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

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.

cDNA sequence and protein bioinformatics analyses of MSTN in African catfish (Clarias gariepinus)

Myostatin, also known as growth differentiation factor 8, has been identified as a potent negative regulator of skeletal muscle growth. The purpose of this study was to characterize and predict function of the myostatin gene of the African catfish (Cg-MSTN). Expression of Cg-MSTN was determined at three growth stages to establish the relationship between the levels of MSTN transcript and skeletal muscle growth. The partial cDNA sequence of Cg-MSTN was cloned by using published information from its congener walking catfish (Cm-MSTN). The Cg-MSTN was 1194 bp in length encoding a protein of 397 amino acids. The deduced MSTN sequence exhibited key functional sites similar to those of other members of the TGF-β superfamily, especially, the proteolytic processing site (RXXR motif) and nine conserved cysteines at the C-terminal. Expression of MSTN appeared to be correlated with muscle development and growth of African catfish. Protein bioinformatics revealed that the primary sequence of Cg-MSTN shared 98 % sequence identity with that of walking catfish Cm-MSTN with only two different residues, [Formula: see text]. and [Formula: see text]. The proposed model of Cg-MSTN revealed the key point mutation [Formula: see text] causing a 7.35 Å shorter distance between the N- and C-lobes and an approximately 11° narrow angle than those of Cm-MSTN. The substitution of a proline residue near the proteolytic processing site which altered the structure of myostatin may play a critical role in reducing proteolytic activity of this protein in African catfish.

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.

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.