Time sequence of in vitro maturation and chromosomal normality in metaphase I and metaphase II of the squirrel monkey (Saimiri sciureus) oocyte.

Abstract

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.