title: Deep sequencing shows microRNA involvement in bovine mammary gland adaptation to diets supplemented with linseed oil or safflower oil.
abstract: BACKGROUND
  Bovine milk fat composition is responsive to dietary manipulation providing an avenue to modify the content of fatty acids and especially some specific unsaturated fatty acid (USFA) isomers of benefit to human health. MicroRNAs (miRNAs) regulate gene expression but their specific roles in bovine mammary gland lipogenesis are unclear. The objective of this study was to determine the expression pattern of miRNAs following mammary gland adaptation to dietary supplementation with 5 % linseed or safflower oil using next generation RNA-sequencing.
  
  
  METHODS
  Twenty-four Canadian Holstein dairy cows (twelve per treatment) in mid lactation were fed a control diet (total mixed ration of corn:grass silages) for 28 days followed by a treatment period (control diet supplemented with 5 % linseed or safflower oil) of 28 days. Milk samples were collected weekly for fat and individual fatty acid determination. RNA from mammary gland biopsies harvested on day-14 (control period) and on days +7 and +28 (treatment period) from six randomly selected cows per treatment was subjected to small RNA sequencing.
  
  
  RESULTS
  Milk fat percentage decreased significantly (P < 0.001) during treatment with the two diets as compared to the control period. The individual saturated fatty acids C4:0, C6:0, C8:0, C14:0 and C16:0 decreased significantly (P < 0.05) while five USFAs (C14:1, C18:1n11t, C20:3n3, C20:5n3 and CLA:t10c12) increased remarkably (P < 0.05) in response to both treatments. Analysis of 361 million sequence reads generated 321 known bovine miRNAs and 176 novel miRNAs. The expression of fourteen and twenty-two miRNAs was affected (P < 0.05) by linseed and safflower oil treatments, respectively. Seven miRNAs including six up-regulated (bta-miR-199c, miR-199a-3p, miR-98, miR-378, miR-148b and miR-21-5p) and one down-regulated (bta-miR-200a) were found to be regulated (P < 0.05) by both treatments, and thus considered core differentially expressed (DE) miRNAs. The gene targets of core DE miRNAs have functions related to gene expression and general cellular metabolism (P < 0.05) and are enriched in four pathways of lipid metabolism (3-phosphoinositide biosynthesis, 3-phosphoinositide degradation, D-myo-inisitol-5-phosphate metabolism and the superpathway of inositol phosphate compounds).
  
  
  CONCLUSIONS
  Our results suggest that DE miRNAs in this study might be important regulators of bovine mammary lipogenesis and metabolism. The novel miRNAs identified in this study will further enrich the bovine miRNome repertoire and contribute to understanding mammary gland biology.
authors.affiliation: Agriculture and Agri-Food Canada, Dairy and Swine Research and Development Centre, Sherbrooke, Quebec, J1M 0C8, Canada.|College of Animal Science and Technology, Northwest A&F University, Xi'an, Shaanxi, 712100, China.
authors.forename: Ran
authors.initials: R
authors.lastname: Li
authors.affiliation: Agriculture and Agri-Food Canada, Dairy and Swine Research and Development Centre, Sherbrooke, Quebec, J1M 0C8, Canada.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Beaudoin
authors.affiliation: Agriculture and Agri-Food Canada, Dairy and Swine Research and Development Centre, Sherbrooke, Quebec, J1M 0C8, Canada.
authors.forename: Adolf A
authors.initials: AA
authors.lastname: Ammah
authors.affiliation: Agriculture and Agri-Food Canada, Dairy and Swine Research and Development Centre, Sherbrooke, Quebec, J1M 0C8, Canada.
authors.forename: Nathalie
authors.initials: N
authors.lastname: Bissonnette
authors.affiliation: Agriculture and Agri-Food Canada, Dairy and Swine Research and Development Centre, Sherbrooke, Quebec, J1M 0C8, Canada.
authors.forename: Chaouki
authors.initials: C
authors.lastname: Benchaar
authors.affiliation: Department of Animal Science, McGill University, Ste-Anne-de-Bellevue, Quebec, H9X 3V9, Canada.
authors.forename: Xin
authors.initials: X
authors.lastname: Zhao
authors.affiliation: College of Animal Science and Technology, Northwest A&F University, Xi'an, Shaanxi, 712100, China.
authors.forename: Chuzhao
authors.initials: C
authors.lastname: Lei
authors.affiliation: Agriculture and Agri-Food Canada, Dairy and Swine Research and Development Centre, Sherbrooke, Quebec, J1M 0C8, Canada. eveline.ibeagha-awemu@agr.gc.ca.
authors.forename: Eveline M
authors.initials: EM
authors.lastname: Ibeagha-Awemu
mesh_terms: D000220:Adaptation, Biological / Q000235:genetics*; D000818:Animals; D002417:Cattle; D019587:Dietary Supplements; D005227:Fatty Acids / Q000378:metabolism; D005260:Female; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D015723:Gene Library; D059014:High-Throughput Nucleotide Sequencing; D006801:Humans; D008043:Linseed Oil; D008321:Mammary Glands, Animal / Q000378:metabolism*; D035683:MicroRNAs / Q000235:genetics*; D008892:Milk / Q000378:metabolism; D015203:Reproducibility of Results; D012450:Safflower Oil; D059467:Transcriptome
chemical_list: D005227:Fatty Acids; D035683:MicroRNAs; D012450:Safflower Oil; D008043:Linseed Oil