Diethylstilbestrol (DES)-induced cell cycle delay and meiotic spindle disruption in mouse oocytes during in-vitro maturation

Due to the growing amount of data related to the deleterious effects of the synthetic oestrogenic compound, diethylstilbestrol (DES), on the female reproductive system, we tested the potential effects of this compound on mouse oocytes. Controlled time- and dose-dependent in-vitro experiments were carried out on isolated cumulus-oocyte-complexes (COCs) to examine the meiotic spindle assembly and chromosome distribution. alpha-tubulin, chromosomes and F-actin were labelled and detected by confocal laser scanning microscope. COCs were exposed to varying doses of DES 1530 mu mol/l from the germinal vesicle (GV) stage to the end of metaphase II (MII) when meiosis I and meiosis II is normally completed. Exposure to DES during meiosis I caused a dose-dependent inhibition of cell cycle progression. In comparison with controls, Fewer oocytes reached metaphase I (MI) at low doses (5 mu mol/l) of DES, while none of the oocytes reached MI in high doses (30 mu mol/l). When COCs were exposed to high doses of DES during meiosis II, fragmentation of first meiotic spindle was detected, whereas lower doses caused loosening of the first and the second meiotic spindles. No microtubular abnormalities were detected either in GV-stage oocytes or in cumulus cells. The above data demonstrate that one mode of action of DES on mouse oocytes is a severe yet reversible deterioration of meiotic spindle microtubule organization during maturation.