- Type :
- Soutenance de thèse
- Lieu :
- D7-2016 - Faculté des sciences
M. Achu Ammah Adolf
Pr François Malouin, Département de biologie, Université de Sherbrooke
Membres du jury :
Pre Eveline Ibeagha-Awemu, directrice de recherche, Agriculture et Agroalimentaire Canada
Pr Nicolas Gévry, codirecteur de recherche, Département de biologie, Faculté des sciences, Université de Sherbrooke
Pre Rachel Gervais, évaluatrice externe, Département des sciences animales, Faculté des sciences de l’agriculture et de l’alimentation, Université de Laval
Pre Nathalie Bissonnette, évaluatrice interne, Agriculture et Agroalimentaire Canada
The molecular mechanisms and biological processes that occur in the cell following dietary supplementation with unsaturated fatty acids (USFA), resulting in the expression of genes or sets of genes that are co-expressed and eventually direct the expression of phenotypes (blood and milk metabolites) are not fully understood. Considering the importance of USFA to man, different techniques (dietary and genetics) have been used to increase the proportion of beneficial FA in milk. Dietary supplementation with LSO and SFO has been used but it is not clear what residual effects these nutrients have on the physiology of the animal including blood metabolites and milk components or for how long effects are active after withdrawal from the diet. In the first part of my Ph.D. study (Chapter 1), I presented general background information on bovine milk and blood components, classification and importance of FA and mammary gland transcriptome profiling etc. In the second part, I examined the treatment and post treatment effects of dietary supplementation of cows’ diets with 5% LSO or 5% SFO on milk composition and blood metabolites of lactating Holstein cows.
Thirdly, I determined the relationship between the blood and milk metabolites and high interacting microRNA (miRNA) modules, and mRNA/miRNA co-expression data from the mammary gland of the same animals. The mRNA transcriptome analysis identified 1,006 (460 up and 546 down-regulated) and 199 (127 up and 72 down-regulated) genes that were significantly differentially regulated by LSO and SFO, respectively, meanwhile the miRNA transcriptome analysis detected 14 and 22 miRNAs that were significantly differentially regulated by LSO and SFO, respectively. However, since a network of genes and regulatory factors work in concert to influence the phenotypic expression of traits, assessment of gene expression without considering the factors that regulate their activities may not adequately explain the complex biological mechanisms underlying the expression of traits. Moreover, miRNAs interact with mRNA(s) to regulate their expression and consequently biological processes, so it is important to study their synergistic effects on the phenotypic expression of traits (blood and milk components). For these reasons, I determined the relationship between the traits (milk and blood parameters) and miRNA modules and miRNA-mRNA pairs following dietary supplementation with 5%LSO or 5% SFO. As the third part of my PhD studies, I investigated the co-expression patterns of high interacting miRNAs and miRNA-mRNA pairs and the key regulatory network of genes that influence blood and milk phenotypes following dietary supplementation with USFA.
Dietary modifications through feeding trials is an effective way to rapidly modify milk fat composition. However, the effects of dietary supplementation are totally revocable when feeding conditions change, coupled with low conversion efficiency of dietary FA into milk USFA due to ruminal biohydrogenation of dietary FA in the rumen of the animal. Furthermore, candidate gene studies have demonstrated that SNP in some key lipogenic genes like diacylglycerol o-acyltransferase 1 (DGAT1), sterol regulatory element binding protein-1 (SREBP1) and stearoyl-CoA desaturase (SCD) influence milk fat composition, which also explains part of the genetic variation of milk fat unsaturation indices seen in Holsteins and Brown Swiss cows. Therefore, I investigated the associations between SNPs on genes that were differentially expressed as a result of dietary supplementation with USFA with de novo synthesized fatty acid profiles of Canadian Holstein cows as the fourth part of my Ph.D. studies. To achieve this, SNPs in genes that were differentially expressed as a result of dietary supplementation with USFA. were studied for their association with milk de novo synthesized FA in Holstein milk from 18 herds in Quebec.
In conclusion, this study provides insights on the molecular mechanisms that occur in the bovine mammary gland following dietary supplementation with 5% LSO and 5% SFO.