Ultrastructure and some biologic properties of human oocytes and granulosa cells cultured in vitro.

Of follicular oocytes with germinal vesicles, 79% resumed meiosis within 48 hours in modified Ham's F-10 medium for oocyte culture, and 59% of them reached the second-metaphase stage of meiosis. An increase in cortical granules and tubular aggregates and a decrease in the Golgi apparatus were observed during the maturation process. Scanning electron microscopy of the oocyte surface revealed a decrease in number and length of microvilli. Nuclear DNA contents diminished to approximately one-half, but cytoplasmic protein contents measured by cytofluorometry were unchanged after culture in spite of these structural changes. Insemination with washed spermatozoa resulted in fertilization of 5 of 43 zona-intact cultured oocytes. After removal of the zona, 6 of 17 cultured oocytes showed polyspermic penetration, although immature oocytes were not fertilized even after removal of the zona. Cultured granulosa cells secreted progesterone spontaneously, and its amount was correlated with follicular size. Ultrastructurally, mitochondria with laminar cristae, enlarged nuclei, dispersed Golgi apparatus, smooth endoplasmic reticulum, lipid droplets in the ooplasm, and granular cytoplasmic protrusions were observed on the oocyte surface.