The inefficiency of in vitro maturation (IVM) compared to in vivo maturation is due to spontaneous resumption of meiosis I in the oocyte when removed from the ovarian follicle. The cAMP is a key molecule that regulates oocyte maturation. A decrease in the oocyte cAMP leads to premature resumption of meiosis I and asynchrony between the nuclear and cytoplasmic maturation. Several substances that stimulate the synthesis or inhibiting degradation of cAMP in the oocyte have been used to simulate a physiological maturation and thus improving the in vitro embryos production (IVP). This knowledge led to the development of SPOM system (simulated physiological oocyte maturation), which consists of a prolonged period of maturation and simultaneously delayed nuclear maturation by the addition of substances that maintains the oocyte cAMP in high concentrations. The success of SPOM system in bovine and mice embryo production in vitro motivates further investigations regarding cellular and molecular mechanisms of this system. It is well known that the oocyte I, arrested at the germinal vesicle stage (GV), has high transcriptional activity. Consequently, blocking the maturation at this stage allows the storage of RNAs and proteins that will support the development of the embryo until its genome activation. Furthermore, the conventional maturation systems can modify the molecular mechanisms that regulate the oocyte development. Therefore, the present project aim to identify genes differentially expressed between the conventional IVM system and the SPOM. Cumulus-oocyte complexes, majority zebu obtained from an abattoir, will be matured (conventional and SPOM) and then analyzed regarding global gene expression by microarray technique. After microarray analysis, eight candidate genes will be selected by differential expression between the two systems and validated by real time PCR. The functionality of the SPOM system will be assessed by nuclear oocyte maturation and gap junction quantification in the cumulus cells. At the end of the IVP, blastocysts rates and embryo quality will also be assessed. We believe that the identification of genes differentially expressed, and the relation with their functions may help us to understand the mechanisms regulating oocyte maturation, and further to improve the conditions of IVM and bovine embryos production.
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