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Nocodazole sensitivity, age-related aneuploidy, and alterations in the cell cycle during maturation of mouse oocytes
1Lehrstuhl Gentechnologie/Mikrobiologie, Fakultät für Biologie, Universität Bielefeld, FRG.
Abstract:
To detect age-related alterations in the formation and function of the spindle apparatus, we examined in vitro maturing oocytes obtained from young (2-4 mo) and aged (greater than 9 mo) diestrous CBA/Ca mice. Observation of cells processed for antitubulin immunofluorescence revealed that oocytes from aged females progress faster through first maturation division than those from young animals. They are also more prone to nondisjunction, as shown by a significantly higher level of aneuploidy in C-banded cells arrested at metaphase II. The ability of oocytes to recover from treatment with a microtubule inhibitor, nocodazole, and the effect of the drug on spindle integrity and chromosome segregation were also studied. In both age groups, treatment of metaphase I oocytes with 10 microM nocodazole caused rapid and complete microtubule depolymerization and chromosome scattering. Upon recovery, oocytes from both age groups were able to reestablish a spindle apparatus, proceed through anaphase, and extrude a first polar body. However, nocodazole treatment led to a dramatic increase of aneuploidy. Unexpectedly, the relative rise in hyperploids was greater in oocytes from young mice than in those from aged mice, so that the absolute percentage of hyperploid metaphase II cells was similar in both age groups after drug treatment. Concomitantly, nocodazole exposure abolished or, at least, diminished intrinsic differences in the cell cycle and anaphase trigger present in the controls (e.g., the earlier onset of chromosome separation in oocytes from aged females). It shortened the period available for spindle formation before chromosome segregation in all oocytes. Therefore, our study implies that temporal differences in the progression of oocytes through maturation, in particular, the shortening of the time available for alignment of bivalents before chromosome separation occurs in oocytes of old females, are mainly responsible for age-related rises in aneuploidy. There is no indication that (1) the spindle apparatus of oocytes from aged mammals is more labile or susceptible to disturbances than the spindle apparatus of oocytes from young individuals or that (2) an increase in the number of univalents makes oocytes from aged mammals particularly prone to nondisjunction.
Insights
Aging female mice oocytes show increased aneuploidy due to faster maturation and reduced spindle formation time. This age-related increase in oocyte aneuploidy is linked to timing, not spindle apparatus fragility.
Area of Science:
- Reproductive Biology
- Cell Biology
- Genetics
Background:
- Age-related infertility is a growing concern, with oocyte quality declining significantly in older females.
- Oocyte maturation involves complex cellular processes, including spindle apparatus formation and chromosome segregation, which are critical for successful reproduction.
Purpose of the Study:
- To investigate age-related changes in the spindle apparatus formation and function during in vitro oocyte maturation.
- To determine the impact of aging on oocyte susceptibility to chromosome nondisjunction and aneuploidy.
Main Methods:
- Comparison of in vitro maturation of oocytes from young (2-4 months) and aged (greater than 9 months) CBA/Ca mice.
- Antitubulin immunofluorescence and C-banding techniques to analyze spindle apparatus and chromosome status.
- Assessment of oocyte recovery and aneuploidy induction following nocodazole treatment (microtubule inhibitor).
Main Results:
- Oocytes from aged mice exhibited faster progression through maturation and a higher incidence of aneuploidy (nondisjunction) at metaphase II.
- Nocodazole treatment induced aneuploidy in both age groups, with a similar absolute percentage of hyperploid cells post-treatment.
- Drug treatment abolished age-related differences in cell cycle progression, suggesting timing is crucial for chromosome segregation.
Conclusions:
- The primary cause of age-related aneuploidy in oocytes is the shortened time available for proper spindle formation and chromosome alignment in older females.
- The spindle apparatus in aged oocytes is not inherently more fragile or susceptible to disruption than in younger oocytes.
- Increased univalent formation does not appear to be a significant factor contributing to nondisjunction in aged oocytes.