miR-143 is critical for the formation of primordial follicles in mice.

Although microRNAs (miRNAs) have been implicated in fine-tuning gene networks, the roles of mmu-mir-143 (miR-143) in mammalian ovary development have not been studied in vitro. We investigated the expression and function of miR-143 in the mouse ovary during primordial follicle formation. Real-time polymerase chain reaction analysis showed that miR-143 expression increased during primordial follicle formation from 15.5 days post-coitus to 4 days post-partum. miR-143 was located in pregranulosa cells by in situ hybridization. To study the function of miR-143 in primordial follicle formation we established an electroporation transfection model in vitro that allowed miR-143 expression to be efficiently upregulated and inhibited in cultured ovaries. Further studies showed that miR-143 inhibited the formation of primordial follicles by suppressing pregranulosa cell proliferation and downregulating the expression of genes related to the cell cycle. These findings suggest that miR-143 is critical for the formation of primordial follicles and regulates ovarian development and function.