Orchestrated expression of steroidogenic side-chain cleavage cytochrome P-450 during follicular development in the rat ovary.

Antibody to the mitochondrial cholesterol side-chain cleavage cytochrome P-450 (P-450scc) was used to study the expression of this key steroidogenic enzyme during follicular development. Immunofluorescence staining of tissue cryosections and isolated cells revealed unique and cell-specific patterns of P-450scc expressed in four cell types of the prepubertal rat ovary. Without hormonal treatment, the interstitial gland expressed ample amounts of P-450scc. Within 24 h after PMSG administration, theca interna acquired the cytochrome, and after an additional 24 h, the enzyme appeared also in granulosa cells. However, expression of P-450scc in granulosa cells was observed only in preovulatory follicles. This was in contrast to the theca interna cells which differentiated in various follicles unrelated to their stages of development. Cumulus cells were the last cell type to express P-450scc, occurring as late as 2-3 h before ovulation. These observations indicate that the concerted expression of P-450scc in the different ovarian cell types is a well-timed phenomenon which is precisely co-ordinated during follicular development.