Time Sequence of In Vitro Maturation and Chromosomal Normality in Metaphase I and Metaphase II of the Squirrel Monkey (Saimiri sciureus) Oocyte

The in vitro maturation sequence of squirrel monkey oocytes and their chromosomal normality was studied. Follicular growth was induced by a hormonal regimen of follicle-stimulating hormone (FSH) and human chorionic gonadotropin (hCG) and oocytes were collected laparoscopically 15–16 h after hCG administration from 55 squirrel monkeys. A total of 666 oocytes were prepared and analyzed for maturational stage and the presence of chromosomal aberrations.At recovery, 84.7% of the aspirated oocytes were in the genninal vesicle or prophase I stage and the numbers of atretic and mature ova were low (15.3% and 8.3%, respectively). The highest rate of in vitro matured oocytes (75.2%) was found after 31 h of incubation.In the chromosomal analysis studies of 366 oocytes, 31(8.5%) metaphase 1, 14 (3.8%) anaphase I and 181 (49.5%) metaphase II oocytes were examined. Of 28 countable metaphase I plates, 21 (75.0%) consisted of 22 bivalents, however meiotic univalents were also observed in 7 (25.0%) cases. Of these, 2 showed a secondary association.Of 181 oocytes, 145 (80.1%) were analyzable numerically. Of these, 88 (60.7%) had the normal haploid 22 chromosome number, whereas 7 (4.8%) showed aneuploidy (4 hyperploidy and 3 hypoploidy). An additional 50 (34.5%) oocytes were found to be at the metaphase II stage with first polar body chromosomes. Of these, 43 had a normal haploid number of chromosomes (22/22). In 7 (4.8%), aneuploidy was observed (6, 21/23 and 1, 20/24). The unequal chromosome number was assumed to be due to a random segregation of univalents at the anaphase I stage.Additionally there was no significant difference in maturation rate among 3 sizes of follicles (1–2 mm, 2–3 mm, >3 mm). A significant correlation was found for the maturation rate between oocytes with and without cumulus cells after 21 h of culture.