Expression of PRKAG3 gene and possible association with glycogen content in cattle

The protein kinase, AMP-activated, γ3 non-catalytic subunit (PRKAG3) gene is a member of the 5'-AMP-activated protein kinase (AMPK) gene family. The AMPK is a heterotrimer consisting of a α catalytic subunit, and non-catalytic β and γ subunits. AMPK is an important energy-sensing enzyme that monitors cellular energy status. Mutations affecting the genes encoding the regulatory γ subunits have been shown to influence AMPK activity. In pig, mutations on the PRKAG3 gene affect meat quality by influencing muscle glycogen content. The PRKAG3 gene encodes the γ3 isoform of the regulatory γ subunit. This isoform is mainly expressed in white skeletal muscle, where it is the predominant γ isoform suggesting that it has a key role in this tissue. The bovine PRKAG3 gene, located on chromosome 2 (BTA2), harbours 14 exons spanning 6.8 kb on genomic DNA. We identified 36 SNPs, in both introns and exons of the gene, as well as alternative splicing sites at two positions of the gene. Multiple PRKAG3 transcripts have been identified that might encode a set of sub-isoforms of the γ3 subunit. A preliminary work has been done in order to find possible associations between specific polymorphisms and phenotypic traits. In this study, 100 Holstein animals were genotyped for 11 markers and 3 major haplotypes were identified (74%, 12% and 11.5%). Different phenotypic traits including meat characteristics (pH value, glycogen content, drip loss) were measured for these animals. We found a significant association (p < 0.05) between glycogen content and one polymorphism present on the PRKAG3 gene. We also identified, in another set of animals, a polymorphism influencing the expression level of the gene in a glycolytic skeletal muscle. These preliminary results may represent important clues for assessing the impact of the PRKAG3 gene on meat quality in cattle.