MSI2 expression in single vs. double dominant follicles and its role in Mongolian sheep fecundity

Musashi 2 (MSI2), a conserved RNA-binding protein, is important in mammalian sperm and follicle development. Its function in Mongolian sheep, however, remains unclear. We investigated the differential expression of MSI2 in single and double dominant follicles of Mongolian sheep and its role in prolificacy. Sixty 7-month-old Mongolian ewes in estrus were studied. The results showed that MSI2 was expressed in Mongolian sheep ovarian granulosa cells, and the mRNA and protein expression levels of MSI2 were significantly higher in single dominant follicles than in double dominant follicles. There were 3400 DEGs in the single and double dominant follicles of Mongolian sheep, which were mainly enriched in steroidogenesis, TGF-β, and estrogen signaling pathways; based on PPI analysis, further studies were conducted on CYP17A1, ERβ, StAR, and 3β-HSD that interact with MSI2. It has been confirmed that they are coexpressed in Mongolian sheep ovarian granulosa cells. The mRNA and protein expression levels of MSI2 and CYP17A1 in double dominant follicles were significantly lower than those in single dominant follicles, with a significant positive correlation. In contrast, 3β-HSD, StAR, and ERβ were more highly expressed in double follicles, correlating negatively with MSI2. It is speculated that reduced expression of MSI2 and CYP17A1 in double dominant follicles promotes the expression of StAR, 3β-HSD, and ERβ, thereby facilitating the formation of double dominant follicles in Mongolian sheep. This study confirms that MSI2 may serve as an essential regulatory factor for Mongolian sheep multiparity trait, providing a theoretical basis for further research on the trait.