Atretic changes of follicular wall caused by destruction of the germinal disc region of an immature preovulatory follicle in the chicken: an electron microscope study.

The germinal disc of the female gamete and its overlying follicular wall (the germinal disc region) is hypothesized to play an important role in the regulation of follicular growth. The role of the germinal disc region in follicular growth in chickens was investigated by destroying the germinal disc region or an area opposite the germinal disc (control) of the second largest follicle 22-23 h before ovulation of the F1 follicle, by localized freezing with solid CO2. Structural changes of the follicular wall (non-frozen region) were observed by electron microscopy 10-20 h after the destruction of the germinal disc region. Development of the inner structure of mitochondria in granulosa cells and accumulation of lipid droplets in thecal cells were observed in follicles 15 h after destruction of the germinal disc region. Twenty hours after destruction of the germinal disc region, follicles showed early signs of atresia (bursting atresia). Degenerative changes in follicles, including hydrolysis by lysosomal enzymes, were present in thecal fibroblast-like cells. Control follicles, in which an area opposite the germinal disc region was frozen 20 h before examination, had no degenerative features. These results provide further evidence that the germinal disc region is required for follicular growth.