Meimei Zhang

Fatty acid composition is a key factor affecting the flavor and quality of goat milk. CircRNAs are now recognized as important regulators of transcription, and they play an important role in the control of fatty acid synthesis. Thus, understanding the regulatory mechanisms controlling this process in ruminant mammary glands is of great significance. In the present study, mammary tissue from dairy goats during early lactation and the dry period (nonlactating) were collected and used for high-throughput sequencing. Compared to levels during the dry period, the expression level of circ003429 during early lactation was lower (12.68-fold downregulated). In isolated goat mammary epithelial cells, circ003429 inhibited the synthesis of triglycerides (TAG) and decreased the content of unsaturated fatty acids (C16:1, C18:1, and C18:2), indicating that this circRNA plays an important role in regulating lipid synthesis. A binding site for miR-199a-3p in the circ003429 sequence was detected, and a dual-luciferase reporter system revealed that circ003429 targets miR-199a-3p. Overexpression of circ003429 (pcDNA-circ003429) downregulated the abundance of miR-199a-3p. In contrast, overexpression of miR-199a-3p increased TAG content and decreased mRNA abundance of Yes-associated protein 1 (YAP1) (a target gene of miR-199a-3p), and TAG content was decreased and mRNA abundance was increased in response to overexpression of circ003429. These results indicate that circ003429 alleviates the inhibitory effect of miR-199a-3p on the mRNA abundance of YAP1 by binding miR-199a-3p, resulting in subsequent regulation of the synthesis of TAG and unsaturated fatty acids.

The aim of the study was to understand the internal relationship between milk quality and lipid metabolism in cow mammary glands. A serial of studies was conducted to assess the molecular mechanism of PRL/microRNA-183/IRS1 (Insulin receptor substrate) pathway, which regulates milk fat metabolism in dairy cows. microRNA-183 (miR-183) was overexpressed and inhibited in cow mammary epithelial cells (CMECs), and its function was detected. The function of miR-183 in inhibiting milk fat metabolism was clarified by triglycerides (TAG), cholesterol and marker genes. There is a CpG island in the 5′-flanking promoter area of miR-183, which may inhibit the expression of miR-183 after methylation. Our results showed that prolactin (PRL) inhibited the expression of miR-183 by methylating the 5′ terminal CpG island of miR-183. The upstream regulation of PRL on miR-183 was demonstrated, and construction of the lipid metabolism regulation network of microRNA-183 and target gene IRS1 was performed. These results reveal the molecular mechanism of PRL/miR-183/IRS1 pathway regulating milk fat metabolism in dairy cows, thus providing an experimental basis for the improvement of milk quality.