Analysis of myostatin gene structure, expression and function in zebrafish

Characterization of the myostatin gene in the neotropical species Piaractus mesopotamicus and the possibility of its use in genetic improvement programs

BACKGROUND

The myostatin gene has played an important role in the genetic improvement of the main species of economic importance; however, it has not yet been described for some Neotropical fish essential for aquaculture. This study aimed to characterize the myostatin gene of pacu, Piaractus mesopotamicus, and investigate the association of a microsatellite marker in this gene with the weight of fish.

METHODS AND RESULTS

The myostatin gene sequence was obtained after following a RACE-PCR strategy based on a partial mRNA sequence available in the GenBank database and the alignment of myostatin sequences from other fish species. The obtained sequence for the P. mesopotamicus gene was analyzed for short tandem repeats, and one dinucleotide was observed at the 3´untranslated region. A short tandem repeat polymorphism was verified in a wild population. Subsequently, the STR was evaluated in a test population of 232 animals in two 220 m² concrete tanks at the Aquaculture Center of Unesp. Eight alleles and 22 genotype combinations were identified. A significant association was observed between microsatellite marker polymorphisms and the weight traits (WEIGHT1 and WEIGHT2). Alleles 210, 222, 226, and 230 were found to favor weight gain.

CONCLUSIONS

In summary, this study contributes to the characterization of the myostatin gene in pacu fish and identifies an association between a STR and weight traits. Thus, this gene could be used as a target for genetic breeding using molecular strategies such as CRISPR and quantitative strategies such as marker-assisted selection, which would contribute to improving the production of the species.

Myostatin's marvels: From muscle regulator to diverse implications in health and disease

Myostatin, a member of the transforming growth factor-β superfamily, is a pivotal regulator of skeletal muscle growth in mammals. Its discovery has sparked significant interest due to its multifaceted roles in various physiological processes and its potential therapeutic implications. This review explores the diverse functions of myostatin in skeletal muscle development, maintenance and pathology. We delve into its regulatory mechanisms, including its interaction with other signalling pathways and its modulation by various factors such as microRNAs and mechanical loading. Furthermore, we discuss the therapeutic strategies aimed at targeting myostatin for the treatment of muscle-related disorders, including cachexia, muscular dystrophy and heart failure. Additionally, we examine the impact of myostatin deficiency on craniofacial morphology and bone development, shedding light on its broader implications beyond muscle biology. Through a comprehensive analysis of the literature, this review underscores the importance of further research into myostatin's intricate roles and therapeutic potential in human health and disease.

The key role of myostatin b in somatic growth in fishes derived from distant hybridization

The basic mechanism of heterosis has not been systematically and completely characterized. In previous studies, we obtained three economically important fishes that exhibit rapid growth, WR (WCC ♀ × RCC ♂), WR-II (WR ♀ × WCC ♂), and WR-III (WR-II ♀ × 4nAU ♂), through distant hybridization. However, the mechanism underlying this rapid growth remains unclear. In this study, we found that WR, WR-II, and WR-III showed muscle hypertrophy and higher muscle protein and fat contents compared with their parent species (RCC and WCC). Candidate genes responsible for this rapid growth were then obtained through an analysis of 12 muscle transcriptomes. Notably, the mRNA level of mstnb (myostatin b), which is a negative regulator of myogenesis, was significantly reduced in WR, WR-II, and WR-III compared with the parent species. To verify the function of mstnb, a mstnb-deficient mutant RCC line was generated using the CRISPR-Cas9 technique. The average body weight of mstnb-deficient RCC at 12 months of age was significantly increased by 29.57% compared with that in wild-type siblings. Moreover, the area and number of muscle fibers were significantly increased in mstnb-deficient RCC, indicating hypertrophy and hyperplasia. Furthermore, the muscle protein and fat contents were significantly increased in mstnb-deficient RCC. The molecular regulatory mechanism of mstnb was then revealed by transcription profiling, which showed that genes related to myogenesis (myod, myog, and myf5), protein synthesis (PI3K-AKT-mTOR), and lipogenesis (pparγ and fabp3) were highly activated in hybrid fishes and mstnb-deficient RCC. This study revealed that low expression or deficiency of mstnb regulates somatic growth by promoting myogenesis, protein synthesis, and lipogenesis in hybrid fishes and mstnb-deficient RCC, which provides evidence for the molecular mechanism of heterosis via distant hybridization.

Zebrafish as a Human Muscle Model for Studying Age-Dependent Sarcopenia and Frailty

Currently, there is an increase in the aging of the population, which represents a risk factor for many diseases, including sarcopenia. Sarcopenia involves progressive loss of mass, strength, and function of the skeletal muscle. Some mechanisms include alterations in muscle structure, reduced regenerative capacity, oxidative stress, mitochondrial dysfunction, and inflammation. The zebrafish has emerged as a new model for studying skeletal muscle aging because of its numerous advantages, including histological and molecular similarity to human skeletal muscle. In this study, we used fish of 2, 10, 30, and 60 months of age. The older fish showed a higher frailty index with a value of 0.250 ± 0.000 because of reduced locomotor activity and alterations in biometric measurements. We observed changes in muscle structure with a decreased number of myocytes (0.031 myocytes/μm2 ± 0.004 at 60 months) and an increase in collagen with aging up to 15% ± 1.639 in the 60-month group, corresponding to alterations in the synthesis, degradation, and differentiation pathways. These changes were accompanied by mitochondrial alterations, such as a nearly 50% reduction in the number of intermyofibrillar mitochondria, 100% mitochondrial damage, and reduced mitochondrial dynamics. Overall, we demonstrated a similarity in the aging processes of muscle aging between zebrafish and mammals.

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.

Transcriptional Knock-down of mstn Encoding Myostatin Improves Muscle Quality of Nile Tilapia (Oreochromis niloticus)

Myostatin (encoded by mstn) negatively regulates skeletal muscle mass and affects lipid metabolism. To explore the regulatory effects of mstn on muscle development and lipid metabolism in Nile tilapia (Oreochromis niloticus), we used antisense RNA to transcriptionally knock-down mstn. At 180 days, the body weight and body length were significantly higher in the mstn-knock-down group than in the control group (p < 0.05). Additionally, fish with mstn-knock-down exhibited myofiber hyperplasia but not hypertrophy. Oil red O staining revealed a remarkable increase in the area of lipid droplets in muscle in the mstn-knockdown group (p < 0.05). Nutrient composition analyses of muscle tissue showed that the crude fat content was significantly increased in the mstn-knock-down group (p < 0.05). The contents of saturated fatty acids, monounsaturated fatty acids, and polyunsaturated fatty acids were all significantly increased in the mstn-knock-down group (p < 0.05). Comparative transcriptome analyses revealed 2420 significant differentially expressed genes between the mstn-knock-down group and the control group. KEGG analysis indicates that disruptions to fatty acid degradation, glycerolipid metabolism, and the PPAR signaling pathway affect muscle development and lipid metabolism in mstn-knock-down Nile tilapia: acaa2, eci1, and lepr were remarkably up-regulated, and acadvl, lpl, foxo3, myod1, myog, and myf5 were significantly down-regulated (p < 0.05). These results show that knock-down of mstn results in abnormal lipid metabolism, acceleration of skeletal muscle development, and increased adipogenesis and weight gain in Nile tilapia.

Effects of Myostatin b Knockout on Offspring Body Length and Skeleton in Yellow Catfish (Pelteobagrus fulvidraco)

Based on obtaining mstnb gene knockout in Pelteobagrus fulvidraco, a study on the effect of the mstn gene on skeletal morphology and growth was performed by comparing the number and length of the vertebrae of mutant and wild-type fish in a sibling group of P. fulvidraco, combined with the differences in cells at the level of vertebral skeletal tissue. It was found that mstnb gene knockdown resulted in a reduction in the number of vertebrae, the length, and the intervertebral distance in P. fulvidraco, and these changes may be the underlying cause of the shorter body length in mutant P. fulvidraco. Further, histological comparison of the same sites in the mstn mutant and wild groups of P. fulvidraco also revealed that the number and density of osteocytes were greater in mstnb knockout P. fulvidraco than in wild-type P. fulvidraco. Our results demonstrated that when using genome editing technology to breed new lines, the effects of knockout need to be analyzed comprehensively and may have some unexpected effects due to insufficient study of the function of certain genes.

Myostatin-mediated regulation of skeletal muscle damage post-acute Aeromonas hydrophila infection in Nile tilapia (Oreochromis niloticus L.)

This study focuses on the relationship between myostatin (MyoS), myogenin (MyoG), and the growth hormone/insulin-like growth factor-1 (GH/IGF-1) axis for muscle growth and histopathological changes in muscle after an Aeromonas hydrophila infection. A total number of 90 Nile tilapia (55.85 g) were randomly allocated into two equal groups of three replicates each. The first group was an uninfected control group that was injected intraperitoneally (ip) with 0.2 ml phosphate buffer saline (PBS), while the second group was injected ip with 0.2 ml (1.3 × 10⁸ CFU/ml) Aeromonas hydrophila culture suspension. Sections of white muscle and liver tissues were taken from each group 24 h, 48 h, 72 h, and 1 week after infection for molecular analysis and histopathological examination. The results revealed that with time progression, the severity of muscle lesions increased from edema between bundles and mononuclear inflammatory cell infiltration 24 h post-challenge to severe atrophy of muscle bundles with irregular and curved fibers with hyalinosis of the fibers 1 week postinfection. The molecular analysis showed that bacterial infection was able to induce the muscle expression levels of GH with reduced ILGF-1, MyoS, and MyoG at 24 h postinfection. However, time progression postinfection reversed these findings through elevated muscle expression levels of MyoS with regressed expression levels of muscle GH, ILGF-1, and MyoG. There have been no previous reports on the molecular expression analysis of the aforementioned genes and muscle histopathological changes in Nile tilapia following acute Aeromonas hydrophila infection. Our findings, collectively, revealed that the up-and down-regulation of the myostatin signaling is likely to be involved in the postinfection-induced muscle wasting through the negative regulation of genes involved in muscle growth, such as GH, ILGF-1, and myogenin, in response to acute Aeromonas hydrophila infection in Nile tilapia, Oreochromis niloticus.

Development of breast muscle parameters, glycogen reserves, and myogenic gene expression in goslings during pre- and post-hatching periods

This study aimed to better understand the development patterns of breast muscle and glycogen reserves in goslings during pre- and post-hatching periods. The timepoints for sampling were embryonic days 23 and 27 of hatching and days 1, 4, and 7 post hatching. We found that the body weight of goslings increased with age. The small intestine developed with age and remained reasonably constant on day 4 post hatching. The breast muscle development decreased with age and stayed relatively stable on day 1 post hatching. The diameter of myofiber increased prior to hatching and then decreased while hatching. The development patterns of breast muscle glycogen reserves were similar to the diameter of myofiber. In contrast, the contents of liver glycogen began to decrease before hatching and then increased rapidly after hatching. Moreover, the expression of Myf-5 increased with age. The expression of MSTN was maintained at high levels prior to hatching, dropped immediately after hatching, and then gradually increased with age. Additionally, we also observed that the glycogen content in the breast muscle was positively correlated with the diameter of the myofiber. The liver glycogen content was positively correlated to the relative weight of the breast muscle, the diameter of the myofiber, and the breast muscle glycogen content. The development pattern of the myofiber was synchronized with the change in the MSTN/Myf-5 ratio. This study provided a profile to understand the development patterns of breast muscle, glycogen reserves, and myogenic gene expression in goslings, which was beneficial to understanding the characteristics of energy reserves during the early life of goslings.

Disruption of mstn Gene by CRISPR/Cas9 in Large Yellow Croaker (Larimichthys crocea)

The large yellow croaker (Larimichthys crocea) plays an economically vital role in the marine aquaculture in China. Suffering from infection of bacteria and protozoon, effect of extreme weather and stress from high-density farming, genome editing is thought to be an important tool applied to L. croea for enhancing commercial traits such as growth rate, disease resistance, and nutrition component. In this study, we identified two mstn genes in L. croea and investigated the different phylogenetic clades, gene structures, and conserved syntenic relationships. To obtain fast-growing large yellow croaker, we specially selected two validated targets for mstnb knockout, which was homologous to mammalian myostatin gene (MSTN) and downregulated skeletal muscle growth and development. Five significant mutation types were generated in two mosaic mutants by transferring specific CRISPR/Cas9 RNPs (ribonucleoprotein) into the one-cell fertilized embryos based on CRISPR/Cas9 technology. Subsequently, we also elucidated the obstacles and possible measures to improve the success rate of inducing modified large yellow croaker. Our results would provide valuable method and reference for facilitating genome editing programs of the large yellow croaker in the future.

Effect of quercetin on muscle growth and antioxidant status of the dark sleeper Odontobutis potamophila

Quercetin is a flavanol beneficial in reducing fat, promoting muscle growth, and Anti-oxidation. To study its effects in freshwater fish, the full-length cDNA of the follistatin (FST) and myostatin (MSTN) genes of the dark sleeper Odontobutis potamophila were cloned for the first time. Juvenile individual O. potamophila was exposed to quercetin at one of four concentrations (0, 2.5, 5, and 10 mg/L) for 21 days. The expression level of MSTN which inhibits muscle growth in the quercetin solution was lower than in the unexposed control group. The genes that promote muscle growth are in TGF-β superfamily like FST, TGF-β1 (transforming growth factor-beta 1), and Myogenic regulatory factors (MRFs) like Myf5 (myogenic factor 5), MyoD (myogenic differentiation), MyoG (myogenin), were higher than in the control group. Apolipoprotein and growth hormone receptor transcription levels in the quercetin-treated fish were significantly lower than in the control group. The concentrations of triglyceride, low-density lipoprotein cholesterol, and high-density lipoprotein cholesterol in the muscle tissue decreased, and the lipid-lowering function of quercetin was also demonstrated at the biochemical level. In this study, we analyzed the mRNA levels of AKT, Keap1 (kelch-like ECH-associated protein 1), Nrf2 (NF-E2-related factor 2) oxidation-related genes in the Nrf2/ARE antioxidant pathway, and Malondialdehyde (MDA), catalase (CAT) activity and glutathione (GSH) content in the hepatopancreas of O. potamophila after quercetin treatment, the mRNA expression of AKT, Nrf2 and CAT activity and GSH content are higher than in the control group. Quercetin enhances antioxidant properties and positively affects muscle growth. The results showed that quercetin has no significant effects on the growth performance of O. potamophila, but is effective in increasing muscle growth rate and lowering muscle fat content.

Myostatin: a multifunctional role in human female reproduction and fertility - a short review

Myostatin (MSTN) is member of the transforming growth factor β (TGF-β) superfamily and was originally identified in the musculoskeletal system as a negative regulator of skeletal muscle growth. The functional roles of MSTN outside of the musculoskeletal system have aroused researchers' interest in recent years, with an increasing number of studies being conducted in this area. Notably, the expression of MSTN and its potential activities in various reproductive organs, including the ovary, placenta, and uterus, have recently been examined. Numerous studies published in the last few years demonstrate that MSTN plays a critical role in human reproduction and fertility, including the regulation of follicular development, ovarian steroidogenesis, granule-cell proliferation, and oocyte maturation regulation. Furthermore, findings from clinical samples suggest that MSTN may play a key role in the pathogenesis of several reproductive disorders such as uterine myoma, preeclampsia (PE), ovary hyperstimulation syndrome (OHSS), and polycystic ovarian syndrome (PCOS). There is no comprehensive review regarding to MSTN related to the female reproductive system in the literature. This review serves as a summary of the genes in reproductive medicine and their potential influence. We summarized MSTN expression in different compartments of the female reproductive system. Subsequently, we discuss the role of MSTN in both physiological and several pathological conditions related to the female fertility and reproduction-related diseases.

Growth, Hemato-Biochemical Parameters, Body Composition, and Myostatin Gene Expression of Clarias gariepinus Fed by Replacing Fishmeal with Plant Protein

Simple Summary

The costs of feed ingredients in the aquaculture sector are one of the main problems impacting the success or failure of a business. The key ingredient in aquafeeds and the costliest among them is fish meal (FM). Therefore, great consideration was given to the use of different types of plant protein (PP) meals in aquafeeds (soybean and sunflower meal). In this study, fish were divided into five groups, with each group in triplicate (30 fish/group; 10 fish/replicate). Group 1 was fed the control diet consisting of 15% FM and 41% soybean meal. The other four groups (D1, D2, D3, and D4) were fed experimental diets, where FM was replaced gradually by plant protein sources (33, 50, 66, and 100% soybean meal and sunflower meal) for 60 days. In conclusion, partial or total replacement of FM with a plant protein source (soybean and sunflower meal) showed similar growth performance and body composition with greater economic efficiency.

Abstract

In this study, we evaluated the consequences of replacement of fishmeal with plant protein sources (soybean and sunflower meal) on fish growth parameters, haemato-biochemical factors, body composition, and myostatin gene expression of Clarias gariepinus. A total of 150 C. gariepinus were organized in glass aquaria into five investigational groups, with each group in triplicate (30 fish/group; 10 fish/replicate). Group 1 was fed a control diet (15% fishmeal). The other groups were fed diets where fishmeal was replaced gradually with plant protein, with 10% fishmeal in the second group (D1), 7.5% fishmeal in the third group (D2), 5% fishmeal in the fourth group (D3), and 0% fishmeal in the fifth group (D4). There were no significant differences regarding growth performances and body composition among the groups, except that the feed conversion ratio was improved in D4. The different diet types did not affect hematologic parameters and blood indices. Serum growth hormone and amylase levels also revealed no significant (p = 0.09 and 0.55, respectively) differences among the groups, while serum lipase levels decreased significantly (p = 0.000) due to partial (D2) or complete (D4) substitution of fishmeal with plant protein. The replacement of fishmeal had no effects on liver (p = 0.51) and kidney functions (p = 0.34). However, D4 showed the best profit and economic efficiency compared to the other groups. Altogether, we concluded that substitution of fishmeal with plant protein sources is economically beneficial and may be without any adverse effects on growth parameters, body composition, or hematologic and biochemical parameters, but with the addition of synthetic amino acids.

Morphometric and population genomic evidence for species divergence in the Chimarrichthys fish complex of the Tibetan Plateau

The uplift of the Tibetan Plateau altered the environmental conditions of the local area substantially. Here, we conducted a comprehensive investigation based on morphometrics, population genomics, and climatic factors to evaluate phenotypic and genome-level variations in a radiation of Chimarrichthys catfish endemic to the Plateau. Discriminant function analysis showed phenotypic differences of Chimarrichthys between rivers with respect to elevation. Genetic structure analysis based on 6606 single nucleotide polymorphisms (SNPs) deduced genetic differences between rivers, and species delimitation indicated that the Chimarrichthys fish complex could be divided into three species. Restriction site-associated DNA tags were mapped to the gene sets of Glyptosternon maculatum, and matches were searched against databases for Gene Ontology annotation. Genomic regions exhibiting marked differences among localities represented a range of biological functions, including growth (gdf11), bone development (bmp8a), cellular response to light stimulus (opn3), regulation of the rhodopsin-mediated signalling pathway (grk1), immune response (rag1 and ung), reproductive process (antxr2), and regulation of intracellular iron levels (ireb2). The tag44126, where gene gdf11 is located, was identified as an outlier exhibiting divergence between rivers with altitude differences, and the SNP is thymine (T) in Dadu and Yalong River (~2700 m), but guanine (G) in Jinsha and Qingyi rivers (~2200 and ~ 684 m), suggesting a possible effect of altitude on its differentiation.

Activin A affects feeding by promoting the inner diameter and muscle development of the pharynx and oesophagus in zebrafish (Danio rerio) larvae

Activin A belongs to the superfamily of transforming growth factor-β and plays an important role in hormone regulation and tissue development. However, few research studies have been conducted on the effect of activin A on feeding organs in fish. In this study, the zebrafish (Danio rerio) larvae were treated with 1 ng ml^-1 activin A for 8 days continuously. The haematoxylin and eosin (H&E) staining section results revealed that the transverse inner diameter of the pharynx and oesophagus significantly increased on the third and eighth days after treatment compared with the control group (P < 0.05). On the eighth day, the cross-sectional area of the pharyngeal muscle increased by 8638 μm² compared to the control group (P < 0.05). The RNA in situ hybridization results also showed that the expression of skeletal muscle-specific genes (myog and myod) was significantly increased in pharyngeal muscle on the eighth day. Furthermore, the qRT-PCR results showed the expression of gh gene was significantly increased on the eighth day (P < 0.05). At the same time, more larvae in activin A group were able to feed larger brine shrimp (Artemia) than in the control group on the eighth day. In conclusion, activin A could affect feeding by promoting the inner diameter and muscle development of the pharynx and oesophagus in zebrafish larvae. This study is the first to report that the development of the pharynx and oesophagus can directly affect food intake in fish larvae, which provides a theoretical basis for the study of food intake of fish at an early stage.

Characterization of Myostain (MSTN) and Myogenic Differentiation Antigen (MyoD) and the Effect of Dexamethasone on Their Expression in Large-Scale Loach Paramisgurnus dabryanus

Myostatin (MSTN) and myogenic differentiation antigen (MyoD) play an essential role in specification and differentiation of skeletal muscle. However, the role of stress in the regulation of MyoD and MSTN has not been fully revealed and more evidence should be provided. Here, we reported the cloning and expressional analyses of MSTN and MyoD in Large-scale Loach Paramisgurnus dabryanus (hereafter PdMSTN and PdMyoD). Injecting individuals with 0, 60, 600, and 1,200 μg/kg dexamethasone (DXM) for five consecutive days resulted in a dose-dependent change of PdMSTN and PdMyoD expression. The expression of PdMSTN was upregulated with increasing DXM concentrations, while PdMyoD expression was downregulated. The changes in the expression of these genes at different time points for 10 consecutive days were studied after individuals were treated with 600 μg/kg DXM. Compared with the control group, PdMSTN expression decreased and PdMyoD expression increased before 12 h, and both PdMSTN and PdMyoD expression levels increased at 24 h, which was significantly higher than those in control group. At a prolonged treatment of 5-10 d, expression levels of PdMSTN and PdMyoD had significantly reduced. The results indicate that both PdMyoD and PdMSTN are involved in DXM-induced stress in Large-scale Loach.

Dietary Antioxidant Supplementation Promotes Growth in Senegalese Sole Postlarvae

Somatic growth is a balance between protein synthesis and degradation, and it is largely influenced by nutritional clues. Antioxidants levels play a key role in protein turnover by reducing the oxidative damage in the skeletal muscle, and hence promoting growth performance in the long-term. In the present study, Senegalese sole postlarvae (45 days after hatching, DAH) were fed with three experimental diets, a control (CTRL) and two supplemented with natural antioxidants: curcumin (CC) and grape seed (GS). Trial spanned for 25 days and growth performance, muscle cellularity and the expression of muscle growth related genes were assessed at the end of the experiment (70 DAH). The diets CC and GS significantly improved growth performance of fish compared to the CTRL diet. This enhanced growth was associated with larger muscle cross sectional area, with fish fed CC being significantly different from those fed the CTRL. Sole fed the CC diet had the highest number of muscle fibers, indicating that this diet promoted muscle hyperplastic growth. Although the mean fiber diameter did not differ significantly amongst treatments, the proportion of large-sized fibers (>25 μm) was also higher in fish fed the CC diet suggesting increased hypertrophic growth. Such differences in the phenotype were associated with a significant up-regulation of the myogenic differentiation 2 (myod2) and the myomaker (mymk) transcripts involved in myocyte differentiation and fusion, respectively, during larval development. The inclusion of grape seed extract (GS diet) resulted in a significant increase in the expression of myostatin1. These results demonstrate that both diets (CC and GS) can positively modulate muscle development and promote growth in sole postlarvae. This effect is more prominent in CC fed fish, where increased hyperplastic and hypertrophic growth of the muscle was associated with an upregulation of myod2 and mymk genes.

Myostatin-1 Inhibits Cell Proliferation by Inhibiting the mTOR Signal Pathway and MRFs, and Activating the Ubiquitin-Proteasomal System in Skeletal Muscle Cells of Japanese Flounder Paralichthys olivaceus

Myostatin (MSTN) is a negative regulator of skeletal muscle growth and development. The mechanisms of fish MSTN involved in muscle growth are not fully understood. In the present study, knockdown and overexpression of mstn-1 was performed in cultured Japanese flounder muscle cells to investigate the molecular function and the underlying mechanism of fish MSTN-1. Results showed that mstn-1 knockdown significantly induced cell proliferation and the mRNA expression of myogenic regulatory factors (MRFs), while overexpression of mstn-1 led to a significant decrease of cell proliferation and a suppression of the MRFs mRNA expression. The overexpression of mstn-1 also significantly increased the mRNA expression of ubiquitin–proteasomal pathway of proteolysis genes including muscle RING-finger protein 1 (murf-1) by 204.1% (p = 0.024) and muscle atrophy F-box protein (mafbx) by 165.7% (p = 0.011). However, mystn-1 overexpression inhibited the activation of mTOR signal pathway and the AKT/FoxO1 pathway through decreasing phosphorylation of AKT at Ser 473 by 56.0% (p = 0.001). Meanwhile, mystn-1 overexpression increased the dephosphorylation and nuclear localization of FoxO1 by 394.9% (p = 0.005). These results demonstrate that mstn-1 in Japanese flounder has the effects of inhibiting cell proliferation and growth, and the mTOR and AKT/FoxO1 pathways participated in these biological effects.

Characterization of two myostatin genes in pufferfish Takifugu bimaculatus: sequence, genomic structure, and expression

Myostatin (MSTN) is a negative regulator of muscle growth, which restrains the proliferation and differentiation of myoblasts. To understand the role of two mstn genes of Takifugu bimaculatus, the full-length cDNAs of 1131 bp Tbmstn1 and 1,080 bp Tbmstn2 were obtained from the T. bimaculatus' genomic database, which encodes 376 and 359 amino acids, respectively. The results of qRT-PCR showed that Tbmstn1 was expressed in the eye, kidney, spleen, skeletal muscle, gill, and brain, and the expression level in the skeletal muscle was extremely significantly higher than in other examined tissues. Tbmstn2 was expressed in the skin, skeletal muscle, gill, and brain, and had the highest expression in the skeletal muscle, followed by expression in the brain. Meanwhile, in different stages of embryonic development, the expression of Tbmstn1 started from the gastrula stage. Its expression in the eye-pigment formation stage and hatching stage was significantly higher than that in other stages. The Tbmstn2 was expressed in all examined embryonic stages with different levels, and the highest expression was detected in the eye-pigment formation stage. These results suggested that Tbmstn1 and Tbmstn2 may involve in the development of skeletal muscle, and Tbmstn2 may be related to the formation of nervous system.

Expression profiles of growth-related genes in two Nile tilapia strains and their crossbred provide insights into introgressive breeding effects

The Nile tilapia (Oreochromis niloticus) is a prominent farmed fish in aquaculture worldwide. Crossbreeding has recently been carried out between the Red-Stirling and the wt Chitralada strains of Nile tilapia, producing a heterotic hybrid (7/8 Chitralada and 1/8 Red-Stirling) that combines the superior growth performance of the Chitralada with the reddish coloration of the Red-Stirling strain. While classical selective breeding and crossbreeding strategies are well known, the molecular mechanisms underlying the phenotypic expression of economically advantageous traits in tilapia remain largely unknown. Molecular investigations have shown that variable expression of growth hormone (gh), insulin-like growth factors (igf1 and 2) and somatolactin (smtla) - components of the growth hormone/insulin-like growth factor (GH/IGF) axis - and myostatin (mstn) genes can affect traits of economic relevance in farmed animals. The aim of this study was to assess and compare the gene expression signature among Chitralada, Red-Stirling and their backcross hybrid in order to gain insights into the effects of introgressive breeding in modulation of the GH/IGF axis. Gene expression analyses in distinct tissues showed that most genes of the GH/IGF axis were up-regulated and mstn was down-regulated in backcross animals in comparison with Red-Stirling and Chitralada animals. These gene expression profiles revealed that backcross animals displayed a distinctive expression signature, which attests to the effectiveness of the introgressive breeding technique. Our findings also suggest that the GH/IGF axis and mstn genes might be candidate markers for fish performance and prove useful within genetic improvement programs aimed at the production of superior-quality tilapia strains using introgressive breeding.

Identification and Characterization of a Non-muscular Myostatin in the Nile Tilapia

The growth and differentiation factor Myostatin (MSTN, also known as GDF8) negatively regulates skeletal muscle development and growth in vertebrates. Most fish genomes contain two or more mstn genes, which are expressed in muscle and other tissues. Yet, in the genome of Nile tilapia (Oreochromis niloticus), which is one of the world's most important aquaculture fish species, only one mstn gene has previously been identified. Here, we identify a second mstn gene in Nile tilapia. We show that it clusters phylogenetically with other piscine mstn2 genes and that it shares chromosomal synteny with the human and zebrafish orthologs. We further show that mstn2 is not expressed in red or white muscles of Nile tilapia, but rather that its main site of expression is the brain. To determine which physiological functions are correlated with mstn expression, adult Nile tilapia were exposed to various environmental conditions and their effect on mstn1 and mstn2 expression in the brain and muscles was measured using real-time PCR. We found that the centrally- and muscle-expressed mstn genes differ in their responsiveness to diverse challenges, suggesting differential gene- and tissue-specific regulation of their expression. Metabolic and stress marker analyses showed that the altered mstn expression is not regulated by classical stress response. Taken together, our findings expand the understanding of the MSTN system in Nile tilapia and provide evolutionary insight into its function.

Molecular characterization, expression analysis of myostatin gene and its negative regulation by miR-29b-3p in Chinese concave-eared frogs (Odorrana tormota)

The molecular characteristics, expression patterns and functions of the amphibian myostatin (MSTN) gene are unknown. Here, we isolated a full-length Odorrana tormota MSTN cDNA sequence of 1701 bp (Ot-MSTN), containing a putative N-terminal signal peptide, a TGF-β propeptide domain and an active peptide. Ot-MSTN was expressed in 9 selected tissues examined, and the highest level of expression was in thigh muscle, followed by brain and female gonadal tissue. The expression of Ot-MSTN in multiple O. tormota tissues supported that the activities of MSTN may be not limited to skeletal muscle. Ot-MSTN expression was decreased from stage 31 to stage 40, while the growth rate was increased. The expression of Ot-MSTN in adult male frogs increased with age, indicating that adult male frogs may inhibit the continued hypertrophy of thigh muscle fibers and decrease the growth rate of thigh muscle to ensure muscles do not grow too large. Luciferase reporter assays showed that miR-29b-3p directly targeted the 3'-UTR of Ot-MSTN. miR-29b-3p expression in the thigh muscle of 2 yrs. females who grew faster was significantly lower than that of the slow-growing 2 yrs. male individuals, which showed an opposite trend with Ot-MSTN expression. In addition，miR-29b-3p expression reversed trends of Ot-MSTN expression at different developmental stages in thigh muscle. Therefore, these data indicate that miR-29-3p may negatively regulate the expression of MSTN and regulate thigh muscle growth and development in O. tormota.

The Dietary Lipid Content Affects the Tissue Gene Expression of Muscle Growth Biomarkers and the GH/IGF System of Pejerrey (Odontesthes bonariensis) Juveniles

Gene expression of growth hormone receptors (GHRs), insulin-like growth factors (IGFs), myostatin (MSTN) and myogenin (MyoG) was analyzed in juveniles pejerrey fed with graded levels of lipids (L): 6% (L6), 10% (L10), 25% (L25). After 14 weeks, no changes were found in liver GHR-I GHR-II and IGF-II mRNA levels whereas IGF-I decreased in L10 and L25. Muscle GHR-I gene expression increased in L25 whereas GHR-II, IGF-II and MyoG were higher in L6. IGF-I and MSTN expression was not affected by the different diets. Adipose IGF-I mRNA levels decreased in L10. Correlations between body weight and members of GH/IGF system in liver and skeletal muscle were found only in L10 group. Correlations found in L10 group between both liver and skeletal muscle GHR-I and IGF-I were lost in either L6 or L25 groups. Thus, fish fed with apparently unbalanced dietary lipid contents (6% and 25%) exhibit a compensatory regulation of systemic and local components of the GH/IGF axis. Furthermore, the marked inhibition of muscle MyoG gene expression in L25 might limit excessive lipid deposition and fish growth. Our data suggest that a dietary lipid contents of 10% would promote a particular adjustment of the endocrine and autocrine/paracrine GH/IGF system, stimulating body growth and perhaps muscle hyperplasia. On the other hand, a higher dietary lipid content would uncouple the GH/IGF system, reducing hepatic IGF-I, while slightly increasing hepatic GHR-I, probably to prompt lipolysis.

Gene structure, recombinant expression and function characterization of Siniperca chuatsi Fsrp-3

A full-length complementary (c)DNA sequence encoding follistatin-related protein 3 (fsrp-3) was determined from skeletal muscle in Chinese mandarin fish Siniperca chuatsi, its molecular structure was characterised and its function suggested. The putative structure of S. chuatsi Fsrp-3 contains an N-terminal domain and two follistatin domains. Quantitative reverse-transcription (qRT)-PCR assays revealed that fsrp-3 messenger (m)RNA was differentially expressed among assayed tissues and was highly expressed in heart and intestine. fsrp-3 mRNA exhibited increasing expression from the larval to the juvenile stage (500 g). To investigate the potential function of S. chuatsi fsrp-3 in muscle growth, we constructed a Fsrp-3 prokaryotic expression system and injected the purified Fsrp-3 fusion protein into the dorsal muscle. Fsrp-3 administration significantly influenced cross-section area, satellite cell activation frequency and nuclear density of S. chuatsi muscle fibres. Following Fsrp-3 treatment, the expression of myogenic regulatory factors was up-regulated and decline in the expression of myostatin was observed. The study revealed that Fsrp-3 may affect muscle growth by regulating myogenic regulatory factor expression and antagonizing myostatin function to initiate satellite cell activation and differentiation in S. chuatsi.

Myostatin gene promoter: structure, conservation and importance as a target for muscle modulation

Myostatin (MSTN) is one of the key factors regulating myogenesis. Because of its role as a negative regulator of muscle mass deposition, much interest has been given to its protein and, in recent years, several studies have analysed MSTN gene regulation. This review discusses the MSTN gene promoter, focusing on its structure in several animal species, both vertebrate and invertebrate. We report the important binding sites considering their degree of phylogenetic conservation and roles they play in the promoter activity. Finally, we discuss recent studies focusing on MSTN gene regulation via promoter manipulation and the potential applications they have both in medicine and agriculture.

Recombinant porcine myostatin propeptide generated by the Pichia pastoris elevates myoblast growth and ameliorates high-fat diet-induced glucose intolerance

Myostatin (MSTN) was identified as a negative regulator of skeletal muscle growth. MSTN inhibition by myostatin propeptide (MSPP) increased skeletal muscle mass, myofiber growth and muscle force. Thus, this study was designed to produce wild-type porcine MSPP (WT-MSPP) and its mutated form (D75A-MSPP) in yeast Pichia pastoris and to investigate its potential enhancement of myoblast growth and differentiation. In an in vitro study, C2C12 myoblasts were treated with the purified WT-MSPP or D75A-MSPP (10 μg/mL) in either a regular culture medium or in a differentiation medium for 72 h. In an animal trial, post-weaning C57BL/6 mice fed with a high-fat diet (HFD) were administered WT-MSPP or D75A-MSPP for 6 weeks. The results showed that C2C12 myoblasts treated with the purified WT-MSPP or D75A-MSPP could dramatically promote cell proliferation. Both myoD and myogenin were significantly increased (p < .05) after WT-MSPP or D75A-MSPP treatment. D75A-MSPP was particularly more effective than WT-MSPP in promoting myotube formation (p < .05). The post-weaning mice treated with D75A-MSPP significantly increased both body and muscle weights compared with the mock and WT-MSPP groups (p < .05). Furthermore, the mice treatment with D75A-MSPP could prevent increased glucose injection from inducing glucose elevation. Our data indicated that a mutant-type MSPP (D75A-MSPP) was superior to WT-MSPP in effectively enhancing myofiber growth due to the highly resistant to proteolytic cleavage by the bone morphogenetic protein-1/tolloid (BMP-1/TLD) and thus has potential applications for clinical muscle wasting diseases or for increasing muscle mass in meat-producing animals.

Using CRISPR/Cas9-mediated gene editing to further explore growth and trade-off effects in myostatin-mutated F4 medaka (Oryzias latipes)

Myostatin (MSTN) suppresses skeletal muscle development and growth in mammals, but its role in fish is less well understood. Here we used CRISPR/Cas9 to mutate the MSTN gene in medaka (Oryzias latipes) and evaluate subsequent growth performance. We produced mutant F0 fish that carried different frameshifts in the OlMSTN coding sequence and confirmed the heritability of the mutant genotypes to the F1 generation. Two F1 fish with the same heterozygous frame-shifted genomic mutations (a 22 bp insertion in one allele; a 32 bp insertion in the other) were then crossbred to produce subsequent generations (F2~F5). Body length and weight of the MSTN-/- F4 medaka were significantly higher than in the wild type fish, and muscle fiber density in the inner and outer compartments of the epaxial muscles was decreased, suggesting that MSTN null mutation induces muscle hypertrophy. From 3~4 weeks post hatching (wph), the expression of three major myogenic related factors (MRFs), MyoD, Myf5 and Myogenin, was also significantly upregulated. Some medaka had a spinal deformity, and we also observed a trade-off between growth and immunity in MSTN-/- F4 medaka. Reproduction was unimpaired in the fast-growth phenotypes.

Characterization of a molt-related myostatin gene (FmMstn) from the banana shrimp Fenneropenaeus merguiensis

Myostatin is an important member of the transforming growth factor (TGF) family that functions to regulate muscle growth in animals. In this study, the myostatin gene (FmMstn) and two slightly different (short and long forms) cDNAs of the banana shrimp Fenneropenaeus merguiensis were cloned and characterized. Similar to Mstn gene of the scallop, fish and mammal, FmMstn gene consists of 3 exons and 2 introns. The 2kb upstream promoter region of the FmMstn gene consists of putative response elements for myocyte enhancing factor (MEF2) and E-box factors. The longest open reading frame of the short Mstn consists of 1260bp encoding for a protein with 420 amino acid residues. The long FmMstn is almost identical to the short FmMstn with the exception of 8 amino acid insertions. FmMstn is most similar to the Mstn of Litopenaeus vannamei and Penaeus monodon sharing >92-98% amino acid sequence identity. Multiple sequence alignment results revealed high degree of amino acid conservation of the cysteine residues and mature peptide of the FmMstn with Mstn from other animals. FmMstn transcript was detected in the heart, muscle, optic nerve and thoracic ganglion. FmMstn transcript level in muscle is higher in early postmolt, decreases in intermolt and increases again towards ecdysis. Higher expression level of FmMstn is also observed in smaller shrimp of the same age. Knock-down of FmMstn gene by RNAi can cause a significant increase in molt cycle duration and failure of some shrimp to undergo ecdysis. Direct DNA sequencing results revealed that FmMstn gene is highly polymorphic and several potential SNPs have been identified. Some SNPs are associated with the size difference of the shrimp. In summary, the result of this study indicates that shrimp FmMstn gene is molt/growth-related and the presence of SNP suggests that it could be a candidate gene for shrimp genetic improvement research.

Quercetin, a natural product supplement, impairs mitochondrial bioenergetics and locomotor behavior in larval zebrafish (Danio rerio)

Quercetin is a natural product that is sold as a supplement in health food stores. While there are reported benefits for this flavonoid as a dietary supplement due to antioxidant properties, the full scope of its biological interactions has not been fully addressed. To learn more about the mechanisms of action related to quercetin, we exposed zebrafish (Danio rerio) embryos to 1 and 10μg/L quercetin for 96h starting at 3h post fertilization. Quercetin up to 10μg/L did not induce significant mortality in developing fish, but did increase prevalence of an upward-curved dorsal plane in hatched larvae. To determine whether this developmental defect was potentially related to mitochondrial bioenergetics during development, we measured oxygen consumption rate in whole embryos following a 24-hour exposure to quercetin. Basal mitochondrial and ATP-linked respiration were decreased at 1 and 10μg/L quercetin, and maximal respiration was decreased at 10μg/L quercetin, suggesting that quercetin impairs mitochondrial bioenergetics. This is proposed to be related to the deformities observed during development. Due to the fact that ATP production was affected by quercetin, larval behaviors related to locomotion were investigated, as well as transcriptional responses of six myogenesis transcripts. Quercetin at 10μg/L significantly reduced the swimming velocity of zebrafish larvae. The expression levels of both myostatin A (mstna) and myogenic differentiation (myoD) were also altered by quercetin. Mstna, an inhibitory factor for myogenesis, was significantly increased at 1μg/L quercetin exposure, while myoD, a stimulatory factor for myogenesis, was significantly increased at 10μg/L quercetin exposure. There were no changes in transcripts related to apoptosis (bcl2, bax, casp3, casp7), but we did observe a decrease in mRNA levels for catalase (cat) in fish exposed to each dose, supporting an oxidative stress response. Our data support the hypothesis that quercetin may affect locomotion and induce deformities in zebrafish larvae by diminishing ATP production and by altering the expression of transcripts related to muscle formation and activity.

Dietary sodium propionate affects mucosal immune parameters, growth and appetite related genes expression: Insights from zebrafish model

Propionate is a short-chain fatty acid (SCFA) that improves physiological and pathophysiological properties. However, there is limited information available about the effects of SCFAs on mucosal immune parameters as well as growth and appetite related genes expression. The aim of the present study was to evaluate the effect of sodium propionate (SP) intake on the mucosal immune parameters, growth and appetite related genes expression using zebrafish (Danio rerio) as model organism. Zebrafish fed control or diet supplemented with different levels (0.5, 1 and 2%) of SP for 8weeks. At the end of feeding trial, the expression of the key genes related to growth and appetite (GH, IGF1, MYSTN and Ghrl) was evaluated. Also, mucosal immune parameters (Total Ig, lysozyme and protease activity) were studied in skin mucus of zebrafish. The results showed that dietary administration of SP significantly (P<0.05) up-regulated the expression of GH, IGF1 and down-regulated MYSTN gene. Also, feeding zebrafish with SP supplemented diet significantly increased appetite related gene expression (P<0.05) with a more pronounced effect in higher inclusion levels. Compared with control group, the expression of appetite related gene (Ghrl) was remarkably (P<0.05) higher in SP fed zebrafish. Also, elevated mucosal immune parameters was observed in zebrafish fed SP supplemented diet. The present results revealed beneficial effects of dietary SP on mucosal immune response and growth and appetite related genes expression. These results also highlighted the potential use of SP as additive in human diets.

Andre M, Svenson K, Morris C, Tchistiakova L. Beyond CDR-grafting: Structure-guided humanization of framework and CDR regions of an anti-myostatin antibody

Antibodies are an important class of biotherapeutics that offer specificity to their antigen, long half-life, effector function interaction and good manufacturability. The immunogenicity of non-human-derived antibodies, which can be a major limitation to development, has been partially overcome by humanization through complementarity-determining region (CDR) grafting onto human acceptor frameworks. The retention of foreign content in the CDR regions, however, is still a potential immunogenic liability. Here, we describe the humanization of an anti-myostatin antibody utilizing a 2-step process of traditional CDR-grafting onto a human acceptor framework, followed by a structure-guided approach to further reduce the murine content of CDR-grafted antibodies. To accomplish this, we solved the co-crystal structures of myostatin with the chimeric (Protein Databank (PDB) id 5F3B) and CDR-grafted anti-myostatin antibody (PDB id 5F3H), allowing us to computationally predict the structurally important CDR residues as well as those making significant contacts with the antigen. Structure-based rational design enabled further germlining of the CDR-grafted antibody, reducing the murine content of the antibody without affecting antigen binding. The overall "humanness" was increased for both the light and heavy chain variable regions.

Identification of Deleterious Mutations in Myostatin Gene of Rohu Carp (Labeo rohita) Using Modeling and Molecular Dynamic Simulation Approaches

The myostatin (MSTN) is a known negative growth regulator of skeletal muscle. The mutated myostatin showed a double-muscular phenotype having a positive significance for the farmed animals. Consequently, adequate information is not available in the teleosts, including farmed rohu carp, Labeo rohita. In the absence of experimental evidence, computational algorithms were utilized in predicting the impact of point mutation of rohu myostatin, especially its structural and functional relationships. The four mutations were generated at different positions (p.D76A, p.Q204P, p.C312Y, and p.D313A) of MSTN protein of rohu. The impacts of each mutant were analyzed using SIFT, I-Mutant 2.0, PANTHER, and PROVEAN, wherein two substitutions (p.D76A and p.Q204P) were predicted as deleterious. The comparative structural analysis of each mutant protein with the native was explored using 3D modeling as well as molecular-dynamic simulation techniques. The simulation showed altered dynamic behaviors concerning RMSD and RMSF, for either p.D76A or p.Q204P substitution, when compared with the native counterpart. Interestingly, incorporated two mutations imposed a significant negative impact on protein structure and stability. The present study provided the first-hand information in identifying possible amino acids, where mutations could be incorporated into MSTN gene of rohu carp including other carps for undertaking further in vivo studies.

Myostatin inhibitory region of fish (Paralichthys olivaceus) myostatin-1 propeptide

Myostatin (MSTN) is a potent negative regulator of skeletal muscle growth, and its activity is suppressed by MSTN propeptide (MSTNpro), the N-terminal part of MSTN precursor cleaved during post-translational MSTN processing. The current study examined which region of flatfish (Paralichthys olivaceus) MSTN-1 propeptide (MSTN1pro) is critical for MSTN inhibition. Six different truncated forms of MSTN1pro containing N-terminal maltose binding protein (MBP) as a fusion partner were expressed in Escherichia coli, and partially purified by an affinity chromatography for MSTN-inhibitory activity examination. Peptides covering different regions of flatfish MSTN1pro were also synthesized for MSTN-inhibitory activity examination. A MBP-fused MSTN1pro region consisting of residues 45-100 had the same MSTN-inhibitory potency as the full sequence flatfish MSTN1pro (residues 23-265), indicating that the region of flatfish MSTN1pro consisting of residues 45-100 is sufficient to maintain the full MSTN-inhibitory capacity. A MBP-fused MSTN1pro region consisting of residues 45-80 (Pro45-80) also showed MSTN-inhibitory activity with a lower potency, and the Pro45-80 demonstrated its MSTN binding capacity in a pull-down assay, indicating that the MSTN-inhibitory capacity of Pro45-80 is due to its binding to MSTN. Flatfish MSTN1pro synthetic peptides covering residues 45-65, 45-70, and 45-80 demonstrated MSTN-inhibitory activities, but not the synthetic peptide covering residues 45-54, indicating that residues 45-65 of flatfish MSTN1pro are essential for MSTN inhibition. In conclusion, current study show that like the mammalian MSTNpro, the MSTN-inhibitory region of flatfish MSTN1pro resides near its N-terminus, and imply that smaller sizes of MSTNpro can be effectively used in various applications designed for MSTN inhibition.

TALENs-mediated gene disruption of myostatin produces a larger phenotype of medaka with an apparently compromised immune system

Although myostatin, a suppressor of skeletal muscle development and growth, has been well studied in mammals, its function in fish remains unclear. In this study, we used a popular genome editing tool with high efficiency and target specificity (TALENs; transcription activator-like effector nucleases) to mutate the genome sequence of myostatin (MSTN) in medaka (Oryzias latipes). After the TALEN pair targeting OlMyostatin was injected into fertilized medaka eggs, mutant G0 fish carrying different TALENs-induced frameshifts in the OlMSTN coding sequence were mated together in order to transmit the mutant sequences to the F1 generation. Two F1 mutants with frameshifted myostatin alleles were then mated to produce the F2 generation, and these F2 OlMSTN null (MSTN(-/-)) medaka were evaluated for growth performance. The F2 fish showed significantly increased body length and weight compared to the wild type fish at the juvenile and post-juvenile stages. At the post-juvenile stage, the average body weight of the MSTN(-/-) medaka was ∼25% greater than the wild type. However, we also found that when the F3 generation were challenged with red spotted grouper nervous necrosis virus (RGNNV), the expression levels of the interferon-stimulated genes were lower than in the wild type, and the virus copy number was maintained at a high level. We therefore conclude that although the MSTN(-/-) medaka had a larger phenotype, their immune system appeared to be at least partially suppressed or undeveloped.

Depletion of Myostatin b Promotes Somatic Growth and Lipid Metabolism in Zebrafish

Myostatin (MSTN) is a negative regulator of myogenesis in vertebrates. Depletion of mstn resulted in elevated muscle growth in several animal species. However, the report on the complete ablation of mstn in teleost fish has not yet become available. In this study, two independent mstnb-deficient mutant lines in zebrafish were generated with the TALENs technique. In the mstnb-deficient zebrafish, enhanced muscle growth with muscle fiber hyperplasia was achieved. Beginning at the adult stage (80 days postfertilization), the mstnb-deficient zebrafish exhibited increased circumferences and body weights compared with the wild-type sibling control fish. Although the overall total lipid/body weight ratios remained similar between the mstnb-deficient zebrafish and the control fish, the distribution of lipids was altered. The size of the visceral adipose tissues became smaller while more lipids accumulated in skeletal muscle in the mstnb-deficient zebrafish than in the wild-type control fish. Based on the transcriptional expression profiles, our results revealed that lipid metabolism, including lipolysis and lipogenesis processes, was highly activated in the mstnb-deficient zebrafish, which indicated the transition of energy metabolism from protein-dependent to lipid-dependent in mstnb-deficient zebrafish. Our mstnb-deficient model could be valuable in understanding not only the growth trait regulation in teleosts but also the mechanisms of teleost energy metabolism.

Expression of myostatin in the spotted rose snapper Lutjanus guttatus during larval and juvenile development under cultured conditions

In this study, the developmental expression pattern of myostatin (mstn) in the spotted rose snapper Lutjanus guttatus under culture conditions is presented. The full coding sequence of mstn from L. guttatus was isolated from muscle tissue, obtaining 1134 nucleotides which encode a peptide of 377 amino acids. The phylogenetic analysis indicated that this sequence corresponds to mstn-1. mstn expression was detected in embryonic stages, and maintained at low levels until 28 days post-hatch, when it showed a significant increase, coinciding with the onset of metamorphosis. After that, expression was fluctuating, coinciding probably with periods of rapid and slow muscle growth or individual growth rates. mstn expression was also analysed by body mass with higher levels detected in smaller animals, irrespective of age. mstn was also expressed in other tissues from L. guttatus, presenting higher levels in brain, eye and gill. In brain for instance, two variants of mstn were isolated, both coding sequences were identical to muscle, except that one of them contained a 75 nucleotide deletion in exon 1, maintaining the reading frame but deleting two conserved cysteine residues. Phylogenetic analysis indicated that this brain variant was also mstn-1. The function of this variant is not clear and needs further investigation. These results indicate that mstn-1 participates in different physiological processes other than muscle growth in fishes.

Two myostatin genes exhibit divergent and conserved functions in grass carp (Ctenopharyngodon idellus)

Myostatin (MSTN) is an important negative regulator of myogenesis, which inhibits myoblast proliferation and differentiation. Here, we report the isolation and characterization of two mstn genes in grass carp (Ctenopharyngodon idellus). Grass carp mstn-1 and mstn-2 cDNAs are highly divergent, sharing a relatively low amino acid sequence identity of 66%. In adult fish, both orthologs are expressed in numerous tissues and they are differentially regulated during a fasting/refeeding treatments. During embryogenesis, the mRNA levels of both mstn-1 and -2 were upregulated significantly at the beginning of somitogenesis, and maintained at high levels until hatching. Using in situ hybridization, grass carp mstn-1 mRNA was found to ubiquitously express at 12hpf, with strong signals in the notochord, and in the eyes, brain and tailbud at 24hpf, and in brain and notochord at 36hpf. In comparison, the mstn-2 mRNA can be detected in the eyes, brain and notochord at 24hpf, and in the notochord and hindbrain at 36hpf. Further overexpression of mstn-1 mRNA caused a strongly ventralized phenotype by inhibiting dorsal tissue development, while injection of mstn-2 mRNA resulted in obvious embryonic abnormalities in grass carp. These results provide some new insights into the functional conservation and divergence of mstn genes in teleost species.

cDNA structure and the effect of fasting on myostatin expression in walking catfish (Clarias macrocephalus, Günther 1864)

We cloned and sequenced the myostatin (MSTN) gene of walking catfish and characterized its expression under different conditions. The full cDNA sequence of MSTN was 1,784 bp, containing an open reading frame of 1,191 bp, which encoded 396 amino acids. The deduced MSTN sequence contained functional sites similar to other members of TGF-β superfamily, including the proteolytic processing site and nine conserved cysteines in the C-terminal. Walking catfish MSTN mRNA was strongly expressed in skeletal muscle and brain tissues, consistent with the expression profiles of MSTN-1 isoform in other teleosts. Temporal expression analysis revealed that the MSTN was expressed at the highest levels in 1-week-old larvae and adults, but was lowest in early juveniles. A fasting-re-feeding experiment was used to evaluate the effects of starvation on growth and MSTN expression in juvenile walking catfish for 28 days. MSTN transcript levels increased significantly (threefold) after 7 days of fasting (P < 0.05) compared with the fed control. Subsequently, MSTN expression levels decreased 1.6-fold when fasting was extended to 14 days. Although re-feeding decreased the MSTN expression relative to the levels of the fed control, the period was not long enough for growth recovery of the juveniles. Our results supported a role of MSTN as a negative regulator of muscle growth and, possibly, a role in energy conservation in fish.

Swimming-induced exercise promotes hypertrophy and vascularization of fast skeletal muscle fibres and activation of myogenic and angiogenic transcriptional programs in adult zebrafish

BACKGROUND

The adult skeletal muscle is a plastic tissue with a remarkable ability to adapt to different levels of activity by altering its excitability, its contractile and metabolic phenotype and its mass. We previously reported on the potential of adult zebrafish as a tractable experimental model for exercise physiology, established its optimal swimming speed and showed that swimming-induced contractile activity potentiated somatic growth. Given that the underlying exercise-induced transcriptional mechanisms regulating muscle mass in vertebrates are not fully understood, here we investigated the cellular and molecular adaptive mechanisms taking place in fast skeletal muscle of adult zebrafish in response to swimming.

RESULTS

Fish were trained at low swimming speed (0.1 m/s; non-exercised) or at their optimal swimming speed (0.4 m/s; exercised). A significant increase in fibre cross-sectional area (1.290±88 vs. 1.665±106 μm2) and vascularization (298±23 vs. 458±38 capillaries/mm2) was found in exercised over non-exercised fish. Gene expression profiling by microarray analysis evidenced the activation of a series of complex transcriptional networks of extracellular and intracellular signaling molecules and pathways involved in the regulation of muscle mass (e.g. IGF-1/PI3K/mTOR, BMP, MSTN), myogenesis and satellite cell activation (e.g. PAX3, FGF, Notch, Wnt, MEF2, Hh, EphrinB2) and angiogenesis (e.g. VEGF, HIF, Notch, EphrinB2, KLF2), some of which had not been previously associated with exercise-induced contractile activity.

CONCLUSIONS

The results from the present study show that exercise-induced contractile activity in adult zebrafish promotes a coordinated adaptive response in fast muscle that leads to increased muscle mass by hypertrophy and increased vascularization by angiogenesis. We propose that these phenotypic adaptations are the result of extensive transcriptional changes induced by exercise. Analysis of the transcriptional networks that are activated in response to exercise in the adult zebrafish fast muscle resulted in the identification of key signaling pathways and factors for the regulation of skeletal muscle mass, myogenesis and angiogenesis that have been remarkably conserved during evolution from fish to mammals. These results further support the validity of the adult zebrafish as an exercise model to decipher the complex molecular and cellular mechanisms governing skeletal muscle mass and function in vertebrates.

Analyzing cold tolerance mechanism in transgenic zebrafish (Danio rerio)

Low temperatures may cause severe growth inhibition and mortality in fish. In order to understand the mechanism of cold tolerance, a transgenic zebrafish Tg (smyd1:m3ck) model was established to study the effect of energy homeostasis during cold stress. The muscle-specific promoter Smyd1 was used to express the carp muscle form III of creatine kinase (M3-CK), which maintained enzymatic activity at a relatively low temperature, in zebrafish skeletal muscle. In situ hybridization showed that M3-CK was expressed strongly in the skeletal muscle. When exposed to 13 °C, Tg (smyd1:m3ck) fish maintained their swimming behavior, while the wild-type could not. Energy measurements showed that the concentration of ATP increased in Tg (smyd1:m3ck) versus wild-type fish at 28 °C. After 2 h at 13 °C, ATP concentrations were 2.16-fold higher in Tg (smyd1:m3ck) than in wild-type (P<0.05). At 13 °C, the ATP concentration in Tg (smyd1:m3ck) fish and wild-type fish was 63.3% and 20.0%, respectively, of that in wild-type fish at 28 °C. Microarray analysis revealed differential expression of 1249 transcripts in Tg (smyd1:m3ck) versus wild-type fish under cold stress. Biological processes that were significantly overrepresented in this group included circadian rhythm, energy metabolism, lipid transport, and metabolism. These results are clues to understanding the mechanisms underlying temperature acclimation in fish.

High-fat diet reduces local myostatin-1 paralog expression and alters skeletal muscle lipid content in rainbow trout, Oncorhynchus mykiss

Muscle growth is an energetically demanding process that is reliant on intramuscular fatty acid depots in most fishes. The complex mechanisms regulating this growth and lipid metabolism are of great interest for human health and aquaculture applications. It is well established that the skeletal muscle chalone, myostatin, plays a role in lipid metabolism and adipogenesis in mammals; however, this function has not been fully assessed in fishes. We therefore examined the interaction between dietary lipid levels and myostatin expression in rainbow trout (Oncorhynchus mykiss). Five weeks of high-fat diet (HFD; 25 % lipid) intake increased white muscle lipid content and decreased circulating glucose levels and hepatosomatic index when compared to low-fat diet (LFD; 10 % lipid) intake. In addition, HFD intake reduced myostatin-1a and myostatin-1b expression in white muscle and myostatin-1b expression in brain tissue. Characterization of the myostatin-1a, myostatin-1b, and myostatin-2a promoters revealed putative binding sites for a subset of transcription factors associated with lipid metabolism. Taken together, these data suggest that HFD may regulate myostatin expression through cis-regulatory elements sensitive to increased lipid intake. Further, these findings provide a framework for future investigations of mechanisms describing the relationships between myostatin and lipid metabolism in fish.