C-type natriuretic peptide pre-maturation culture affects cytoplasmic maturation in bovine oocytes†

In vitro oocyte maturation (IVM) is a vital step for many assisted reproductive technologies including in vitro embryo production. Modulation of ribonucleic acid (RNA) transcripts, lipids, mitochondria, and other molecules during maturation influences development significantly. To improve current maturation systems, inclusion of pre-maturation culture has been investigated to delay resumption of meiosis and allow appropriate progression of cytoplasmic maturation using C-type natriuretic peptide (CNP). In this study, the transcriptome and molecular fingerprint of germinal vesicle, conventional IVM, and CNP-IVM oocytes were compared to identify transcripts and associated pathways altered by CNP treatment. There were similar pathways associated with upregulated transcripts in both types of mature oocytes involved with mitochondrial function and translation. Oocytes that were matured under conventional conditions contained transcripts associated with messenger RNA surveillance, Polycomb repressive complex, and reactive oxygen species. Oocytes matured with CNP treatment contained transcripts associated with cofactor biosynthesis, autophagy, apoptosis, arginine and proline metabolism, and mechanistic target of rapamycin (mTOR). Compared to immature oocytes, all mitochondrial-derived protein encoding genes were upregulated after conventional IVM but not after CNP-IVM. The molecular fingerprint of lipid droplets was also significantly altered in CNP-treated oocytes. Overall, results of these experiments have demonstrated measurable transcriptomic and molecular differences in CNP treated oocytes that may enhance oocyte and embryo quality.