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Mitochondrial glycerol-3-phosphate acyltransferase (GPAM) catalyses the initial and rate-regulated first-stage pathway of glycerol lipid synthesis and helps to allocate acyl-CoA (acyl-coenzyme A) to triglyceride (TG) synthesis and away from degradation pathways in animal lipometabolism-related pathways. In this study, RNA interference (RNAi) and GPAM gene overexpression were used to examine the correlation between the expression of GPAM and adipogenesis in bovine mammary epithelial cells (bMECs). Additionally, three novel polymorphisms were identified within the bovine key functional domain of GPAM with Sanger sequencing. The relationship between variants of the GPAM gene and milk quality traits of Chinese Holstein cows was then analysed using statistical methods. The results showed that knockdown of the GPAM gene significantly reduced the synthesis of triglycerides in the bMECs (p < 0.05), whereas the overexpression of the GPAM gene significantly increased the synthesis of TG (p < 0.05). In Chinese Holstein dairy cattle, the polymorphic locus of the GPAM gene E20-3386G > A was significantly correlated with fat, protein and somatic cell count (p < 0.05); I18-652A > G was significantly correlated with fat, total fat content, protein, dry matter and somatic cell count (p < 0.05); and I18-726A > G was significantly correlated with protein, milk yield, dry matter and somatic cell count (p < 0.05). Specifically, individuals with the AA genotype of the I18-652A > G and E20-3386G > A polymorphic loci had a higher milk fat percentage (p < 0.05). In summary, GPAM plays a pivotal role in the intracellular regulation of triglyceride, and its mutations could work as a competent molecular marker for selective breeding in dairy cattle.

In this study, we precisely constructed and transfected the overexpression and interference vectors in BFFs to evaluate the role of DLK1 gene on lipid metabolism in vitro. The expression of of DLK1 in the mRNA and protein level tended to reduce, and TGs were significantly increased in the pGPU6-shDLK1 group compared to the control group (p &lt, 0.05). The expression of DLK1 in the mRNA and protein level were increased in the pBI-CMV3-DLK1 group compared to the control group, and the TGs content showed a significant decrease in the pBI-CMV3-DLK1 group (p &lt, 0.05). Meanwhile, we used the restriction fragment length polymorphism (RFLP-PCR) detection method to screen SNPs further to explore and analyze the relationship between the gene and the economic traits of 28-month-old Chinese Simmental and the fatty acids composition of cattle longissimus muscle. The result showed that two SNPs, IVS3 + 478 C&gt, T and IVS3 + 609 T&gt, G, were identified as being significantly associated with carcass and meat quality traits in Chinese Simmental, such as the carcass fat coverage rate, loin eye muscle area, and fat color score. In summary, our results indicated that DLK1 can affect lipid metabolism in bovine and these two SNPs might be applied as genetic markers of meat quality traits for beef cattle breeding.