252 EFFECTS OF IN VITRO MATURATION AND AGE ON OOCYTE METAPHASE SPINDLE INTEGRITY AND CHROMOSOME SEGREGATION IN THE RHESUS MONKEY

Abstract

Oocyte IVM offers tremendous potential for the treatment of infertility by reducing the costs, risks, and side effects associated with ovarian stimulation. Although normal offspring have been produced using IVM/IVF technology in humans and monkeys, IVM is far from being a reliable technique for the production of developmentally competent oocytes in primates. This study examined oocyte karyotype and spindle integrity in rhesus monkey oocytes, and attempted to correlate anomalies with IVM and age of oocyte donors. Each of 14 females (ages 6 to 22 years) underwent both regimen A (FSH + hCG) and regimen B (FSH only) stimulation cycles at least once over the study period to facilitate collection of both mature and immature oocytes. Immature oocytes from regimens A and B underwent IVM to produce metaphase II oocytes. Metaphase II oocytes from each collection cycle cohort were fixed for either karyotype or metaphase spindle analysis. Statistical analysis of aneuploidy rates and spindle aberrations was performed using 2 × 2 G tests. Karyotype analysis revealed a significantly lower rate of aneuploidy in in vivo-matured (IVO) oocytes (6.0%) compared with IVM oocytes from regimen B (19.8%). Factoring age into these analyses revealed a significant difference in aneuploidy rate between IVO oocytes from young females (4.7%) and regimen B IVM oocytes from old females (25.0%; P < 0.05). Confocal analysis demonstrated a significant increase in metaphase spindle anomalies in IVM oocytes compared with IVO oocytes, which could be attributed to a significant increase in the rate of abnormal chromosome alignment on the metaphase spindle in IVM oocytes originating from either stimulation regimen: 7.0% in IVO oocytes v. 27.9% (regimen A) and 32.6% (regimen B) in IVM oocytes (P < 0.05). When donor female age was considered, regimen B IVM oocytes from old females displayed abnormal chromosome alignment on the spindle equator at a significantly higher rate than oocytes of any other maturation condition or age group (P < 0.05). In addition, IVO oocytes from young females showed this anomaly at a significantly lower rate than regimen B IVM oocytes from the same young females. We conclude that IVM can induce meiotic anomalies in the macaque oocyte, especially those obtained from older females. The results from this study provide possible explanations for the reported reduction in developmental competence of IVM v. IVO primate oocytes. This study provides information on the nuclear aspects of IVM, namely, the effect of maturation conditions and age on incidences of abnormal chromosome segregation during meiosis I and abnormal chromosome congression during meiosis II, data that may be helpful for determining optimal IVM culture conditions.