Oocyte maturation plays a vitally important role in the reproduction of pigs. However, the roles of messenger RNAs (mRNAs) and long non‐coding RNAs (lncRNAs) in the developmental process of porcine oocyte maturation are still largely unclear. In this study, a transcriptome analysis of germinal vesicle (GV) and metaphase II (MII) of oocytes from Chinese Duroc pigs was performed. A total of 1,753,030 and 2,486 differentially expressed (DE) mRNAs, 22,811 and 9,868 DE lncRNAs were identified between GV and MII stages, respectively. Furthermore, functional enrichment analysis showed that the common DE mRNAs and DE lncRNAs during the process of maturation were mainly involved in biological process and cellular components. Our study provides new insights of the expression changes of mRNAs and lncRNAs during GV and MII stages, which might contribute to the maturation of oocytes. These results greatly improve our understanding of the molecular mechanisms regulating the maturation of oocytes in pigs.

The quality of oocytes is closely associated with the successful production of porcine oocytes in vitro. However, the regulating mechanisms of oocytes in vitro maturation (IVM) need to be further improved, and the quality of oocyte maturation in vitro is still inferior to that of oocyte maturation in vivo. Compared with oocytes matured in vivo, the oocytes matured in vitro tend to have such problems as more high precision fertilization rate, low blastocyst formation rate, not fully unified oocyte cytoplasm and nuclei of mature in the current maturation systems (Jiao et al., 2020). Moreover, the mature quality of porcine oocytes has an essential effect on embryo development after in vitro fertilization (IVF), nuclear transfer (NT) and parthenogenetic activation (PA) (Kim et al., 2010). Oocyte

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Quercetin (QUE) is a component of the flavonoid family that shows various therapeutic properties, such as antioxidant effects. However, whether QUE affects porcine oocyte in vitro aging has not yet been investigated. Therefore, in this study, we applied various doses of QUE to freshly isolated porcine oocytes and found that 10 µM QUE improved the oocyte maturation rate in vitro, as reflected by the increased degree of cumulus cell expansion and first polar body extrusion. More importantly, we found that QUE reduced in vitro aging and improved the maturity level of porcine oocytes after another 24 h of culturing, accompanied by the upregulated expression levels of bone morphogenetic protein 15, growth differentiation factor 9, Moloney sarcoma oncogene, and cyclin-dependent kinase 2. In addition, we found that QUE treatment significantly reduced the intracellular reactive oxygen species levels, apoptosis, and autophagy and upregulated the expression levels of superoxide dismutase 2 and catalase in aged porcine oocytes. In addition, QUE restored impaired mitochondrial membrane potential and spindle assembly in aged porcine oocytes. Our findings demonstrate that QUE can protect porcine oocytes from in vitro aging by reducing oxidative stress and maintaining mitochondrial function.