EEF1D facilitates milk lipid synthesis by regulation of PI3K-Akt signaling in mammals.

Mammal's milk is an abundantly foremost source of proteins, lipids, and micronutrients for human nutrition and health. Understanding the molecular mechanisms underlying synthesis of milk components provides practical benefits to improve the milk quality via systematic breeding program in mammals. Through RNAi with EEF1D in primary bovine mammary epithelial cells, we phenotypically observed aberrant formation of cytoplasmic lipid droplets and significantly decreased milk triglyceride level by 37.7%, and exploited the mechanisms by which EEF1D regulated milk lipid synthesis via insulin (PI3K-Akt), AMPK, and PPAR pathways. In the EEF1D CRISPR/Cas9 knockout mice, incompletely developed mammary glands at 9th day postpartum with small or unformed lumens, and significantly decreased triglyceride concentration in milk by 23.4% were observed, as well as the same gene expression alterations in the three pathways. For dairy cattle, we identified a critical regulatory mutation modifying EEF1D transcription activity, which interpreted 7% of the genetic variances of milk lipid yield and percentage. Our findings highlight the significance of EEF1D in mammary gland development and milk lipid synthesis in mammals.