Contractile microfilaments in granulosa cells. An ultrastructural and immunochemical study.

Electron microscope observations demonstrated bundles of microfilaments measuring 40-70 A in diameter in the granulosa cells of normal developing follicles of rabbit ovary. The microfilaments appeared concentrated in the cortical areas of the cytoplasm and within large evaginations and microvilli. In addition the filaments were particularly abundant in the granulosa cells of corona radiata and free cells in the cavity. Immunofluorescent staining on frozen sections of rabbit ovary demonstrated that the granulosa cells of developing follicles bind antimyosin-like antibodies (AMA). Considering the correspondence between the immunochemical and ultrastructural fingings it is suggested that the microfilaments contain a "myosin-like" protein. It seems then reasonable to suggest that the ovarian follicles are not kinetically passive organs, but they contain contractile filaments for their specific functions.