A post-transcriptional mechanism regulates calpastatin expression in bovine skeletal muscle

The objective of this study was to investigate whether single nucleotide polymorphisms (SNP) in the calpain 1 (CAPN1), calpain 3 (CAPN3) and calpastatin (CAST) genes, which have been shown to be associated with shear force and tenderness differences in the skeletal muscle of cattle, contribute to phenotypic variation in muscle tenderness by modulating the transcriptional activity of their respective gene. The mRNA expression of the calpain and CAST genes was assessed in the longissimus lumborum muscle (LLM) of cattle from two herds located in distinct production zones on the east (New South Wales, NSW) and west (Western Australia, WA) of Australia. The cattle in the herds were mainly Brahman cattle (Bos indicus) with smaller populations of Angus cattle (Bos taurus). There were 191 steers in the WA herd and 107 steers and 106 heifers in the NSW herd. These herds were established by choosing cattle from the diverse population which had different single nucleotide polymorphism (SNP) genotypes at the CAPN1, CAPN3 and CAST loci. Using quantitative reverse transcriptase polymerase chain reaction (qRT-PCR), the transcriptional activities of the CAPN1 and the CAST genes, but not the CAPN3 gene, were found to differ between favorable, positively associated with tenderness, and unfavorable, negatively associated with tenderness, allelic variants of these genes. These findings suggest that the muscle shear force and consumer taste panel differences in tenderness explained by the CAPN1 and CAST gene markers are a consequence of alterations in their mRNA levels, which may ultimately influence the protein activity of these genes, thereby altering the rate and(or) the extent of postmortem proteolysis in skeletal muscle. Of particular importance were the significantly lower type II and type III CAST 5' splice variant mRNA levels that were detected in the LLM muscle of Brahman and Angus cattle with 2 favourable alleles of the CAST:c.2832A > G polymorphism. Moreover, a reduction in the abundance of an alternative polyadenylated variant of the CAST transcript, terminated at the proximal polyadenylation site, provides a unique insight into the potential involvement of a post-transcriptional regulatory mechanism which may influence protein expression levels in bovine skeletal muscle.