Effects of follicle size and oocyte maturation conditions on maternal messenger RNA regulation and gene expression in rhesus monkey oocytes and embryos.

The relationship between alterations in gene expression and differences in developmental potential in primate oocytes and embryos was examined. Oocytes from 3 sources were used for these studies: 1) in vivo-matured oocytes from monkeys stimulated with FSH and hCG, 2) in vitro-matured oocytes from large follicles of monkeys primed with FSH, and 3) in vitro-matured oocytes from small follicles from nonstimulated (NS) monkeys. Following in vitro fertilization, embryos from these oocytes displayed high, moderate, and low developmental competence, respectively. Oocytes from NS females displayed aberrant accumulation of a number of maternal mRNAs, followed by precocious loss of many maternal mRNAs by the 2-cell stage. Embryos from NS oocytes displayed alterations in expression of key transcription factors after the 8-cell stage. Oocytes and embryos from FSH-stimulated females also displayed alterations in gene expression relative to hCG-stimulated females, but these alterations were much less severe than those observed for NS oocytes and embryos. Our data are consistent with the hypothesis that continued development and maturation of the oocyte within the ovarian follicle in vivo facilitates the production of oocytes of the highest developmental potential, and that in vitro conditions may not support this process as effectively due to differences in the extracellular milieu. These observations are relevant to understanding the role of the in vivo environment on oocyte maturation, and the potential effects of in vitro maturation on human assisted reproduction methods.