Vaughn, Robert Neil (2013-02). Genetic Mechanisms that Contribute to Differences in Beef Tenderness Following Electrical Stimulation. Doctoral Dissertation.
Tenderness is a key issue for consumers that is influenced by many environmental and genetic factors. Electrical stimulation (ES) is a postmortem treatment used to increase tenderness and reduce variation between carcasses within scientific treatment groups. The purpose of this study was to examine genetic factors that influence tenderness in response to ES. Samples were obtained from a crossbred Nellore-Angus herd produced in McGregor TX. Muscle samples were obtained immediately after slaughter, and those selected for this study were based on divergent response to ES. Tenderness was determined by objective Warner-Bratzler shear force measurements following 14 d of aging. A commercial cattle microarray was used to identify large sets of genes with significantly different gene expression between tenderness groups. These data were used to find significantly enriched genetic signaling pathways. A subset of genes based on expression and pathway analysis was selected for verification by realtime quantitative reverse transcriptase polymerase chain reaction (qRT-PCR). A subset of gene products was selected for western blot protein expression assays. In addition SNP haplotype blocks (hapblocks) were constructed that encompassed genes of interest to determine whether parent or breed of origin for these genes contributed to ES response. The ECM and closely related focal adhesion pathways were significantly enriched from the microarray assay. From this pathway a total of 40 genes was assayed by qRT-PCR. Of the assayed genes, many integrins were significantly upregulated in the group that responded well to electrical stimulation compared to the group that responded poorly. Through hapblock analysis, it was found that breed and parent of origin played a role in many production features including efficiency and growth rates. Breed of origin of integrin alpha-6 (ITGA6) could be linked to a 0.15 kg difference in ES residual tenderness values when inherited maternally (P = 0.03). The gene FN1 had a breed of origin effect, with a difference in ES residual tenderness of 0.23 kg for different paternally-inherited hapblocks. Additionally, ITGA6 protein expression was found to closely follow mRNA expression in a subset of animals chosen for western blot analysis. These results suggest that components of the ECM may be a novel area of research for improving tenderness that will benefit both producers and consumers.