The long-term objectives are to determine the relative contributions of the oocyte and the uterine environment to impaired fertility observed in older primates in natural cycles as well as reduced success in clinical in vitro fertilization (IVF) attempts. Age-related reduced fertility is becoming more important with general aging of the population and postponement of childbearing years. Case studies show that oocyte donation from younger women may reverse infertility in older women, whose oocytes may thus be inherently defective. Chromosome anomalies are more frequent in oocytes of older women but the true incidence of age-related chromosomal errors in fertilized oocytes and preimplantation embryos is unknown, and cannot be derived from examination of post-implantation tissues. This research will address age-related infertility in a controlled experimental setting without the limitations and ethical constraints of a clinical study. It will model the human situation using female rhesus monkeys: young (4-8 years), older (16-20 years; equivalent to women of 38-48 years) and aged (greater than or equal to 21 years old; equivalent to women 49+ years).
Specific aims are to determine: (1) the incidence of specific age-related chromosome anomalies in primate oocytes and in preimplantation embryos, and if these occur during oocyte (nuclear) maturation or during/after fertilization; (2) if oocytes from older primates have impaired ability to undergo nuclear maturation, fertilization, and/or timely embryonic development in vitro; (3) if ovarian gonadotropin stimulation increases frequencies of age-related chromosomal anomalies and exacerbates age-related impairments in nuclear maturation, fertilization and/or timely cleavage of preimplantation embryos; (4) if age-related chromosome anomalies are correlated with embryo developmental impairments. The study will thus attempt to correlate chromosome anomalies with preimplantation developmental defects, determine effects of maternal age on this relationship, and possible exacerbation by gonadotropin stimulation. Chromosome anomalies will be detected using fluorescent DNA probes for human chromosomes, which hybridize with homologous rhesus chromosomes. Specific rhesus chromosomes to be examined are 2, 16, 18, X and Y, because the most frequent human spontaneous abortions involve trisomy 16, trisomy 18, and monosomy X, while aberrations of large chromosomes like 2 are rarely detected in human post-implantation material. Young fertile males will be used for IVF-embryo development, avoiding confounding effects of male aging contributing to chromosomal and developmental errors. Because timeliness of embryo development is critical for viability, precise timing and morphological data on embryos derived from oocytes of young vs. older monkeys will be obtained by time lapse videomicroscopy, which maximizes information obtained from small numbers of oocytes/embryos. Key events, including pronuclear formation, cleavage, compaction, blastocele formation and zona pellucida hatching will be examined for significant timing and/or morphological anomalies. This study should provide insights into the etiology of preimplantation embryo losses, especially in older females.
| Schramm, R Dee; Paprocki, Ann Marie; Bavister, Barry D (2002) Features associated with reproductive ageing in female rhesus monkeys. Hum Reprod 17:1597-603 |
| Schramm, R D; Bavister, B D (1999) Onset of nucleolar and extranucleolar transcription and expression of fibrillarin in macaque embryos developing in vitro. Biol Reprod 60:721-8 |
