Butyrolactone I reversibly alters nuclear configuration, periooplasmic microtubules and development of porcine oocytes

Abstract

In the present study, we investigated the effects of specific cdc2 kinase inhibitor, butyrolactone I (BL I) on the prevention of germinal vesicle breakdown, changes of microtubular structures, and development of porcine oocytes after removal of the drug. In Experiment 1, cumulus–oocyte complexes (COCs) were cultured (44 h) in NCSU-23 medium containing different concentrations of BL I. The percentages of oocytes remaining at GV stage were 0, 0, 32, 80, and 84% ( P < 0.05), and the maturation rates were 86, 63, 30, 0, and 0% ( P < 0.05) for oocytes treated with 0, 10, 20, 40, and 80 μM of BL I, respectively. When oocytes were released from BL I incubation (Experiment 2) and cultured for an additional 44 h, 79, 84, and 83% of oocytes resumed meiosis, but only 52, 38 and 17% of oocytes reached normal metaphase II (MII) stage in the groups treated with 20, 40 and 80 μM BL I, respectively. In Experiments 3–5, reversibility and development of oocytes and embryos were evaluated after removal of the inhibitor. A reduced duration of BL I incubation (22 h) at 20 μM increased the percentage of oocytes remaining at the GV stage compared to the control group (85% versus 9%, P < 0.05). Blastocyst rates were lower in treatment groups than in the control (44 h) group (0–14% versus 24%; P < 0.05). However, all developing blastocysts possessed similar cell numbers, regardless of the drug-treated or non-treated controls. Taken together, treatment with 20–80 μM of BL I effectively prevented the resumption of meiosis and polymerization of periooplasmic microtubules. Furthermore, reversibility of the oocytes after reduced duration of BL I treatment was satisfactory.