Disease relevance of GDF8

• In contrast, loss of MSTN activity in the dyW/dyW mouse model of laminin-deficient congenital muscular dystrophy, a much more severe and lethal disease model, does not improve all aspects of muscle pathology [1].
• Thus, we propose that the generalized muscular hyperplasia phenotype observed in animals that lack functional myostatin could be as a result of deregulated myoblast proliferation [2].
• Early loss of MSTN activity achieved either by monoclonal antibody administration or by gene deletion each improved muscle mass, regeneration, and reduced fibrosis in scgd-/- mice [1].
• Here we examined disease severity associated with myostatin (mstn-/-) deletion in mice nullizygous for delta-sarcoglycan (scgd-/-), a model of limb-girdle muscular dystrophy [1].
• Interestingly, studies have demonstrated some rescue effects of myostatin in muscular pathologies such as myopathies, providing a novel pharmacological strategy for treatment [3].

High impact information on GDF8

• Because targeted disruption of myostatin in mice results in a muscular phenotype very similar to that seen in double-muscled cattle, we have evaluated this gene as a candidate gene for double-muscling condition by cloning the bovine myostatin cDNA and examining the expression pattern and sequence of the gene in normal and double-muscled cattle [4].
• The autosomal recessive mh locus causing double-muscling condition in these cattle maps to bovine chromosome 2 within the same interval as myostatin, a member of the TGF-beta superfamily of genes [4].
• This deletion results in a frame-shift mutation that removes the portion of the Myostatin protein that is most highly conserved among TGF-beta family members and that is the portion targeted for disruption in the mouse study [4].
• Furthermore, we also observed that in myoblasts treated with myostatin protein, Rb was predominately present in the hypophosphorylated form [2].
• Myostatin, a member of the transforming growth factor-beta (TGF-beta) superfamily, has been shown to be a negative regulator of myogenesis [2].

Biological context of GDF8

• Myostatin, or growth and differentiation factor 8 (GDF8), has been identified as the factor causing a phenotype known as double muscling, in which a series of mutations render the gene inactive, and therefore, unable to regulate muscle fibre deposition [5].
• A number of recessive alleles in the bovine myostatin gene (GDF8, mapped to bovine chromosome 2 and apparently orthologous to the human 2q22 region) have been shown to be responsible for DM [6].
• Myostatin, a secreted growth factor, is a member of the TGF-beta superfamily and an inhibitor of myogenesis [7].
• Based on these results, we propose that myostatin auto-regulates its gene expression through a Smad7 dependent mechanism in myogenic cells [7].
• In the first exon of bovine myostatin, a single transcription initiation site is found at 133 bps from the translation start codon ATG [8].

Anatomical context of GDF8

• Consistent with these results, a decrease in Smad7 mRNA and concomitant increase in myostatin expression is seen in myotubes that express non functional myostatin [7].
• Myostatin belongs to the Transforming Growth Factor-beta (TGF-beta) superfamily and is expressed in developing and mature skeletal muscle [8].
• Myostatin was identified as the candidate gene whose expression may contribute to the observed changes in muscle development of these fetuses [9].
• Myostatin inhibits cell proliferation and protein synthesis in C2C12 muscle cells [10].
• After verification of the expression of cDNA constructs in a cell-free system and in transfected Chinese hamster ovary cells, the human recombinant protein was expressed as the full-length (375-amino acid) myostatin in Drosophila cells (Mst375D), or the 110-amino acid carboxy-terminal protein in Escherichia coli (Mst110EC) [10].

Associations of GDF8 with chemical compounds

• Piedmontese cattle are a heavy-muscled breed that express a mutated form of myostatin in which cysteine (313) is substituted with tyrosine [11].
• Single cysteine to tyrosine transition inactivates the growth inhibitory function of Piedmontese myostatin [11].
• Myostatin, a member of the transforming growth factor-beta superfamily, is a secreted growth factor that is proteolytically processed to give COOH-terminal mature myostatin and NH2-terminal latency-associated peptide in myoblasts [11].
• These results indicate that, in Piedmontese myostatin, substitution of cysteine with tyrosine results in the distortion of the "cystine knot" structure and a loss of biological activity of the myostatin [11].
• Use of inactive myostatin was profitable as long as the price for Select was at least 80% of the Choice price and the price for Standard at least 60% [12].

Regulatory relationships of GDF8

• We also observed that follistatin stimulates preadipocyte differentiation in the presence of myostatin [13].

Other interactions of GDF8

• During frostbite-induced muscle regeneration, gene expression for myostatin and 4 MRF; i.e., Myf5, MyoD, myogenin and MRF4, showed contrasting responses [14].
• Western analysis indicated that myostatin specifically up-regulated p21(Waf1, Cip1), a cyclin-dependent kinase inhibitor, and decreased the levels and activity of Cdk2 protein in myoblasts [2].
• This is the first time a direct relationship has been reported between GH, cortisol, and myostatin [15].

Analytical, diagnostic and therapeutic context of GDF8

• Northern blot analysis indicated that there are relatively higher levels of myostatin mRNA in the biceps femoris muscle of cattle that express a non- functional myostatin allele (Belgian Blue) as compared to normal cattle [7].
• Using quantitative RT-PCR we have analysed neonatal expression of myostatin gene [8].
• Fluorescence-activated cell sorting analysis revealed that myostatin prevented the progression of myoblasts from the G(1)- to S-phase of the cell cycle [2].
• PCR based detection of bovine myostatin Q204X mutation [16].
• We describe sequence analysis of the myostatin gene in ten beef breeds commonly used in the UK and show that the 11-bp deletion responsible for double-muscling in the Belgian Blue is also present in the South Devon cattle population [17].

References