Abstract
Enzymatic dispersed small naked mouse oocytes from ovaries at birth were co-cultured with ovarian somatic cells for eight days in vitro, and the growth of oocytes and the formation of zona pellucida were examined. After enzymatic treatment of the ovaries at birth (Day 0 of culture), oocytes and ovarian cells were dispersed completely. The oocytes were 11-22 μm in diameter (average: 16.9±2.2 μm) and had no zona pellucida around them. From Day 1 of culture, oocytes and ovarian somatic cells aggregated, formed several clumps and oocytes grew inside or became attached to them. On Days 4, 6 and 8 of culture, 3.0, 6.0 and 35.3% of oocytes grew to 30 μm or more in diameter, respectively. Even on Day 8 of culture, no follicle formation was observed. At the periphery of the grown oocytes without surrounding somatic cells on the clumps, PAS-positive, indented zona pellucida-like materials were deposited. The materials reacted strongly with anti-mouse zona pellucida antibody in immunogold staining. Immuno-reactive materials were also observed in the oocyte cytoplasm, whereas no reaction was found in ovarian somatic cells. These results suggest that the zona pellucida was formed by the oocyte and deposited its periphery without follicle formation in mice.
