ABSTRACT
Oocyte aneuploidies are increased with advancing age in human and these aneuploidies are associated with maternal ageing and result from non-disjunctions and meiotic errors. The objective of this work was to use mouse as a model to study the effect of aging on chromosome and spindle disorganizations in MI and MII CBA/Caj mouse oocytes. Mice were divided to young, [3 months] and aged, [8 months] groups and Swiss Webster mice were used as a double control. The animals were superovulated and the oocytes were retrieved in FHM medium 16h after HCG injection. Immature [MI] and mature [MII] ovulated oocytes were recovered from ampulla and fixed, washed in block-wash solution. Spindle microtubules and chromosomes were visualized using immunofluorescent microscopy with anti beta tubulin monoclonal antibodies and staining with propidium iodide, respectively. The chromosome disorganization rate in MI young oocytes was lower than MII oocytes. The correlation between chromosome and spindle disorganizations was significantly higher in MI and MII oocytes [P<0.05] compared to control. The percentage of the MII oocytes was significantly higher [P<0.01] compared to MI oocytes in the young group but this was not the case in the aged group. This may indicate that the oocyte maturation mechanism was affected adversely by ageing process. In conclusion, the positive correlation between chromosome and spindle disorganizations in MI and MII oocytes may be an indicator for embryo aneuploidy. Ageing induced an increase in the production of ovulated MI versus MII oocytes. CBA/Caj mouse may be used as animal model for study ageing effect on reproductive system