Characterization and functional analysis of the 5′ flanking region of Sparus aurata myostatin-1 gene

Myocyte enhancer factor 2 upregulates expression of myostatin promoter in Yesso scallop, Patinopecten yessoensis

Myostatin (MSTN) plays an important role in muscle development in animals, especially for mammals and fishes. However, little information has been reported on the regulation of MSTN in marine invertebrates, such as bivalves. In the present study, we cloned the MSTN promoter sequence of Yesso scallop Patinopecten yessoensis, identifying 4 transcription start sites, eleven TATA boxes and one E-box. Additionally, transcription factor binding sites, including myocyte enhancer factor 2 (MEF2) and POU homeodomain protein, were identified. The interaction between the MSTN promoter and MEF2 was analyzed to reveal the transcriptional activity of different fragment sizes of promoters through the dual-luciferase reporter assays. The highest transcriptional activity was found in recombinant plasmids with the most MEF2 binding sites, indicating that this transcription factor upregulates MSTN in Yesso scallop. This study provides new insight into the regulation of muscle growth and development in this species.

Salinity, Temperature and Ammonia Acute Stress Response in Seabream (Sparus aurata) Juveniles: A Multidisciplinary Study

The present study aimed to investigate the acute response of gilthead seabream (Sparus aurata) juveniles exposed to temperature, salinity and ammonia stress. Radioimmunoassay was used to evaluate cortisol levels, whereas insulin-like growth factors (igf1 and igf2), myostatin (mstn), heat-shock protein 70 (hsp70) and glucocorticoid receptor (gr) gene expression was assessed trough Real-Time PCR. The presence and localization of IGF-I and HSP70 were investigated by immunohistochemistry. In all the stress conditions, a significant increase in cortisol levels was observed reaching higher values in the thermic and chemical stress groups. Regarding fish growth markers, igf1 gene expression was significantly higher only in fish subjected to heat shock stress while, at 60 min, igf2 gene expression was significantly lower in all the stressed groups. Temperature and ammonia changes resulted in a higher mstn gene expression. Molecular analyses on stress response evidenced a time dependent increase in hsp70 gene expression, that was significantly higher at 60 min in fish exposed to heat shock and chemical stress. Furthermore, the same experimental groups were characterized by a significantly higher gr gene expression respect to the control one. Immunostaining for IGF-I and HSP70 antibodies was observed in skin, gills, liver, and digestive system of gilthead seabream juveniles.

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.

Glucocorticoid-induced CREB activation and myostatin expression in C2C12 myotubes involves phosphodiesterase-3/4 signaling

Muscle atrophy in metabolic conditions like chronic kidney disease (CKD) and diabetes are associated with glucocorticoid production, dysfunctional insulin/Akt/FoxO3 signaling and increased myostatin expression. We recently found that CREB, a transcription factor proposed to regulate myostatin expression, is highly phosphorylated in some wasting conditions. Based on a novel Akt-PDE3/4 signaling paradigm, we hypothesized that reduced Akt signaling contributes to CREB activation and myostatin expression. C2C12 myotubes were incubated with dexamethasone (Dex), an atrophy-inducing synthetic glucocorticoid. Akt/CREB signaling and myostatin expression were evaluated by immunoblot and qPCR analyses. Inhibitors of Akt, phosphodiesterase (PDE)-3/4, and protein kinase A (PKA) signaling were used to test our hypothesis. Incubating myotubes with Dex for 3-24 h inhibited Akt phosphorylation and enhanced CREB phosphorylation as well as myostatin mRNA and protein. Inhibition of PI3K/Akt signaling with LY294002 similarly increased CREB phosphorylation. Isobutyl-methylxanthine (IBMX, a pan PDE inhibitor), milrinone (PDE3 inhibitor) and rolipram (PDE4 inhibitor) augmented CREB phosphorylation and myostatin expression. Inhibition of protein kinase A by PKI reverted Dex- or IBMX-induced CREB phosphorylation and myostatin expression. Our study provides evidence supporting a newly identified mechanism by which a glucocorticoid-related reduction in Akt signaling contributes to myostatin expression via CREB activation.

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.

A comparative examination of cortisol effects on muscle myostatin and HSP90 gene expression in salmonids

Cortisol, the primary corticosteroid in teleost fishes, is released in response to stressors to elicit local functions, however little is understood regarding muscle-specific responses to cortisol in these fishes. In mammals, glucocorticoids strongly regulate the muscle growth inhibitor, myostatin, via glucocorticoid response elements (GREs) leading to muscle atrophy. Bioinformatics methods suggest that this regulatory mechanism is conserved among vertebrates, however recent evidence suggests some fishes exhibit divergent regulation. Therefore, the aim of this study was to evaluate the conserved actions of cortisol on myostatin and hsp90 expression to determine if variations in cortisol interactions have emerged in salmonid species. Representative salmonids; Chinook salmon (Oncorhynchus tshawytscha), cutthroat trout (Oncorhynchus clarki), brook trout (Salvelinus fontinalis), and Atlantic salmon (Salmo salar); were injected intraperitoneally with a cortisol implant (50μg/g body weight) and muscle gene expression was quantified after 48h. Plasma glucose and cortisol levels were significantly elevated by cortisol in all species, demonstrating physiological effectiveness of the treatment. HSP90 mRNA levels were elevated by cortisol in brook trout, Chinook salmon, and Atlantic salmon, but were decreased in cutthroat trout. Myostatin mRNA levels were affected in a species, tissue (muscle type), and paralog specific manner. Cortisol treatment increased myostatin expression in brook trout (Salvelinus) and Atlantic salmon (Salmo), but not in Chinook salmon (Oncorhynchus) or cutthroat trout (Oncorhynchus). Interestingly, the VC alone increased myostatin mRNA expression in Chinook and Atlantic salmon, while the addition of cortisol blocked the response. Taken together, these results suggest that cortisol affects muscle-specific gene expression in species-specific manners, with unique Oncorhynchus-specific divergence observed, that are not predictive solely based upon mammalian stress responses.

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.

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.

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.

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.

The effects of exogenous cortisol on myostatin transcription in rainbow trout, Oncorhynchus mykiss

Glucocorticoids (GCs) strongly regulate myostatin expression in mammals via glucocorticoid response elements (GREs), and bioinformatics methods suggest that this regulatory mechanism is conserved among many vertebrates. However, the multiple myostatin genes found in some fishes may be an exception. In silico promoter analyses of the three putative rainbow trout (Oncorhynchus mykiss) myostatin promoters have failed to identify putative GREs, suggesting a divergence in myostatin function. Therefore, we hypothesized that myostatin mRNA expression is not regulated by glucocorticoids in rainbow trout. In this study, both juvenile rainbow trout and primary trout myoblasts were treated with cortisol to examine the effects on myostatin mRNA expression. Results suggest that exogenous cortisol does not regulate myostatin-1a and -1b expression in vivo, as myostatin mRNA levels were not significantly affected by cortisol treatment in either red or white muscle tissue. In red muscle, myostatin-2a levels were significantly elevated in the cortisol treatment group relative to the control, but not the vehicle control, at both 12 h and 24 h post-injection. As such, it is unclear if cortisol was acting alone or in combination with the vehicle. Cortisol increased myostatin-1b expression in a dose-dependent manner in vitro. Further work is needed to determine if this response is the direct result of cortisol acting on the myostatin-1b promoter or through an alternative mechanism. These results suggest that regulation of myostatin by cortisol may not be as highly conserved as previously thought and support previous work that describes potential functional divergence of the multiple myostatin genes in fishes.

Revisiting the paradigm of myostatin in vertebrates: insights from fishes

In the last decade, myostatin (MSTN), a member of the TGFβ superfamily, has emerged as a strong inhibitor of muscle growth in mammals. In fish many studies reveal a strong conservation of mstn gene organization, sequence, and protein structures. Because of ancient genome duplication, teleostei may have retained two copies of mstn genes and even up to four copies in salmonids due to additional genome duplication event. In sharp contrast to mammals, the different fish mstn orthologs are widely expressed with a tissue-specific expression pattern. Quantification of mstn mRNA in fish under different physiological conditions, demonstrates that endogenous expression of mstn paralogs is rarely related to fish muscle growth rate. In addition, attempts to inhibit MSTN activity did not consistently enhance muscle growth as in mammals. In vitro, MSTN stimulates myotube atrophy and inhibits proliferation but not differentiation of myogenic cells as in mammals. In conclusion, given the strong mstn expression non-muscle tissues of fish, we propose a new hypothesis stating that fish MSTN functions as a general inhibitors of cell proliferation and cell growth to control tissue mass but is not specialized into a strong muscle regulator.

The cAMP response element binding protein (CREB) is activated by insulin-like growth factor-1 (IGF-1) and regulates myostatin gene expression in skeletal myoblast

Myostatin, a member of the Transforming Growth Factor beta (TGF-β) superfamily, plays an important role as a negative regulator of skeletal muscle growth and differentiation. We have previously reported that IGF-1 induces a transient myostatin mRNA expression, through the activation of the Nuclear Factor of Activated T cells (NFAT) in an IP3/calcium-dependent manner. Here we examined the activation of CREB transcription factor as downstream targets of IGF-1 during myoblast differentiation and its role as a regulator of myostatin gene expression. In cultured skeletal myoblast, IGF-1 induced the phosphorylation and transcriptional activation of CREB via IGF-1 Receptor/Phosphatidylinositol 3-Kinase (PI3K)/Phospholipase C gamma (PLC γ), signaling pathways. Also, IGF-1 induced calcium-dependent molecules such as Calmodulin Kinase II (CaMK II), Extracellular signal-regulated Kinases (ERK), Protein Kinase C (PKC). Additionally, we examined myostatin mRNA levels and myostatin promoter activity in differentiated myoblasts stimulated with IGF-1. We found a significant increase in mRNA contents of myostatin and its reporter activity after treatment with IGF-1. The expression of myostatin in differentiated myoblast was downregulated by the transfection of siRNA-CREB and by pharmacological inhibitors of the signaling pathways involved in CREB activation. By using pharmacological and genetic approaches together these data demonstrate that IGF-1 regulates the myostatin gene expression via CREB transcription factor during muscle cell differentiation.

Genomic cloning and promoter functional analysis of myostatin-2 in shi drum, Umbrina cirrosa: conservation of muscle-specific promoter activity

Myostatin (MSTN) is a member of the transforming growth factor-ß superfamily, known as a negative regulator of skeletal muscle development and growth in mammals. In contrast to mammals, fish possess at least two paralogs of MSTN: MSTN-1 and MSTN-2. Here we describe the cloning and sequence analysis of spliced and precursor (unspliced) transcripts as well as the 5' flanking region of MSTN-2 from the marine fish Umbrina cirrosa (ucMSTN-2). In silico analysis revealed numerous putative cis regulatory elements including several E-boxes known as binding sites to myogenic transcription factors. Transient transfection experiments using non-muscle and muscle cell lines showed high transcriptional activity in muscle cells and in differentiated neural cells, in accordance with our previous findings in MSTN-2 promoter from Sparus aurata. Comparative informatics analysis of MSTN-2 from several fish species revealed high conservation of the predicted amino acid sequence as well as the gene structure (exon length) although intron length varied between species. The proximal promoter of MSTN-2 gene was found to be conserved among Perciforms. In conclusion, this study reinforces our conclusion that MSTN-2 promoter is a very strong promoter, especially in muscle cells. In addition, we show that the MSTN-2 gene structure is highly conserved among fishes as is the predicted amino acid sequence of the peptide.

Structural and functional analysis of myostatin-2 promoter alleles from the marine fish Sparus aurata: evidence for strong muscle-specific promoter activity and post-transcriptional regulation

Myostatin (MSTN) is a negative regulator of skeletal muscle growth. In contrast to mammals, fish possess at least two paralogs of MSTN: MSTN-1 and MSTN-2. In this study, we analyzed the structural-functional features of the four variants of Sparus aurata MSTN-2 5'-flanking region: saMSTN-2a, saMSTN-2as, saMSTN-2b and saMSTN-2c. In silico analysis revealed numerous putative cis regulatory elements including several E-boxes known as binding sites to myogenic transcription factors. Transient transfection experiments using non-muscle and muscle cell lines showed surprisingly high transcriptional activity in muscle cells, suggesting the presence of regulatory elements unique to differentiated myotubes. These observations were confirmed by in situ intramuscular injections of promoter DNA followed by reporter gene assays. Moreover, high promoter activity was found in differentiated neural cell, in agreement with MSTN-2 expression in brain. Progressive 5'-deletion analysis, using reporter gene assays, showed that the core promoter is located within the first -127 bp upstream of the ATG, and suggested the presence of regulatory elements that either repress or induce transcriptional activity. Transient transgenic zebrafish provided evidence for saMSTN-2 promoter ability to direct GFP expression to myofibers. Finally, our data shows that although no mature saMSTN-2 mRNA is observed in muscle; unspliced forms accumulate, confirming high level of transcription. In conclusion, our study shows for the first time that MSTN-2 promoter is a very robust promoter, especially in muscle cells.

Dexamethasone-induced skeletal muscle atrophy was associated with upregulation of myostatin promoter activity

Some recent studies showed that the glucocorticoid-induced muscle atrophy was associated with myostatin, a negative regulator of skeletal muscle. In this study, two experiments were performed to investigate the relationship between the glucocorticoid-induced ultrastructural changes in skeletal muscle and the myostatin gene expression, and to examine in vivo whether the glucocorticoid-induced upregulation of myostatin gene expression is associated with the myostatin promoter activity. In the first experiment, the Kun-Ming mice with similar body weights were treated with high-dose dexamethasone. The results showed that high-dose dexamethasone caused myofibrillar disorganization or degradation and mitochondrial swelling or vacuolization, which were accompanied with the upregulation of myostatin expression. In the second experiment, the mice were treated with the wild-type or GRE (glucocorticoid response elements)-mutant myostatin promoter vector and high-dose dexamethasone alone or together with RU486. The results showed that the mutation of GRE motif resulted in the obvious decrease of the myostatin promoter activity, the high-dose dexamethasone promoted significantly the activity of the wild-type myostatin promoter but did not affect the activity of the GRE-mutant myostatin promoter, and RU486 inhibited the effect of dexamethasone on the wild-type myostatin promoter activity. Taken together, these results suggested that the dexamethasone-induced changes in ultrastructure of skeletal muscle were associated with the upregulation of myostatin gene expression and the upregulation was partly attributed to the binding of glucocorticoid receptor to GRE motifs along myostatin promoter.

Functional analysis of pig myostatin gene promoter with some adipogenesis- and myogenesis-related factors

Myostatin (MSTN) is primarily expressed in muscle and plays an important role in muscle and fat development in pigs. However, there is little information about the regulation of pig MSTN. In order to elucidate whether pig MSTN could be regulated by muscle- and fat-related factors, the porcine MSTN promoter was amplified and cloned into pGL3-basic vector, and transfected into cells to analyze the transcriptional activity of promoter with muscle- and fat-related factors through dual-luciferase reporter assays. 5'-deletion expression showed that there was a negative-regulatory region located between nucleotides -1519 and -1236 bp, and there were some positive-regulatory regions located between -1236 and -568 bp. The longest fragment (1.7 kb) was cotransfected with muscle-related transcription factor myogenic differentiation 1 (MyoD), resulting in promoter transcriptional activity upregulation. The fragment was treated by the adipogenic agents (DIM) including dexamethasone, insulin, and isobutyl-1-methylxanthine (IBMX). We found that MSTN promoter transcriptional activity can be regulated by IBMX, but not by DIM. CCAAT/enhancer binding protein (C/EBP) α and C/EBPβ, two proteins which are induced by DIM during adipogenesis were cotransfected with the 1.7-kb fragment, respectively, resulting in promoter transcriptional activity downregulation. Treating the fragment with rosiglitazone which induce the expression of peroxisome proliferator-activated receptor γ (PPARγ), resulting in promoter transcriptional activity upregulation. Cotransfection experiments confirmed this result. Taken together, we showed that porcine MSTN could be upregulated by IBMX, MyoD, and PPARγ but downregulated by C/EBPα and C/EBPβ.

Organization and functional analysis of the 5' flanking regions of myostatin-1 and 2 genes from Larimichthys crocea

Myostatin (MSTN) is a negative regulator of skeletal muscle growth and development. There are two types of MSTNs in fish, but little is known about their gene regulation. Here, the 5' flanking fragments of 1029 bp from MSTN-1 and 643 bp from MSTN-2 were cloned, sequenced, and analyzed in Larimichthys crocea. Both fragments contained CAAT box and several putative cis-regulatory elements. However, putative TATA box, MyoD, MEF3, SP1, USF, and GH-CSE sites were identified only in the L. crocea MSTN-1 (lcMSTN-1) promoter. Transcriptional activities of four fragments (1013, 841, 514, and 261 bp) truncated from lcMSTN-1 upstream region and two fragments (643 and 296 bp) from lcMSTN-2 upstream region were examined in vitro, using transient transfection in CIK and L6 cells. In CIK cells, the promoter activity correlated positively with the length of truncated fragments in both MSTN-1 and 2. The lcMSTN-2 promoter showed a higher activity than lcMSTN-1 in the corresponding region, which was consistent with MSTN gene expression in vivo. In L6 cells, lcMSTN-2 upstream showed an extremely high luciferase activity. These data indicated that both cloned 5' flanking sequences contained functional promoters, and that transcription regulation of lcMSTN-1 and 2 promoters was significantly different between mammalian and fish cells.

Myostatin-2 gene structure and polymorphism of the promoter and first intron in the marine fish Sparus aurata: evidence for DNA duplications and/or translocations

BACKGROUND

Myostatin (MSTN) is a member of the transforming growth factor-ß superfamily that functions as a negative regulator of skeletal muscle development and growth in mammals. Fish express at least two genes for MSTN: MSTN-1 and MSTN-2. To date, MSTN-2 promoters have been cloned only from salmonids and zebrafish.

RESULTS

Here we described the cloning and sequence analysis of MSTN-2 gene and its 5' flanking region in the marine fish Sparus aurata (saMSTN-2). We demonstrate the existence of three alleles of the promoter and three alleles of the first intron. Sequence comparison of the promoter region in the three alleles revealed that although the sequences of the first 1050 bp upstream of the translation start site are almost identical in the three alleles, a substantial sequence divergence is seen further upstream. Careful sequence analysis of the region upstream of the first 1050 bp in the three alleles identified several elements that appear to be repeated in some or all sequences, at different positions. This suggests that the promoter region of saMSTN-2 has been subjected to various chromosomal rearrangements during the course of evolution, reflecting either insertion or deletion events. Screening of several genomic DNA collections indicated differences in allele frequency, with allele 'b' being the most abundant, followed by allele 'c', whereas allele 'a' is relatively rare. Sequence analysis of saMSTN-2 gene also revealed polymorphism in the first intron, identifying three alleles. The length difference in alleles '1R' and '2R' of the first intron is due to the presence of one or two copies of a repeated block of approximately 150 bp, located at the 5' end of the first intron. The third allele, '4R', has an additional insertion of 323 bp located 116 bp upstream of the 3' end of the first intron. Analysis of several DNA collections showed that the '2R' allele is the most common, followed by the '4R' allele, whereas the '1R' allele is relatively rare. Progeny analysis of a full-sib family showed a Mendelian mode of inheritance of the two genetic loci. No clear association was found between the two genetic markers and growth rate.

CONCLUSION

These results show for the first time a substantial degree of polymorphism in both the promoter and first intron of MSTN-2 gene in a perciform fish species which points to chromosomal rearrangements that took place during evolution.