Oocyte maturation.

The oocyte is dependent on granulosa cells to provide nutrients and regulatory signals. Granulosa cells must be at the appropriate stage of differentiation to initiate these signals and transmit them to the oocyte. Studies have shown that in vitro-matured oocytes from follicles in early stages of atresia are more competent to support embryonic development than those from actively growing follicles. The acquisition of developmental competence appears to occur prior to in vitro maturation and can be induced by gonadotropin-free coasting in vivo or postmortem ovary incubation in vitro. The acquisition of developmental competence is probably a common signaling or differentiation pathway that occurs in the oocyte and/or associated granulosa regardless of whether the oocyte is destined to ovulate or degenerate. Early follicle atresia is the visually discernible characteristic in vitro that is associated with increased developmental potential.