MicroRNA-342-3p regulates yak oocyte meiotic maturation by targeting DNA methyltransferase 1

MicroRNAs (miRNAs) play vital roles in the development of oocytes and ovarian follicles. We have previously shown differential expression of miR-342-3p during yak oocyte maturation. In this study, we investigated the role of miR-342-3p in meiotic maturation of yak oocytes and the underlying mechanism. The profile of ovarian DNA methyltransferase 1 (DNMT1) expression was investigated in yak by RT-qPCR and western blot analyses. The pattern of Dnmt1 expression in various meiotic stages (GV stage, MI stage and MII stage) of yak oocyte maturation was then measured by immunofluorescence staining. The interaction between Dnmt1 and miR-342-3p was verified by dual-luciferase reporter assay. Finally, miR-342-3p inhibitors were microinjected into yak cumulus-oocyte complex to evaluate the effects on oocyte maturation. MiR-342-3p expression was upregulated in oocytes during meiotic maturation, with significantly higher levels in the MII stage compared with the GV- and MI stages (p < .05), whereas the opposite pattern of Dnmt1 expression was detected. In the period to sexual maturity (3-year-old), DNMT1 showed an age-related pattern of ovarian expression at both the gene and protein levels. Immunohistochemistry analysis also indicated maturation-stage-related differences in DNMT1 expression in the ovarian follicles and corpus luteum, with expression predominantly detected in cumulus cells and oocytes. MiR-342-3p inhibitors effectively upregulated Dnmt1 expression and significantly inhibited oocyte meiotic maturation. Taken together, our results indicate that miR-342-3p plays a vital role in the meiotic maturation of yak oocytes by targeting the 3'-untranslated regions (UTR) of Dnmt1 and provide a new perspective on the mechanism of this process.