Title: DNA polymorphisms and transcript abundance of PRKAG2 and AMPK in the rumen are associated with gain and feed intake in beef steers Authors
Submitted to: Animal Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 14, 2014
Publication Date: N/A
Interpretive Summary: Feed is the single largest input cost associated with beef production. Improving the efficiency that feed is converted to edible product would allow for improved biological and economic efficiency. Both feed intake and rate of body weight gain are heritable. Identifying genetic markers for these traits gives cattle breeders and feeders tools to select and manage cattle for feed efficiency. Previous research at the U.S. Meat Animal Research Center identified a large region on bovine chromosome four that was associated with feed intake and body weight gain. We have identified specific markers in that region that might be useful for selecting cattle for improved feed efficiency. Some of these markers for gain were found within the gene PRKAG2. Expression of this gene was confirmed in tissue from the intestine, muscle, and liver. The level of expression in rumen tissues is associated with feed intake. The PRKAG2 protein is a subunit of a larger protein, AMP-activated protein kinase, which is involved in cellular energy homeostasis and has roles in carbohydrate, lipid and protein metabolism, as well as cell growth and death. We evaluated the AMPK protein in the rumen and found that this protein was associated with feed intake. These data suggest that PRKAG2 and its mature heterotrimeric protein, AMPK are involved in feed efficiency traits in beef steers. This is the first evidence to suggest that the active AMPK protein in the rumen may be contributing to feed intake in cattle.
Technical Abstract: Beef steers with variation in feed efficiency phenotypes were evaluated previously on a high density SNP panel. Ten markers from rs110125325-rs41652818 on bovine chromosome 4 were associated with average daily gain (ADG). To identify the gene(s) in this 1.2Mb region responsible for variation in ADG, genotyping with 157 additional markers was performed. Several markers (n=41) were nominally associated with ADG and three of these, including the only marker to withstand Bonferroni correction, were located within the protein kinase, AMP-activated, gamma 2 non-catalytic subunit (PRKAG2) gene. An unrelated population of crossbred steers (n=406) was genotyped for validation. One marker located within the PRKAG2 loci approached significant association with gain. To evaluate PRKAG2 for differences in transcript abundance, we measured expression in the liver, muscle, rumen and intestine from steers (n=32) with extreme feed efficiency phenotypes collected over two seasons. No differences in PRKAG2 transcript abundance were detected in small intestine, liver, or muscle. Correlation between gene expression level of PRKAG2 in rumen and average daily feed intake (ADFI) was detected in both seasons (P<0.05); however, the direction differed by season. Lastly, we evaluated AMP-activated protein kinase (AMPK), of which PRKAG2 is a subunit, for differences among ADG and ADFI and found that the phosphorylated form of AMPK was associated with ADFI in the rumen. These data suggest that PRKAG2 and its mature protein, AMPK are involved in feed efficiency traits in beef steers. This is the first evidence to suggest that rumen AMPK may be contributing to ADFI in cattle.