Gamete Biology

Effect of Phosphodiesterase Type 3 Inhibitor on Developmental Competence of Immature Mouse Oocytes In Vitro

Abstract
In vitro use of arresters of meiosis could improve cytoplasmic maturation of immature oocytes by controlling the period of prophase I. Phosphodiesterases (PDE) are responsible for the breakdown and concomitant inactivation of the cyclic nucleotides cAMP and cGMP and are implicated in the regulation of oocyte meiotic maturation. Selective inhibitors of phosphodiesterase type 3 (PDE3) prevent meiotic resumption of mammalian oocytes. This study evaluated the impact of meiosis arrest by PDE3 inhibitor, Org 9935, on developmental competence of GV-stage oocytes from small antral follicles. Cumulus-oocyte complexes (COC), retrieved from antral follicles 24 h after PMSG exposure and cultured in the presence of PDE3 inhibitor (10 µM) for an additional 24 h, remained arrested in the meiotic prophase. The GV configuration of oocytes before and after the arrest by PDE3 inhibitor was examined. After the period of meiosis arrest, a significantly increased proportion of oocytes had acquired a nucleolus surrounded by a condensed chromatin rim at the GV, which is a morphological correlate of transcriptional repression. Removal of inhibitor resulted in 90.6% ± 8.3 of oocytes with the first polar body extruded. Fertilization was significantly improved in oocytes that had been arrested compared to oocytes collected 24 h after PMSG and undergoing in vitro maturation immediately. Embryonic pre-implantation and live offspring rates of arrested oocytes were higher, although not significantly, than those of non-arrested oocytes. These results suggest that a temporal block of meiosis by PDE3 inhibitor promotes developmental competence of mice oocytes retrieved from small antral follicles.

Key words: Embryo • Fertilization • Meiosis • Oocyte development • Phosphodiestrases

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