Improved in vitro methods are required to synchronize meiotic resumption and to allow all collected oocytes to complete nuclear maturation without affecting oocyte quality in order to maximize embryo production. The use of physiological or pharmacological inhibitors can thus be envisaged. Roscovitine (ROS), as a selective cdc2 inhibitor, has been reported to inhibit MPF and MAP kinase activity and maintains the oocyte at Germinal Vesicle (GV) stage. The aim of the present study was to investigate the effects of ROS on nuclear maturation of sheep oocytes. So, different concentrations of ROS (6.25, 12.5 and 25 lM) added to maturation medium. After 26 h exposition to ROS, the results indicated that the percentage of oocytes at GV stage was 2.41, 2.29 and 8.39% for 6.25, 12.5 and 25 lM Roscovitine concentration, respectively. Also, percentage of oocytes at MII stage was significantly (p,0.05) higher in control group oocytes (75.3%) than in oocytes exposed to 12.5 and 25 lM ROS (30.77 and 7.5 respectively). To evaluate if this effect was reversible and if a retardation or inhibition had occurred in the progression from GV to MII, oocytes were cultured in presence of the same concentrations of ROS for 26 h followed by culture for an additional 24 h in medium without ROS. After 50 h, the results showed that the oocytes can promote to MII. According to these results, roscovitine can postpone meiosis of sheep oocyte and it may improve cytoplasmic maturation and subsequently embryo production.

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