miR-to-miR interactions: Investigating the effects of miR-21 down-regulation and bisphenol exposure in COCs, arrested 8-cell embryos and blastocysts.

Endocrine disrupting compounds (EDCs) including bisphenol A (BPA), bisphenol S (BPS) and bisphenol F (BPF) have the potential to alter microRNAs (miRs) expression and elicit negative effects on reproduction. miR-21 is one of the most dynamic miRs, abundantly expressed in oocytes and embryos, and is affected by BPA exposure. miR-21 dysregulation and bisphenol exposure might influence key miRs (miR-10b, -29a, -34c, -103a, -130, -146, -155, -224, -378, and -499) important for oocyte maturation, embryonic genome activation (EGA) and early embryonic development. We aimed to test the hypothesis that expression of key miRs during oocyte maturation and in vitro embryo production is affected by anti-miR-21 and bisphenols in a miR-21-dependent manner, shedding light on the concept of miR-to-miR interaction. miR-21 may positively co-regulate apoptotic pathways with miR-103a, miR-155 and miR-29a, and inversely with miR-34c, and participate in a shared pathway for progesterone signalling with miR-155. These processes may have implications in regulating each other's biogenesis or feedback loops. Proper oocyte maturation is vital for oocyte competence and resulting embryo development; thus, reduced maturation rates (p < 1 ×10-11) resulted in lower cleavage (p = 0.001) and blastocyst rates (p = 0.0022) in anti-miR-21 and BPA, BPS, and BPF groups. Additionally, apoptosis, detected in blastocysts using TUNEL staining, showed that BPA, BPS and BPF treatment increased DNA fragmentation (p < 0.05). Overall, this study deepens our understanding of miR-to-miR interactions and the effect of EDCs on epigenetic modulation affecting oocyte competence and in vitro early embryonic development, ultimately aimed at improving Artificial Reproductive Technologies in humans and animals.