The association between the oocyte pool and aneuploidy: a comparative study of the reproductive potential of young and aged mice

The present study examined the effect of aging on female reproductive potential. Six-week-old and 9-month-old CD1 mice were referred to as the 'young' and 'aged' groups, respetively. Oocytes were collected after superovulation, and their viability were compared using parthenogenetic activation. The aneuploidy of the oocytes (MII) was assessed using chromosome spread, and the whole ovarian follicle number was counted using an unbiased stereological method. Serum hormone levels were measured using the radio-immunity method, and the expression of the Cohesin subunit genes in the oocytes (GV) were assessed using RT-PCR. The mean number of recovered (25.8 vs. 16.2; P < 0.05) and live oocytes (24.0 vs. 11.73; P < 0.01) per head in the young-mice group (6-week-old) was significantly higher than that of the aged group (9-month-old). The aneuploidy rate of the ovulated oocytes in the aged group was significantly higher than that of the young group (36.8 % vs. 10 %; P < 0.01), and the rate of blastocyst formation in the young group (85.23 %) was significantly higher than that of the aged group (81.2 %; P < 0.05). The number of primordial follicles (the oocyte pool) per ovary in the aged group was significantly decreased compared with the young group (330 +/- 33.51 vs. 2079.6 +/- 420.70; P < 0.01), and the level of AMH in the aged group was significantly higher than that of the young group (4.66 +/- 0.11 ng/ml vs. 4.07 +/- 0.18 ng/ml; P < 0.01). We propose that maternal aging significantly reduces the oocyte pool, superovulation efficiency and developmental potential and increases the oocyte aneuploidy rate.