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Effect of C-type natriuretic peptide on maturation and developmental competence of immature mouse oocytes in vitro.

In vitro maturation (IVM) of oocytes is an important assisted reproductive technology for infertility treatment and livestock breeding programs. Because of asynchronous nuclear and cytoplasmic maturation, the developmental competence of oocytes matured in vitro is compromised. C-Type natriuretic peptide (CNP), which has been proved to be an inhibitor of oocyte maturation, provides a new alternative to optimise synchronisation of nuclear and cytoplasmic maturation and improve developmental capacity of immature oocytes in vitro. To investigate the effect of temporary meiotic arrest mediated by CNP on maturation and subsequent development of immature oocytes, immature mouse oocytes from small antral follicles were temporarily arrested in meiosis by CNP (0, 5, 10 and 50nM) for 24h and then matured for 16h. CNP treatment significantly increased the oocyte maturation rate from less than half to above 80%. After IVF, temporary meiotic arrest mediated by 10 and 50nM CNP significantly improved fertilisation and blastocyst rate of oocytes matured in vitro up to approximately 55% and 30% respectively. Moreover, this positive effect of CNP was attributed, in part, to an increase in the number of mature oocytes with aligned chromosomes and a normal spindle. The present findings indicate the potential to use CNP to improve the efficiency of oocyte IVM.