to evaluate the growth performance and genetic variation in diallel crosses of Ariza labeo (Labeo ariza) originating from three geographically separated rivers (Atrai, Jamuna and Kangsha) in Bangladesh. Intra (G1K♀K♂, G2J♀J♂, and G3A♀A♂) and inter (G4K♀A♂, G5K♀J♂, G6A♀K♂, G7A♀J♂, G8J♀K♂, and G9J♀A♂) stocks were produced following diallel cross (sex ratio—1:1 and n = 48; 16 from each river). Reproductive and growth performance, muscle cellularity and genetic variation following genotyping of eight microsatellite markers (Lr1, Lr2, Lr3, Lr22, Lr24, Lr27, Lr28 and Lr29) and analysis of all crossbreeds was performed. The fertilization (95% ± 2.11%), hatching (88% ± 1.03%), and survival rates (82% ± 1.88%) of G4K♀A♂ were higher compared to other groups. With respect to length and weight gains (2.67 ± 0.4 cm and 3.39 ± 0.2 g), SGR (3.23% ± 0.20%), and heterosis (8.87% and 24.74%) G4K♀A♂ was the superior group. A higher number of hyperplastic muscle fibers, mean number of alleles (2.75) and mean observed heterozygosity (0.417) from G4K♀A♂ could be interpreted to mean that G4K♀A♂ comprise better performance efficiency compared to others and are considered for continuing the L. ariza stock improvement program.

An insight on the impact of teleost whole genome duplication on the regulation of the molecular networks controlling skeletal muscle growth

Fish muscle growth is a complex process regulated by multiple pathways, resulting on the net accumulation of proteins and the activation of myogenic progenitor cells. Around 350–320 million years ago, teleost fish went through a specific whole genome duplication (WGD) that expanded the existent gene repertoire. Duplicated genes can be retained by different molecular mechanisms such as subfunctionalization, neofunctionalization or redundancy, each one with different functional implications. While the great majority of ohnolog genes have been identified in the teleost genomes, the effect of gene duplication in the fish physiology is still not well characterized. In the present study we studied the effect of WGD on the transcription of the duplicated components controlling muscle growth. We compared the expression of lineage-specific ohnologs related to myogenesis and protein balance in the fast-skeletal muscle of pacus (Piaractus mesopotamicus—Ostariophysi) and Nile tilapias (Oreochromis niloticus—Acanthopterygii) fasted for 4 days and refed for 3 days. We studied the expression of 20 ohnologs and found that in the great majority of cases, duplicated genes had similar expression profiles in response to fasting and refeeding, indicating that their functions during growth have been conserved during the period after the WGD. Our results suggest that redundancy might play a more important role in the retention of ohnologs of regulatory pathways than initially thought. Also, comparison to non-duplicated orthologs showed that it might not be uncommon for the duplicated genes to gain or loss new regulatory elements simultaneously. Overall, several of duplicated ohnologs have similar transcription profiles in response to pro-growth signals suggesting that evolution tends to conserve ohnolog regulation during muscle development and that in the majority of ohnologs related to muscle growth their functions might be very similar.

Dietary Selenium Promotes Somatic Growth of Rainbow Trout (Oncorhynchus mykiss) by Accelerating the Hypertrophic Growth of White Muscle

As a nutritionally essential trace element, selenium (Se) is crucial for fish growth. However, the underlying mechanisms remain unclear. Fish somatic growth relies on the white muscle growth. This study aimed to explore the effects and underlying mechanisms of Se on fish white muscle growth using a juvenile rainbow trout (Oncorhynchus mykiss) model. Fish were fed a basal diet unsupplemented or supplemented with selenium yeast at nutritional dietary Se levels (2 and 4 mg/kg Se, respectively) for 30 days. Results showed that dietary Se supplementation significantly enhanced trout somatic growth. Histological and molecular analysis of trout white muscle tissues at the vent level showed that dietary Se supplementation elevated the total cross-sectional area of white muscle, mean diameter of white muscle fibers, protein content, nuclei number, and DNA content of individual muscle fiber, and suppressed the activities of calpain system and ubiquitin-proteasome pathway. Overall, this study demonstrated that dietary Se within the nutritional range inhibits calpain- and ubiquitin-mediated protein degradation and promotes the fusion of myoblasts into the existed muscle fibers to promote the hypertrophic growth of white muscle, thereby accelerating the somatic growth of rainbow trout. Our results provide a mechanistic insight into the regulatory role of Se in fish growth.

Adult neurogenesis in the central nervous system of teleost fish: from stem cells to function and evolution

Adult neurogenesis, the generation of functional neurons from adult neural stem cells in the central nervous system (CNS), is widespread, and perhaps universal, among vertebrates. This phenomenon is more pronounced in teleost fish than in any other vertebrate taxon. There are up to 100 neurogenic sites in the adult teleost brain. New cells, including neurons and glia, arise from neural stem cells harbored both in neurogenic niches and outside these niches (such as the ependymal layer and parenchyma in the spinal cord, respectively). At least some, but not all, of the stem cells are of astrocytic identity. Aging appears to lead to stem cell attrition in fish that exhibit determinate body growth but not in those with indeterminate growth. At least in some areas of the CNS, the activity of the neural stem cells results in additive neurogenesis or gliogenesis - tissue growth by net addition of cells. Mathematical and computational modeling has identified three factors to be crucial for sustained tissue growth and correct formation of CNS structures: symmetric stem cell division, cell death and cell drift due to population pressure. It is hypothesized that neurogenesis in the CNS is driven by continued growth of corresponding muscle fibers and sensory receptor cells in the periphery to ensure a constant ratio of peripheral versus central elements. This 'numerical matching hypothesis' can explain why neurogenesis has ceased in most parts of the adult CNS during the evolution of mammals, which show determinate growth.

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.

Dietary carbohydrates influence muscle texture of olive flounder Paralichthys olivaceus through impacting mitochondria function and metabolism of glycogen and protein

The present study was conducted to estimate the effects of dietary carbohydrates on muscle quality and the underlying mechanisms. Six isonitrogenous and isolipidic diets were formulated to contain graded levels of carbohydrates (0%, 8%, 12%, 16%, 20% and 24%, respectively). These diets were named as C0, C8, C12, C16, C20 and C24, respectively. After a 10-week feeding trial, results showed that the muscle pH, liquid holding capacity (LHC) and hardness were significantly decreased by the increasing dietary carbohydrate levels. Dietary carbohydrates significantly decreased the muscle fibre diameter, and the highest value was found in the C0 group. Accumulated glycogen and degenerated mitochondrial cristae were observed in the C24 group. Significantly higher contents of protein carbonyls were observed in the C20 group and C24 group (P < 0.05). There was a significant decrease of mtDNA copy number in the C24 group compared with that in the C0 and C8 groups. The AMP/ATP ratio in muscle decreased first and then increased with the increasing dietary carbohydrate levels. The dietary incorporation of carbohydrate significantly reduced the expression of opa1, pygm and genes involved in myogenesis (myf5 and myog). Meanwhile, proteolysis-related genes (murf-1, mafbx, capn2 and ctsl), pro-inflammatory cytokines (il-6 and tnf-α) and mstn were significantly up-regulated. In the C24 group, significant increase of phosphorylation of AMPK (Thr172), up-regulation of PGC-1α and GLUT4 were observed, while the phosphorylation level of S6 (Ser235/236) was significantly decreased. It was concluded that excessive dietary carbohydrate level (24%) had negative impacts on mitochondria function and promoted glycogen accumulation, and thereafter influenced the muscle quality of olive flounder. The activation of AMPK as well as the upregulation of PGC-1α and GLUT4 was the key mechanism.

Identifying the Related Genes of Muscle Growth and Exploring the Functions by Compensatory Growth in Mandarin Fish (Siniperca chuatsi)

How organisms display many different biochemical, physiological processes through genes expression and regulatory mechanisms affecting muscle growth is a central issue in growth and development. In Siniperca chuatsi, the growth-related genes and underlying relevant mechanisms are poorly understood, especially for difference of body sizes and compensatory growth performance. Muscle from 3-month old individuals of different sizes was used for transcriptome analysis. Results showed that 8,942 different expression genes (DEGs) were identified after calculating the RPKM. The DEGs involved in GH-IGF pathways, protein synthesis, ribosome synthesis and energy metabolisms, which were expressed significantly higher in small individuals (S) than large fish (L). In repletion feeding and compensatory growth experiments, eight more significant DEGs were used for further research (GHR2, IGFR1, 4ebp, Mhc, Mlc, Myf6, MyoD, troponin). When food was plentiful, eight genes participated in and promoted growth and muscle synthesis, respectively. Starvation can be shown to inhibit the expression of Mhc, Mlc and troponin, and high expression of GHR2, IGFR1, and 4ebp inhibited growth. Fasting promoted the metabolic actions of GHR2, IGFR1, and 4ebp rather than the growth-promoting actions. MyoD can sense and regulate the hunger, which also worked with Mhc and Mlc to accelerate the compensatory growth of S. chuatsi. This study is helpful to understand the regulation mechanisms of muscle growth-related genes. The elected genes will contribute to the selective breeding in future as candidate genes.

Chronic exposure to copper oxide nanoparticles causes muscle toxicity in adult zebrafish

Repeated deposition of copper oxide nanoparticles (CuO-NPs) into aquatic systems makes them a global threat since the NPs accumulate in various organs of the fish particularly skeletal muscle. In the present study, adult zebrafish were exposed to different concentrations of CuO-NPs (1 and 3 mg/L) for a period of 30 days. The status of functional markers (acetylcholinesterase, creatine kinase-MB, and lactate dehydrogenase) and oxidative stress markers (oxidants and antioxidants) were analyzed. The histological changes in muscle were studied followed by the immunohistochemistry expression for catalase. Further, the expression of myoD, myogenin, pax7, β-actin, and desmin was examined by semi-quantitative reverse transcriptase polymerase chain reaction. The results indicated that chronic exposure to CuO-NPs causes muscular damage as evidenced by elevated levels of functional markers. There was a significant increase in the oxidants with reduction in the antioxidant levels, implying that the antioxidant enzymes were unable to scavenge the free radicals induced by the CuO-NPs. The histopathological analysis showed degeneration and atrophy in the treated groups confirming muscle damage. The immunohistochemical catalase expression in the muscle was reduced in the treated groups further supporting the evidence that the antioxidant has suffered a decline. The altered gene expression indicates skeletal muscle damage due to the CuO-NPs exposure. Overall, the data suggest that chronic exposure to CuO-NPs caused muscular toxicity which may lead to muscle degeneration in adult zebrafish.

Skeletal Muscle and the Effects of Ammonia Toxicity in Fish, Mammalian, and Avian Species: A Comparative Review Based on Molecular Research

Typically, mammalian and avian models have been used to examine the effects of ammonia on skeletal muscle. Hyperammonemia causes sarcopenia or muscle wasting, in mammals and has been linked to sarcopenia in liver disease patients. Avian models of skeletal muscle have responded positively to hyperammonemia, differing from the mammalian response. Fish skeletal muscle has not been examined as extensively as mammalian and avian muscle. Fish skeletal muscle shares similarities with avian and mammalian muscle but has notable differences in growth, fiber distribution, and response to the environment. The wide array of body sizes and locomotion needs of fish also leads to greater diversity in muscle fiber distribution and growth between different fish species. The response of fish muscle to high levels of ammonia is important for aquaculture and quality food production but has not been extensively studied to date. Understanding the differences between fish, mammalian and avian species’ myogenic response to hyperammonemia could lead to new therapies for muscle wasting due to a greater understanding of the mechanisms behind skeletal muscle regulation and how ammonia effects these mechanisms. This paper provides an overview of fish skeletal muscle and ammonia excretion and toxicity in fish, as well as a comparison to avian and mammalian species.

Feeding Faba Beans (Vicia faba L.) Reduces Myocyte Metabolic Activity in Grass Carp (Ctenopharyngodon idellus)

In this study, we aimed to explore the effects of faba bean (Vicia faba L.) on the energy metabolism of grass carp (Ctenopharyngodon idellus). A total of 180 fish (∼2900 g) were randomly assigned to six tanks (2.5 × 2.5 × 1.2 m; 30 individuals per tank) and fed either faba bean (Vicia faba L.) or a commercial diet for 120 days (3% body weight, twice per day). The results showed that faba bean-fed grass carp (FBFG) had significantly lower growth and higher fat accumulation in the mesenteric adipose tissue and hepatopancreas than commercial diet-fed grass carp (CDFG). Compared with CDFG, FBFG exhibited no significant difference in proximate composition of the muscle; however, an obvious decrease in muscle fiber size and significantly higher hardness, chewiness, and gumminess were observed. Transcriptome results showed that a total of 197 genes were differentially regulated in the dorsal muscle. Down-regulated genes included four genes annotated with myocyte development and 12 transcripts annotated with components of myofibrils. In addition, the FBFG group exhibited significantly lower expression of genes associated with oxygen transport, the mitochondrial respiratory chain, and creatine metabolism, suggesting reduced energy availability in the muscle of the FBFG. Moreover, using western-blotting and enzyme assays, we found decreased protein levels in the mitochondrial electron transport respiratory chain and creatine metabolism activities, as well as increased expression of autophagy marker protein levels, in the muscle of FBFG. Overall, our results suggest that an abnormal energy distribution may exist in grass carps after feeding with faba bean, which is reflected by a mass of fat deposition in the adipose tissue and hepatopancreas and subdued metabolic activity in the muscle.

Anterior trunk muscle shows mix of axial and appendicular developmental patterns

BACKGROUND

Skeletal muscle in the trunk derives from the somites, paired segments of paraxial mesoderm. Whereas axial musculature develops within the somite, appendicular muscle develops following migration of muscle precursors into lateral plate mesoderm. The development of muscles bridging axial and appendicular systems appears mixed.

RESULTS

We examine development of three migratory muscle precursor-derived muscles in zebrafish: the sternohyoideus (SH), pectoral fin (PF), and posterior hypaxial (PHM) muscles. We show there is an anterior to posterior gradient to the developmental gene expression and maturation of these three muscles. SH muscle precursors exhibit a long delay between migration and differentiation, PF muscle precursors exhibit a moderate delay in differentiation, and PHM muscle precursors show virtually no delay between migration and differentiation. Using lineage tracing, we show that lateral plate contribution to the PHM muscle is minor, unlike its known extensive contribution to the PF muscle and absence in the ventral extension of axial musculature.

CONCLUSIONS

We propose that PHM development is intermediate between a migratory muscle mode and an axial muscle mode of development, wherein the PHM differentiates after a very short migration of its precursors and becomes more anterior primarily by elongation of differentiated muscle fibers.

The Developmental Phases of Zebrafish Myogenesis

The development and growth of vertebrate axial muscle have been studied for decades at both the descriptive and molecular level. The zebrafish has provided an attractive model system for investigating both muscle patterning and growth due to its simple axial musculature with spatially separated fibre types, which contrasts to complex muscle groups often deployed in amniotes. In recent years, new findings have reshaped previous concepts that define how final teleost muscle form is established and maintained. Here, we summarise recent findings in zebrafish embryonic myogenesis with a focus on fibre type specification, followed by an examination of the molecular mechanisms that control muscle growth with emphasis on the role of the dermomyotome-like external cell layer. We also consider these data sets in a comparative context to gain insight into the evolution of axial myogenic patterning systems within the vertebrate lineage.

Influence of feed ration size on somatic and muscle growth in landlocked dwarf and farmed Atlantic salmon Salmo salar

We examined the possible adaptation of the dwarf Bleke population of Atlantic salmon Salmo salar from Lake Byglandsfjord in southern Norway to limited food resources. The growth performance and muscle development in juvenile Bleke and farmed S. salar under satiated or restricted (50%) feeding were examined for 10 months, starting 3 weeks after first-feeding stage. Four-thousand fish were divided into four replicated groups and random samples of 16-40 fish per group were measured six times during the experiment. The two strains showed no significant difference in mean body mass when fed restricted ration, but the individual variation was considerably higher in the farmed fish. Both Bleke and farmed S. salar grew significantly faster when fed to satiation, but the farmed S. salar showed much higher gain in mass and were three times heavier (201.5 g vs 66.7 g) and possessed twice as many fast muscle fibres (179,682 vs 84,779) compared with landlocked S. salar after 10 months. Farmed fish fed full ration displayed both hypertrophic and hyperplasic muscle growth, while the increased growth in Bleke S. salar was entirely associated with a larger fibre diameter. The landlocked Bleke strain has apparently adapted to low food availability by minimising the metabolic costs of maintenance and growth through reduced dominance hierarchies and by an increase in average muscle fibre diameter relative to the ancestral condition.

Multiple transcription factors mediating the expressional regulation of myosin heavy chain gene involved in the indeterminate muscle growth of fish

Torafugu myosin heavy chain gene, MYH_M2528-1, is specifically expressed in neonatal slow and fast muscle fibers, suggesting its functional role in indeterminate muscle growth in fish. However, the transcriptional regulatory mechanisms of MYH_M2528-1 involved in indeterminate muscle growth in fish remained unknown. We previously isolated a 2100 bp 5'- flanking sequence of torafugu MYH_M2528-1 that showed sufficient promoter activity to allow specific gene expression in neonatal muscle fibers of zebrafish. Here, we examined the cis-regulatory mechanism of 2100 bp 5'-flanking region of torafugu MYH_M2528-1 using deletion-mutation analysis in zebrafish embryo. We discovered that myoblast determining factor (MyoD) binding elements play a key role and participate in the transcriptional regulation of MYH_M2528-1 expression in zebrafish embryos. We further discovered that paired box protein (Pax3) are required for promoting MYH_M2528-1 expression and myocyte enhancer factor-2 (MEF2) binding sites participate in the transcriptional regulation of MYH_M2528-1 expression in slow/fast skeletal muscles. Our study also confirmed that the nuclear factor of activated T-cell (NFAT) binding sites take part in the transcriptional regulation of MYH_M2528-1 expression in slow and fast muscles fiber in relation to indeterminate muscle growth. These results obviously confirmed that multiple cis-elements in the 5'-flanking region of MYH_M2528-1 function in the transcriptional regulation of its expression.

Ascorbic acid stimulates the in vitro myoblast proliferation and migration of pacu (Piaractus mesopotamicus)

The postembryonic growth of skeletal muscle in teleost fish involves myoblast proliferation, migration and differentiation, encompassing the main events of embryonic myogenesis. Ascorbic acid plays important cellular and biochemical roles as an antioxidant and contributes to the proper collagen biosynthesis necessary for the structure of connective and bone tissues. However, whether ascorbic acid can directly influence the mechanisms of fish myogenesis and skeletal muscle growth remains unclear. The aim of our work was to evaluate the effects of ascorbic acid supplementation on the in vitro myoblast proliferation and migration of pacu (Piaractus mesopotamicus). To provide insight into the potential antioxidant role of ascorbic acid, we also treated myoblasts in vitro with menadione, which is a powerful oxidant. Our results show that ascorbic acid-supplemented myoblasts exhibit increased proliferation and migration and are protected against the oxidative stress caused by menadione. In addition, ascorbic acid increased the activity of the antioxidant enzyme superoxide dismutase and the expression of myog and mtor, which are molecular markers related to skeletal muscle myogenesis and protein synthesis, respectively. This work reveals a direct influence of ascorbic acid on the mechanisms of pacu myogenesis and highlights the potential use of ascorbic acid for stimulating fish skeletal muscle growth.

Histological, transcriptomic and in vitro analysis reveal an intrinsic activated state of myogenic precursors in hyperplasic muscle of trout

BACKGROUND

The dramatic increase in myotomal muscle mass in post-hatching fish is related to their ability to lastingly produce new muscle fibres, a process termed hyperplasia. The molecular and cellular mechanisms underlying fish muscle hyperplasia largely remain unknown. In this study, we aimed to characterize intrinsic properties of myogenic cells originating from hyperplasic fish muscle. For this purpose, we compared in situ proliferation, in vitro cell behavior and transcriptomic profile of myogenic precursors originating from hyperplasic muscle of juvenile trout (JT) and from non-hyperplasic muscle of fasted juvenile trout (FJT) and adult trout (AT).

RESULTS

For the first time, we showed that myogenic precursors proliferate in hyperplasic muscle from JT as shown by in vivo BrdU labeling. This proliferative rate was very low in AT and FJT muscle. Transcriptiomic analysis revealed that myogenic cells from FJT and AT displayed close expression profiles with only 64 differentially expressed genes (BH corrected p-val < 0.001). In contrast, 2623 differentially expressed genes were found between myogenic cells from JT and from both FJT and AT. Functional categories related to translation, mitochondrial activity, cell cycle, and myogenic differentiation were inferred from genes up regulated in JT compared to AT and FJT myogenic cells. Conversely, Notch signaling pathway, that signs cell quiescence, was inferred from genes down regulated in JT compared to FJT and AT. In line with our transcriptomic data, in vitro JT myogenic precursors displayed higher proliferation and differentiation capacities than FJT and AT myogenic precursors.

CONCLUSIONS

The transcriptomic analysis and examination of cell behavior converge to support the view that myogenic cells extracted from hyperplastic muscle of juvenile trout are intrinsically more potent to form myofibres than myogenic cells extracted from non-hyperplasic muscle. The generation of gene expression profiles in myogenic cell extracted from muscle of juvenile trout may yield insights into the molecular and cellular mechanisms controlling hyperplasia and provides a useful list of potential molecular markers of hyperplasia.

Diet Affects Muscle Quality and Growth Traits of Grass Carp (Ctenopharyngodon idellus): A Comparison Between Grass and Artificial Feed

Fish muscle, the main edible parts with high protein level and low fat level, is consumed worldwide. Diet contributes greatly to fish growth performance and muscle quality. In order to elucidate the correlation between diet and muscle quality, the same batch of juvenile grass carp (Ctenopharyngodon idellus) were divided into two groups and fed with either grass (Lolium perenne, Euphrasia pectinata and Sorghum sudanense) or artificial feed, respectively. However, the different two diets didn't result in significant differences in all the detected water quality parameters (e.g., Tm, pH, DO, NH3/[Formula: see text]-N, [Formula: see text]-N, [Formula: see text], TN, TP, and TOC) between the two experimental groups. After a 4-month culture period, various indexes and expression of myogenic regulatory factor (MRFs) and their related genes were tested. The weight gain of the fish fed with artificial feed (AFG) was nearly 40% higher than the fish fed with grass (GFG). Significantly higher alkaline phosphatase, total cholestrol, high density cholestrol and total protein were detected in GFG as compared to AFG. GFG also showed increased hardness, resilience and shear force in texture profile analysis, with significantly bigger and compact muscle fibers in histologic slices. The fat accumulation was most serious in the abdomen muscle of AFG. Additionally, the expression levels of MyoG, MyoD, IGF-1, and MSTNs were higher, whereas Myf-5, MRF4, and IGF-2 were lower in most positional muscles of GFG as compared to AFG. Overall, these results suggested that feeding grass could promote muscle growth and development by stimulating muscle fiber hypertrophy, as well as significantly enhance the expression of CoL1As. Feeding C. idellus with grass could also improve flesh quality by improving muscle characteristics, enhancing the production of collagen, meanthile, reducing fat accumulation and moisture in muscle, but at the cost of a slower growth.

Global gene expression in muscle from fasted/refed trout reveals up-regulation of genes promoting myofibre hypertrophy but not myofibre production

BACKGROUND

Compensatory growth is a phase of rapid growth, greater than the growth rate of control animals, that occurs after a period of growth-stunting conditions. Fish show a capacity for compensatory growth after alleviation of dietary restriction, but the underlying cellular mechanisms are unknown. To learn more about the contribution of genes regulating hypertrophy (an increase in muscle fibre size) and hyperplasia (the generation of new muscle fibres) in the compensatory muscle growth response in fish, we used high-density microarray analysis to investigate the global gene expression in muscle of trout during a fasting-refeeding schedule and in muscle of control-fed trout displaying normal growth.

RESULTS

The compensatory muscle growth signature, as defined by genes up-regulated in muscles of refed trout compared with control-fed trout, showed enrichment in functional categories related to protein biosynthesis and maturation, such as RNA processing, ribonucleoprotein complex biogenesis, ribosome biogenesis, translation and protein folding. This signature was also enriched in chromatin-remodelling factors of the protein arginine N-methyl transferase family. Unexpectedly, functional categories related to cell division and DNA replication were not inferred from the molecular signature of compensatory muscle growth, and this signature contained virtually none of the genes previously reported to be up-regulated in hyperplastic growth zones of the late trout embryo myotome and to potentially be involved in production of new myofibres, notably genes encoding myogenic regulatory factors, transmembrane receptors essential for myoblast fusion or myofibrillar proteins predominant in nascent myofibres.

CONCLUSION

Genes promoting myofibre growth, but not myofibre formation, were up-regulated in muscles of refed trout compared with continually fed trout. This suggests that a compensatory muscle growth response, resulting from the stimulation of hypertrophy but not the stimulation of hyperplasia, occurs in trout after refeeding. The generation of a large set of genes up-regulated in muscle of refed trout may yield insights into the molecular and cellular mechanisms controlling skeletal muscle mass in teleost and serve as a useful list of potential molecular markers of muscle growth in fish.

Gene expression profiling of trout regenerating muscle reveals common transcriptional signatures with hyperplastic growth zones of the post-embryonic myotome

Background

Muscle fibre hyperplasia stops in most fish when they reach approximately 50 % of their maximum body length. However, new small-diameter muscle fibres can be produced de novo in aged fish after muscle injury. Given that virtually nothing is known regarding the transcriptional mechanisms that regulate regenerative myogenesis in adult fish, we explored the temporal changes in gene expression during trout muscle regeneration following mechanical crushing. Then, we compared the gene transcription profiles of regenerating muscle with the previously reported gene expression signature associated with muscle fibre hyperplasia.

Results

Using an Agilent-based microarray platform we conducted a time-course analysis of transcript expression in 29 month-old trout muscle before injury (time 0) and at the site of injury 1, 8, 16 and 30 days after lesions were made. We identified more than 7000 unique differentially expressed transcripts that segregated into four major clusters with distinct temporal profiles and functional categories. Functional categories related to response to wounding, response to oxidative stress, inflammatory processes and angiogenesis were inferred from the early up-regulated genes, while functions related to cell proliferation, extracellular matrix remodelling, muscle development and myofibrillogenesis were inferred from genes up-regulated 30 days post-lesion, when new small myofibres were visible at the site of injury. Remarkably, a large set of genes previously reported to be up-regulated in hyperplastic muscle growth areas was also found to be overexpressed at 30 days post-lesion, indicating that many features of the transcriptional program underlying muscle hyperplasia are reactivated when new myofibres are transiently produced during fish muscle regeneration.

Conclusion

The results of the present study demonstrate a coordinated expression of functionally related genes during muscle regeneration in fish. Furthermore, this study generated a useful list of novel genes associated with muscle regeneration that will allow further investigations on the genes, pathways or biological processes involved in muscle growth and regeneration in vertebrates.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-3160-x) contains supplementary material, which is available to authorized users.

On the Role of Neurogenesis and Neural Plasticity in the Evolution of Animal Personalities and Stress Coping Styles

Individual variation in how animals react to stress and environmental change has become a central topic in a wide range of biological disciplines, from evolutionary ecology to biomedicine. Such variation manifests phenotypically as correlated trait-clusters (referred to as coping styles, behavioral syndromes, shyness-boldness, or personality traits). Thresholds for switching from active coping (fight-flight) to inhibition and passive behavior when exposed to stress depend on experience and genetic factors. Comparative research has revealed a range of neuroendocrine-behavioral associations which are conserved throughout the vertebrate subphylum, including factors affecting perception, learning, and memory of stimuli and events. Here we review conserved aspects of the contribution of neurogenesis and other aspects of neural plasticity to stress coping. In teleost fish, brain cell proliferation and neurogenesis have received recent attention. This work reveals that brain cell proliferation and neurogenesis are associated with heritable variation in stress coping style, and they are also differentially affected by short- and long-term stress in a biphasic manner. Routine-dependent and inflexible behavior in proactive individuals is associated with limited neural plasticity. These evolutionarily conserved relationships hold the potential to illuminate the biological background for stress-related neurobiological disorders.

Transient up- and down-regulation of expression of myosin light chain 2 and myostatin mRNA mark the changes from stratified hyperplasia to muscle fiber hypertrophy in larvae of gilthead sea bream (Sparus aurata L.)

Hyperplasia and hypertrophy are the two mechanisms by which muscle develops and grows. We study these two mechanisms, during the early development of white muscle in Sparus aurata, by means of histology and the expression of structural and regulatory genes. A clear stage of stratified hyperplasia was identified early in the development of gilthead sea bream but ceased by 35 dph when hypertrophy took over. Mosaic recruitment of new white fibers began as soon as 60 dph. The genes mlc2a and mlc2b were expressed at various levels during the main phases of hyperplasia and hypertrophy. The genes myog and mlc2a were significantly up-regulated during the intensive stratified formation of new fibers and their expression was significantly correlated. Expression of mstn1 and igf1 increased at 35 dph, appeared to regulate the hyperplasia-to-hypertrophy transition, and may have stimulated the expression of mlc2a, mlc2b and col1a1 at the onset of mosaic hyperplasia. The up-regulation of mstn1 at transitional phases in muscle development indicates a dual regulatory role of myostatin in fish larval muscle growth.

Oncorhynchus mykiss pax7 sequence variations with comparative analyses against other teleost species

The paired box-7 (pax7) transcription factor expressed in satellite cells (SCs) is an essential regulator of skeletal muscle growth and regeneration in vertebrates including fish. Characterization of rainbow trout (Oncorhynchus mykiss) pax7 gene/s may offer novel insights into skeletal myogenesis by SCs in this indeterminate growth species. Further, evaluation of promoters for cis-regulatory regions may shed light on the evolutionary fate of the duplicated genes. Employing standard PCR, cloning and computational approach, we identified and report complete coding sequences of two pax7 paralogs of rainbow trout (rt); rtpax7α and rtpax7β. Both genes show significant identity in the nucleotide (97%) and the predicted amino acid (98%) sequences, and bear the characteristic paired domain (PD), octapeptide (OP) and homeodomain (HD) motifs. We further report several splice variants of each gene and nucleotide differences in coding sequence that predicts six putative amino acid changes between the two genes. Additionally, we noted a trinucleotide deletion in rtpax7β that results in putative serine elimination at the N-terminus and a single nucleotide polymorphism (SNP) in majority of the rtpax7β variants (6/10) that predicts an arginine substitution for a lysine. We also deciphered the genomic organization up to the first three exons and the upstream putative promoter regions of both genes. Comparative in silico analysis of both the trout pax7 promoters with that of zebrafish pax7 duplicates; zfpax7a and zfpax7b; predicts several important cis-elements/transcription factor binding sites (TFBS) in these teleost pax7 promoter regions.

Analysis of muscle fibre input dynamics using a myog:GFP transgenic trout model

The dramatic increase in myotomal muscle mass in teleosts appears to be related to their sustained ability to produce new fibres in the growing myotomal muscle. To describe muscle fibre input dynamics in trout (Oncorhynchus mykiss), we generated a stable transgenic line carrying green fluorescent protein (GFP) cDNA driven by the myogenin promoter. In this myog:GFP transgenic line, muscle cell recruitment is revealed by the appearance of fluorescent, small, nascent muscle fibres. The myog:GFP transgenic line displayed fibre formation patterns in the developing trout and showed that the production of new fluorescent myofibres (muscle hyperplasia) is prevalent in the juvenile stage but progressively decreases to eventually cease at approximately 18 months post-fertilisation. However, fluorescent, nascent myofibres were formed de novo in injured muscle of aged trout, indicating that the inhibition of myofibre formation associated with trout ageing cannot be attributed to the lack of recruitable myogenic cells but rather to changes in the myogenic cell microenvironment. Additionally, the myog:GFP transgenic line demonstrated that myofibre production persists during starvation.

Skeletal myogenesis in the zebrafish and its implications for muscle disease modelling

Current evidence indicates that post-embryonic muscle growth and regeneration in amniotes is mediated almost entirely by stem cells derived from muscle progenitor cells (MPCs), known as satellite cells. Exhaustion and impairment of satellite cell activity is involved in the severe muscle loss associated with degenerative muscle diseases such as Muscular Dystrophies and is the main cause of age-associated muscle wasting. Understanding the molecular and cellular basis of satellite cell function in muscle generation and regeneration (myogenesis) is critical to the broader goal of developing treatments that may ameliorate such conditions. Considerable knowledge exists regarding the embryonic stages of amniote myogenesis. Much less is known about how post-embryonic amniote myogenesis proceeds, how adult myogenesis relates to embryonic myogenesis on a cellular or genetic level. Of the studies focusing on post-embryonic amniote myogenesis, most are post-mortem and in vitro analyses, precluding the understanding of cellular behaviours and genetic mechanisms in an undisturbed in vivo setting. Zebrafish are optically clear throughout much of their post-embryonic development, facilitating their use in live imaging of cellular processes. Zebrafish also possess a compartment of MPCs, which appear similar to satellite cells and persist throughout the post-embryonic development of the fish, permitting their use in examining the contribution of these cells to muscle tissue growth and regeneration.

Early decrease in dietary protein:energy ratio by fat addition and ontogenetic changes in muscle growth mechanisms of rainbow trout: short- and long-term effects

As the understanding of the nutritional regulation of muscle growth mechanisms in fish is fragmentary, the present study aimed to (1) characterise ontogenetic changes in muscle growth-related genes in parallel to changes in muscle cellularity; (2) determine whether an early decrease in dietary protein:energy ratio by fat addition affects the muscle growth mechanisms of rainbow trout (Oncorhynchus mykiss) alevins; and (3) determine whether this early feeding of a high-fat (HF) diet to alevins had a long-term effect on muscle growth processes in juveniles fed a commercial diet. Developmental regulation of hyperplasia and hypertrophy was evidenced at the molecular (expression of myogenic regulatory factors, proliferating cell nuclear antigen and myosin heavy chains (MHC)) and cellular (number and diameter of white muscle fibres) levels. An early decrease in dietary protein:energy ratio by fat addition stimulated the body growth of alevins but led to a fatty phenotype, with accumulation of lipids in the anterior part, and less caudal muscle when compared at similar body weights, due to a decrease in both the white muscle hyperplasia and maximum hypertrophy of white muscle fibres. These HF diet-induced cellular changes were preceded by a very rapid down-regulation of the expression of fast-MHC. The present study also demonstrated that early dietary composition had a long-term effect on the subsequent muscle growth processes of juveniles fed a commercial diet for 3 months. When compared at similar body weights, initially HF diet-fed juveniles indeed had a lower mean diameter of white muscle fibres, a smaller number of large white muscle fibres, and lower expression levels of MyoD1 and myogenin. These findings demonstrated the strong effect of early feed composition on the muscle growth mechanisms of trout alevins and juveniles.

Satellite cell activation and populations on single muscle-fiber cultures from adult zebrafish (Danio rerio)

Satellite cells (SCs), stem cells in skeletal muscle, are mitotically quiescent in adult mammals until activated for growth or regeneration. In mouse muscle, SCs are activated by nitric oxide (NO), hepatocyte growth factor (HGF) and the mechanically induced NO-HGF signaling cascade. Here, the SC population on fibers from the adult, ectothermic zebrafish and SC responsiveness to activating stimuli were assessed using the model system of isolated fibers cultured at 27 and 21°C. SCs were identified by immunostaining for the HGF receptor, c-met, and activation was determined using bromodeoxyuridine uptake in culture or in vivo. In dose-response studies, SC activation was increased by treatment with the NO-donor drug isosorbide dinitrate (1 mmol l(-1)) or HGF (10 ng ml(-1)) to maximum activation at lower concentrations of both than in previous studies of mouse fibers. HGF-induced activation was blocked by anti-c-met antibody, and reduced by culture at 21°C. The effect of cyclical stretch (3 h at 4 cycles per minute) increased activation and was blocked by nitric oxide synthase inhibition and reduced by culture at 21°C. The number of c-met+ SCs per fiber increased rapidly (by 3 h) after stretching. The character of signaling in SC activation on zebrafish fibers, in particular temperature-dependent responses to HGF and stretch, gives new insights into the influence of ectothermy on regulation of muscle growth in teleosts and suggests the use of the single-fiber model system to explore the basis of fiber hyperplasia and the conservation of regulatory pathways between species.

Ploidy effects on genes regulating growth mechanisms during fasting and refeeding in juvenile rainbow trout (Oncorhynchus mykiss)

Diploid and triploid rainbow trout weighing approximately 3g were either fed for five weeks, or feed deprived for one week, followed by refeeding. During feed deprivation gastrointestinal somatic index decreased in diploids, but not triploids, and during refeeding, carcass growth rate recovered more quickly in triploids. Although not affected by ploidy, liver ghr2 and igfbp2b expression increased and igfbp1b decreased in fasted fish. Effects of ploidy on gene expression indicate potential mechanisms associated with improved recovery growth in triploids, which include decreased hepatic igfbp expression, which could influence IGF-I bioavailability, differences in tissue sensitivity to TGFbeta ligands due to altered tgfbr and smad expression, and differences in expression of muscle regulatory genes (myf5, mstn1a, and mstn1b). These data suggest that polyploidy influences the expression of genes critical to muscle development and general growth regulation, which may explain why triploid fish recover from nutritional insult better than diploid fish.

Molecular characterization and expression patterns of myogenin in compensatory growth of Megalobrama amblycephala

Myogenin (myog) is a muscle-specific basic helix-loop-helix (bHLH) transcription factor that plays an essential role in regulating skeletal muscle development and growth. To investigate molecular characterization of myog and the effect of starvation/refeeding on the gene expression, we isolated the myog cDNA sequence and analyzed the expression patterns using quantitative real-time polymerase chain reaction in Megalobrama amblycephala. Sequence analysis indicated that M. amblycephala myog shared an analogous structure with the highly conserved His/Cys-rich, bHLH and C-terminal helix III domains with other vertebrates. Sequence alignment and phylogenetic tree showed that M. amblycephala myog had the highest identity with the homologues of Ctenopharyngodon idella and Cyprinus carpio. Spatio-temporal expression patterns revealed that myog mRNA levels at the segmentation period and 12 h post-hatching (hph) were significantly higher than at other development stages (P<0.05). Furthermore, the highest myog expression level was predominantly observed in white muscle compared with the other types of muscle. Fish body weight continuously decreased during 21-day starvation and then significantly increased after 7days of refeeding and reached the similar level to the control at 21days of refeeding, indicating that the pattern of complete compensatory growth possibly occurred in M. amblycephala; meanwhile, the relative somatic growth rate after refeeding was also dramatically higher than the control group. In addition, the myog expression decreased during 21days of starvation and then exhibited a strong rebound effect after 7days of refeeding and subsequently declined gradually to the control level by 21days of refeeding.

Differential Expression of Myogenic Regulatory Factor Genes in the Skeletal Muscles of Tambaqui Colossoma macropomum (Cuvier 1818) from Amazonian Black and Clear Water

Hypothesizing that the Amazonian water system differences would affect the expression of muscle growth-related genes in juvenile tambaqui Colossoma macropomum (Cuvier 1818), this study aimed to analyze the morphometric data and expression of myogenic regulatory factors (MRFs) in the white and red muscle from tambaqui obtained from clear and black Amazonian water systems. All of the MRF transcript levels (myod, myf5, myogenin, and mrf4) were significantly lower in the red muscle from black water fish in comparison to clear water fish. However, in white muscle, only the myod transcript level was significantly decreased in the black water tambaqui. The changes in MRFs gene expression in muscle fibers of tambaqui from black water system provide relevant information about the environmental influence as that of water systems on gene expression of muscle growth related genes in the C. macropomum. Our results showed that the physical and chemical water characteristics change the expression of genes that promote muscle growth, and these results may be also widely applicable to future projects that aim to enhance muscle growth in fish that are of substantial interest to the aquaculture.