The expression of cytoskeletal proteins during the differentiation of rat granulosa cells.

This report examines the relationship between aromatase activity and progesterone production and the expression of actin and vinculin in rat granulosa cells, exposed to insulin, follicle stimulating hormone (FSH) and human chorionic gonadotrophin (HCG). Granulosa cells of pre-antral follicles from juvenile rats treated with diethylstilbestrol (DES) were cultured on collagen A-coated plastic coverslips in serum-free medium. At a moderate or low level of steroidogenesis (FSH alone), the expression of vinculin was diminished while vinculin plaques disappeared completely. At a high level of steroidogenesis (both FSH and insulin), actin in stress fibre form was also decreased considerably. Under conditions of progesterone production (pretreatment with FSH and subsequent incubation with HCG), a concomitant increase of actin in soluble form was found. It is concluded from these studies that the higher the steroidogenesis level of the granulosa cells, the lower the organization of the microfilaments vinculin and actin, which are regulated independently of each other.