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Discovery of a mammalian splice variant of myostatin that stimulates myogenesis.

ABSTRACT: Myostatin plays a fundamental role in regulating the size of skeletal muscles. To date, only a single myostatin gene and no splice variants have been identified in mammals. Here we describe the splicing of a cryptic intron that removes the coding sequence for the receptor binding moiety of sheep myostatin. The deduced polypeptide sequence of the myostatin splice variant (MSV) contains a 256 amino acid N-terminal domain, which is common to myostatin, and a unique C-terminus of 65 amino acids. Western immunoblotting demonstrated that MSV mRNA is translated into protein, which is present in skeletal muscles. To determine the biological role of MSV, we developed an MSV over-expressing C2C12 myoblast line and showed that it proliferated faster than that of the control line in association with an increased abundance of the CDK2/Cyclin E complex in the nucleus. Recombinant protein made for the novel C-terminus of MSV also stimulated myoblast proliferation and bound to myostatin with high affinity as determined by surface plasmon resonance assay. Therefore, we postulated that MSV functions as a binding protein and antagonist of myostatin. Consistent with our postulate, myostatin protein was co-immunoprecipitated from skeletal muscle extracts with an MSV-specific antibody. MSV over-expression in C2C12 myoblasts blocked myostatin-induced Smad2/3-dependent signaling, thereby confirming that MSV antagonizes the canonical myostatin pathway. Furthermore, MSV over-expression increased the abundance of MyoD, Myogenin and MRF4 proteins (P<0.05), which indicates that MSV stimulates myogenesis through the induction of myogenic regulatory factors. To help elucidate a possible role in vivo, we observed that MSV protein was more abundant during early post-natal muscle development, while myostatin remained unchanged, which suggests that MSV may promote the growth of skeletal muscles. We conclude that MSV represents a unique example of intra-genic regulation in which a splice variant directly antagonizes the biological activity of the canonical gene product.

SUBMITTER: Jeanplong F

PROVIDER: S-EPMC3846833 | biostudies-literature | 2013

REPOSITORIES: biostudies-literature

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Discovery of a mammalian splice variant of myostatin that stimulates myogenesis.

Jeanplong Ferenc F Falconer Shelley J SJ Oldham Jenny M JM Thomas Mark M Gray Tarra S TS Hennebry Alex A Matthews Kenneth G KG Kemp Frederick C FC Patel Ketan K Berry Carole C Nicholas Gina G McMahon Christopher D CD

PloS one 20131202 12

Myostatin plays a fundamental role in regulating the size of skeletal muscles. To date, only a single myostatin gene and no splice variants have been identified in mammals. Here we describe the splicing of a cryptic intron that removes the coding sequence for the receptor binding moiety of sheep myostatin. The deduced polypeptide sequence of the myostatin splice variant (MSV) contains a 256 amino acid N-terminal domain, which is common to myostatin, and a unique C-terminus of 65 amino acids. Wes ...[more]

PMID: 24312578

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Project description:ABSTRACT Stimulating the commitment of implanted dystrophin+ muscle derived stem cells (MDSC) into myogenic, as opposed to lipofibrogenic, lineages is a promising therapeutic strategy for Duchenne muscular dystrophy (DMD). To examine whether counteracting myostatin, a negative regulator of muscle mass and a pro-lipofibrotic factor, would help this process, we compared the in vitro myogenic and fibrogenic capacity of MDSC from wild type (WT), myostatin knockout (Mst KO), and mdx (DMD model) (mdx) young mice under various modulators, the expression of key stem cell and myogenic genes, and the capacity of these MDSC to repair the injured gastrocnemius in aged mdx mice with exacerbated lipofibrosis. Surprisingly, the potent in vitro myotube formation by WT MDSC was refractory to modulators of myostatin expression or activity, and the Mst KO and mdx MDSC failed to form myotubes under any condition, despite all MDSC expressed Oct-4 and various stem cell genes and differentiated into other lineages. The genetic inactivation of myostatin or dystrophin in MDSC was associated with silencing of critical genes for early myogenesis (Actc1, Acta1, and MyoD). WT MDSC implanted into the injured gastrocnemius of old mdx mice significantly improved myofiber repair and reduced fat deposition and, to a lesser extent, fibrosis. In contrast to their in vitro behavior, Mst KO MDSC in vivo also significantly improved myofiber repair, but had no significant effects on lipofibrotic degeneration. In conclusion, while WT MDSC are considerably myogenic in culture and stimulate muscle repair after injury in the aged mdx mouse, myostatin genetic inactivation blocks myotube formation in vitro but the myogenic capacity is recovered in vivo under the influence of the host tissue environment, presumably by reactivation of key genes originally silenced in the Mst KO MDSC. Key words: dystrophin, mdx mouse, Duchenne, fibrosis, dystrophy One sample each of mouse wild type (WT), myostatin knockout (KO), muscular dystrophy model mdx, and the transgenic OCT4 promoter plus reporter were grown, RNA was isolated, and subjected to the SABiosciences mouse stem cell oligo array.

Dataset Information

Discovery of a mammalian splice variant of myostatin that stimulates myogenesis.

Publications

Discovery of a mammalian splice variant of myostatin that stimulates myogenesis.

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