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It has been recently proposed that a concomitant generation of oxidative stress of oocytes with increasing maternal age may be a major factor responsible for the age-related increase in aneuploid conceptions. As a preliminary step in the testing of this hypothesis, we need to confirm that oxidative stress in itself can induce errors in chromosome segregation. In order to achieve this goal, germinal vesicle (GV)-stage mouse oocytes from unstimulated ICR and (C57BL x CBA) F1 hybrid female mice were matured in vitro for 9 h for metaphase I (MI) oocytes or 16 h for metaphase II (MII) oocytes in the presence of varying concentrations of the oxidizing agent tertiary-butyl hydroperoxide (tBH). MII oocytes from (C57BL x CBA) F1 hybrid mice were fixed and C-banded for karyotyping analysis. MI and MII oocytes from ICR mice were fixed and stained with the DNA-fluorescent probe 4',6-diamidino-2-phenylindole (DAPI) to detect abnormalities in chromosomal distribution. Meiosis I and meiosis II spindles from ICR mice were visualized by confocal immunofluorescence microscopy. Data from these experiments demonstrate that in-vitro exposure of mouse oocytes to tBH during meiosis I reduces the length (pole-to-pole distance) and width (diameter at the equator of the spindle) of meiosis I and meiosis II spindles. This reduction is associated with an increase in the percentage of oocytes showing chromosome scattering and clumping on the MII plate, and of aneuploidy (hyperhaploidy) in MII oocytes. However, tBH at the concentrations used in the present study has only a minimal negative effect on the frequency of meiotic maturation. These results suggest that oxidative stress during meiotic maturation in vitro may induce chromosomal errors that are undetectable in the living oocyte and whose developmental consequences may become manifest after fertilization.

The oxidizing agent tertiary butyl hydroperoxide induces disturbances in spindle organization, c-meiosis, and aneuploidy in mouse oocytes