Previous studies have shown that BMI-1026 is a potent inhibitor of the cyclin-dependent kinases (cdk). In cell culture, the compound also arrests G2/M strongly and G1/S and S weakly. Two key kinases, cdk1 (p34cdc2 kinase) and mitogen-activated protein (MAP) kinase (erk1 and 2), perform crucial roles during oocyte maturation and, later, metaphase II (MII) arrest. In mammalian oocytes, both kinases are activated gradually around the time of germinal vesicle breakdown (GVBD) and maintain high activity in eggs arrested at metaphase II. In this study, we examined the effects of BMI-1026 on GVBD and MII arrest in mouse oocytes. BMI-1026 inhibited GVBD of immature oocytes and activated MII-arrested oocytes in a concentration-dependent manner, with more than 90% of oocytes exhibiting GVBD inhibition and MII activation at 100 nM. This is approximately 500～1,000 times more potent than the activity reported for the cdk inhibitors roscovitine (~50 M) and butyrolactone (～100 M). Based on the results of previous in vitro kinase assays, we expected BMI-1026 to inhibit only cdk1 activation in oocytes and eggs, not MAP kinase. However, in our cell-based system, it inhibited the activity of both kinases. We also found that the effect of BMI-1026 is reversible. Our results suggest that BMI-1026 inhibits GVBD and activates MII-arrested oocytes efficiently and reversibly and that it also inhibits both cdk1/histone H1 kinase and MAP kinase in mouse oocytes.

ABSTRACT   INTRIDUSTION   MATERIALS AND METHODS    Collection of Oocytes and Eggs    Culture of Oocytes and Eggs    Histone H1 and MBP Double-Kinase Assay    Evaluation of GVBD, Egg Activation and 2nd Polar Body Extrusion    Statistical Analysis   RESULTS    Effect of BMI-1026 on GVBD of Immature Oocytes    Effect of BMI-1026 on Histone H1 and MAP Kinases Activation    Effect of BMI-1026 on Activation of Ovulated Eggs    Reversibility of BMI-1026 on GVBD Inhibition   DISCUSSION   REFERENCES

• Tae-Saeng Choi(Department of Microbiology, College of Medicine, Dankook Uinversity)