Structural characterisation of the acyl CoA: diacylglycerol acyltransferase 1 (DGAT1) gene and association studies with milk traits in Assaf sheep breed

• Low variability of DGAT1 gene was found in a panel of 9 breeds reared in Spain.
• A new DGAT1gene polymorphism was detected in exon 1 (g.358C > A).
• SNP g.8539 C > T has a significant effect on milk lactose content.
• SNP g.8539 C > T has a significant effect on C4:0, C16:1 c9, and the n-6:n-3 ratio.

Because DGAT1 plays a fundamental role in triacylglycerol synthesis, existing SNPs in DGAT1 gene might provide important information in partially explaining, the variation of milk fat content in dairy sheep. Therefore, the main objective of this study was to sequence the complete ovine acyl CoA:diacylglycerol acyltransferase 1 (DGAT1)gene in order to identify polymorphisms and to look for its possible association with milk traits in Assaf sheep breed. Polymorphisms identification in the DGAT1gene was carried out in 50 individuals belonging to five sheep breeds reared in Spain: Rasa Aragonesa (n = 10), Manchega (n = 10), Churra Tensina (n = 10), Latxa (n = 10) and Spanish Assaf (n = 10). The association studies between polymorphisms, and milk traits were carried out using animals belonging to three flocks of Assaf breed (n = 402). Four SNPs were detected, one in exon 1 (EU178818: g.358C > A), two in exon 17 (g.8522C > T and g.8539C > T), and one in intron 10 (g.7457C > A). The SNP in exon 1, g.358C > A,generates a non-conservative substitution at position p.Asp53Glu (GenBank ABW24130). The first SNP in exon 17 (g.8522C > T)causes an amino acid change at position p.Arg482Cys.The genotype frequencies were studied in a panel of 9 breed reared in Spain: Ansotana (n = 50), Latxa (n = 36), Romanov (n = 33), Rasa aragonesa (n = 55), Churra (n = 52), Churra tensina (n = 57), Churra lebrijana (n = 50), Manchega (n = 48) and Assaf (n = 402). All breeds were in Hardy–Weinberg equilibrium for all SNPs, except for the SNPs g.8522C > T and g.8539C > T SNPs which showed a deficit of heterozygous animals in Ansotana breed. This gene show low variability in a panel of 9 breeds reared in Spain. The only polymorphism not fixed in Assaf breed was the SNP g.8539C > T, and was used to test possible association with milk traits. The allelic frequency of the 8539C allele was 0.96, being 373 animals homozygous for the CC genotype and 29 heterozygous. The association studies showed that lactose, fatty acids C4:0, C16:1 c9, and the ratio n-6:n-3 were affected by the SNP g.8539C > T. Animals carrying the CC genotype had greater lactose, C4:0 and C16:1 c9 contents and lower ratio of n-6:n-3 compare to the CT ones. Probably the SNP g.8539C > T, is not causative of the variation observed in the lactose content but might be in linkage disequilibrium with the causal mutation located in the same or other closer gene.