A Synonymous SNP in DGAT1 Affects Milk Fat Percentage of Dairy Sheep by Regulating the Stability of the mRNA to Change the Viability, Proliferation, and Triglyceride Levels of Ovine Mammary Epithelial Cells

Diacylglycerol O-acyltransferase1 (DGAT1) is a rate-limiting enzyme that catalyzes triglyceride synthesis originated from diacylglycerol and acyl-CoA. However, there have been no reports on the regulatory mechanism of single nucleotide polymorphisms (SNPs) of DGAT1 underlying lactation performance in sheep. In this study, three SNPs were detected in 476 dairy sheep by Penta-primer Amplification Refractory Mutation System (PARMS), including two SNPs (c.191 + 411 C > T and c.192-440 C > T) in the intron 1 and one SNP c.1461 C > T in exon 17 that was a synonymous mutation. The SNP c.191 + 411 C > T was related to average daily milk yield, while the ewes of the genotype CC at c.1461 had a higher milk fat percentage than those with the genotype CT. The SNP c.1461 C > T would lead to a change in the secondary structure of DGAT1 mRNA. It was further found that the wild genotype CC increased the stability of DGAT1 mRNA compared to that of the mutant genotype TT at c.1461. Moreover, the change of the stability regulated the activities of OMECs by affecting the expression of DGAT1. The genotype CC also remarkably increased the triglyceride levels of OMECs, and the expression levels of two milk fat synthesis genes fatty acid synthase (FASN) and proliferator-activated receptor gamma (PPARG). These results suggest that a synonymous SNP c.1461 C > T affects the milk fat percentage of dairy sheep by regulating the stability of DGAT1 mRNA to change the viability, proliferation and triglyceride levels of OMECs. These findings lay a theoretical foundation for using DGAT1 as a molecular marker to improve the lactation performance of dairy sheep.