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Mitochondrial genome diversity and association of mitochondrial protein gene expression with energy metabolism in dairy cattle.

J. Dorji

Abstract:

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Mitochondrial genome diversity and association of mitochondrial protein gene expression with energy metabolism in dairy cattle.
J. Dorji*1,2, C. J. Vander Jagt2, J. B. Garner3, L. C. Marett2, B. A. Mason2, C. M. Reich2, C. P. Prowse-Wilkins2,4, R. Xiang2,4, P. N. Ho2, J. Pryce1,2, B. G. Cocks1,2, A. J. Chamberlain2, I. M. MacLeod2, H. D. Daetwyler1,2. 1School of Applied Systems Biology, La Trobe University Bundoora, Victoria, Australia, 2Agriculture Victoria, AgriBio, Centre for AgriBioscience Bundoora, Victoria, Australia, 3Agriculture Victoria, Ellinbank Dairy Centre Ellinbank, Victoria, Australia, 4Faculty of Veterinary & Agricultural Science, University of Melbourne Parkville, Australia.

Mitochondria are primarily organelles for cellular energy metabolism and have a maternally inherited genome encoding 37 genes. Proteins from these genes interact with mitochondrial proteins (MP) encoded by nuclear genes to enable mitochondrial functions. Given the key role of mitochondria in energy production, mutations affecting the expression of MP genes could have flow-on effects on important traits in cattle. Our study had 3 aims: first to assess the diversity of the mitochondrial genome of modern dairy cattle breeds, second, to characterize MP gene expression across tissues within animals, and third, to correlate MP gene expression in blood with feed efficiency in dairy cattle. Mitochondrial genome diversities (nucleotide and haplotype) were estimated based on selected variant positions across the genome. Overall, there was a low diversity in the dairy breeds studied. Broadly, the modern dairy cattle (e.g., Holsteins) were predominantly T3 (~95%, with > 10 evident subgroups) and to a lesser extent T2 and T1 haplogroups. Gene expression in tissue as was quantified by RNA sequencing. We used differential expression and co-expression analyses of genes in 29 tissues from 2 cows. We found consistent overexpression in high energy demand tissues (e.g., heart). This suggests that MP gene expression might also differ between animals that differ within tissue energy demands. We, therefore, measured gene expression in blood samples of 2 groups (14 dairy cows each) divergent for feed efficiency to analyze the differential gene expression and co-expression networks. There were 395 genes differentially expressed (DE) between high and low feed efficiency groups, of which 55 were MP genes. Furthermore, DE genes were significantly enriched for oxidative phosphorylation (OxPhos), an important pathway that generates cellular energy. However, none of the DE MP genes was from the mitochondrial genome. The association between feed efficiency and expression of MP genes involved in the OxPhos pathway was also evident in a weighted gene co-expression network analysis (r = 0.47, P = 0.01). Altogether, our study suggests that there is low mitochondrial genomic diversity among popular dairy breeds and MP gene expression may be associated with variation in traits linked to mitochondrial function.

Keywords: mitogenome, gene expression, cattle.

Biography: Jigme Dorji is a PhD candidate at AgriBio, Centre for AgriBioscience and School of Applied Systems Biology, La Trobe University, Bundoora, Australia. Jigme investigates the role of mitochondrial DNA in prediction dairy traits and understanding cow families employing mitochondrial genomic tools. Jigme headed Animal Genetic Resources Program and was the National Coordinator for Animal Genetic Resource working on farm animal genetic diversity assessment, conservation and management at the National Biodiversity Centre and served as a Research Officer at National Livestock Research Program under the Ministry of Agriculture and Forests, Bhutan from 2007 to 2017.