# METTL14 Promotes Lipid Synthesis in Dairy Goat Mammary Epithelial Cells by Targeting CEBPB via m6A-YTHDF1/3-Dependent Manner

## TL;DR

This study shows that METTL14 boosts milk fat production in dairy goats by modifying CEBPB through m6A RNA methylation, offering new ways to improve dairy farming.

## Contribution

The study reveals a novel m6A-dependent mechanism by which METTL14 regulates milk fat synthesis in dairy goats via CEBPB.

## Key findings

- METTL14 overexpression increases triglyceride and cholesterol synthesis in goat mammary cells.
- METTL14 induces m6A modification at site 1662 of CEBPB mRNA, enhancing its translation via YTHDF1/3.
- Reducing METTL14 suppresses lipid biosynthesis and droplet accumulation in mammary epithelial cells.

## Abstract

As one of the key methyltransferases of m6A, METTL14 exhibited a regulatory role in fat metabolism in previous studies. However, direct functional validation of its role in milk fat metabolism of dairy goats is currently lacking. Our study elucidates how METTL14, a core “Writer” of m6A RNA methylation modification, regulates milk fat synthesis in dairy goats. By adjusting METTL14 level in goat mammary epithelial cells, we demonstrated that METTL14 overexpression boosts triglyceride and cholesterol biosynthesis and lipid droplet accumulation, while reducing METTL14 suppresses these metabolic processes. Mechanistically, METTL14 mediates m6A modification at a specific site of CEBPB transcripts, which is subsequently recognized by m6A “Readers” YTHDF1/3, leading to the activation of lipogenic programs. These findings establish an epigenetic paradigm for m6A-mediated regulation of milk fat synthesis and propose novel strategies for optimizing dairy production through molecular breeding.

N6-methyladenosine (m6A), a predominant and reversible modification of mammalian RNA, plays a critical role in regulating growth, development, and metabolism. While methyltransferase-like 14 (METTL14) is an essential component of the m6A methyltransferase complex, its specific function in regulating milk fat metabolism in dairy goats remains unexplored. This study therefore aimed to elucidate the role of METTL14 in lipid metabolism within dairy goat mammary epithelial cells (GMECs). METTL14 overexpression significantly promoted the synthesis of TAG (Triacylglycerol) and TC (Total cholesterol), as well as lipid droplet accumulation in GMECs. Furthermore, METTL14 upregulated CCAAT enhancer binding protein beta (CEBPB) expression at both the mRNA and protein levels by directly inducing m6A modification on its transcripts. Finally, we confirmed that m6A modification occurs specifically at site 1662 of CEBPB mRNA, and the “Readers” YTH N6-methyladenosine RNA binding protein F1 and F3 (YTHDF1/3) were found responsible for the m6A site recognition and interpretation. This study demonstrated that METTL14 facilitates lipid synthesis and deposition in GMECs. Mechanistically, METTL14 installs the m6A modification at site 1662 of CEBPB transcripts. This m6A mark is specifically recognized by the readers YTHDF1 and YTHDF3, which promote the translation of CEBPB mRNA, thereby upregulating its expression.