Genetic variation in the bovine myostatin gene and its effect on muscularity
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2010
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Melbourne Authors
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Melbourne School of Land and Environment, Agriculture and Food Systems
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PhD thesis
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O'Rourke, B. A. (2010). Genetic variation in the bovine myostatin gene and its effect on muscularity. PhD thesis, Melbourne School of Land and Environment, Agriculture and Food Systems, The University of Melbourne.
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© 2010 Dr. Brendon Andrew O'Rourke
Abstract
Retail beef yield (RBY) refers to the amount of saleable meat from an animal, and is an economically important trait for the beef industry. The gross components that determine RBY are skeletal muscle, bone and fat content:
Skeletal muscle is the most abundant tissue and has high economic value. The propensity to develop muscle mass is heritable and it is controlled by many genes. Genetic variation within these genes can influence differences in muscle mass.
The studies within this thesis, further investigated the effect of genetic variation in the myostatin (MSTN) gene on muscle mass in cattle. MSTN was selected as a candidate for further investigation because of its important role in muscle development. Previous studies have found loss-of-function mutations in MSTN that are responsible for extreme increases in muscle mass, known as double muscling, and a high level of genetic variability. The primary objective of this thesis was to determine if MSTN polymorphisms which have not been implicated in double muscling, are also contributing to variation in muscularity.
Genetic variation in bovine MSTN was examined in a sub-population of Angus cattle. Eighteen polymorphisms were identified and the haplotype diversity was inferred. From the phased haplotypes the extent of linkage disequilibrium between the polymorphisms was determined, which provided a tag SNP genotyping strategy using six MSTN polymorphisms.
Large cattle populations (Herds A to E) were genotyped at each of the tag SNP sites. Haplotypes were inferred from the genotypic data, and were then used to test associations with quantitative indices for muscularity. The results from Herd A used as the discovery population showed that haplotypes 2 and 7 had a moderate effect on eye muscle area relative to double muscling heterozygotes and haplotypes 8 and 9 had a small effect. Similar trends were observed for these haplotypes in the validation population compromising Herds B to E.
The effect of the MSTN haplotypes was also examined for other carcass, meat quality and feed efficiency traits. Significant associations were found for almost all traits examined, but their effects could not be proven as casual and requires further validation. Differences in gene expression between the MSTN haplotypes were also investigated to provide biological support for the quantitative associations. The data from this study did not provide convincing support for the quantitative associations, which may have been biased by measurements between assays, differences in splicing or because the differences in eye muscle area are not due to MSTN. The effect of the MSTN splice variant warrants further investigation since a favourable role has been demonstrated previously in sheep A historical perspective on recent selection pressure for double mutations has also been provided. The time to the most recent common ancestor was investigated for multiple MSTN mutations responsible for double muscling. The long regions of haplotype homozygosity that were found associated with the double muscling mutations indicate the time to the most recent common ancestor occurred is consistent with the first reports of double muscling approximately 200 years ago.
The studies within this thesis have further contributed to the elucidation of the biology of muscling. It has been demonstrated that other MSTN polymorphisms, not implicated in double muscling, are also contributing to variation in muscle mass. This knowledge will add value to current methods for estimating the genetic merit of beef cattle and may offer more practical genomic selection alternative to improve muscling in beef cattle.
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myostatin, muscle, genetics