The "speed gene" effect of myostatin arises in Thoroughbred horses due to a promoter proximal SINE insertion.
Authors: Rooney Mary F, Hill Emmeline W, Kelly Vincent P, Porter Richard K
Journal: PloS one
Summary
Myostatin, a potent inhibitor of muscle growth, has long been implicated in racing performance across Thoroughbreds, with two genetic variants in the MSTN gene previously linked to race distance aptitude; however, uncertainty remained about which variant was functionally responsible for the "speed gene" effect. Rooney and colleagues employed both population-level genetic analysis and in vitro myoblast studies to isolate the causal mechanism, discovering complete concordance between a single nucleotide polymorphism (SNP) in the first intron and a 227 base pair SINE transposable element insertion in the promoter region. Their findings demonstrate that only the SINE insertion functionally impairs myostatin transcription initiation and gene expression in skeletal muscle, whilst the SNP alone exerts no independent effect—a conclusion reinforced by direct mapping of transcription start sites in equine muscle tissue. For practitioners, this clarifies that genetic testing for racing distance aptitude should focus on the SINE insertion polymorphism specifically, as it directly modulates myostatin protein production and consequently influences the balance between aerobic capacity and muscle mass that distinguishes elite endurance versus sprint performers. Understanding this mechanistic basis may also have implications for selective breeding programmes and for interpreting genetic profiles when assessing individual horses' physiological potential across different racing distances.
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Practical Takeaways
- •Genetic testing for the SINE insertion polymorphism (not the SNP) could identify Thoroughbreds with genetic predisposition for sprint versus distance racing aptitude
- •Understanding the mechanistic basis of myostatin variants provides a foundation for future selective breeding decisions aimed at optimizing race distance suitability
- •This discovery clarifies which genetic marker is functionally responsible, enabling more accurate genomic predictions for Thoroughbred performance potential
Key Findings
- •The SINE insertion (not the SNP) in the myostatin promoter region is exclusively responsible for the 'speed gene' effect in Thoroughbreds
- •Complete concordance observed between the SNP and SINE insertion polymorphisms in Thoroughbred populations
- •In vitro assays demonstrated the SINE insertion adversely affects transcription initiation and myostatin protein production
- •Mapping of MSTN transcription start site confirmed anomalous transcription initiation occurs only in the presence of the SINE insertion