A peptidyl-prolyl isomerase, Pin1, has been shown to play a role in the regulation of cell cycle progression, both in vitro and in vivo. However, the involvement of Pin1 during follicular development is not well understood. The aim of this study was first to investigate the expression of Pin1 mRNA in the granulosa and theca cells of the follicle at different developmental stages of follicles in the bovine ovary, and second, to examine the effects of follicle-stimulating hormone (FSH) and estradiol (E2) on the expression of Pin1 in the cultured bovine granulosa cells. Follicles were classified into four groups based on the diameter (dominant follicles >8.5 mm in diameter, subordinate follicles <8.5 mm in diameter) and the relative levels of E2 and progesterone (P4) (E2:P4 > 1, estrogen active; E2:P4 < 1, estrogen inactive): i.e. preovulatory dominant follicles (POFs); E2 active dominant follicles (EADs); E2 inactive dominant follicles (EIDs); small follicles (SFs). The expression of the Pin1 gene was significantly increased in the granulosa cells of EADs as compared with those of other follicles, whereas its expression in theca cells did not differ among follicles at different developmental stages. The concentration of 5 ng/ml FSH alone and the combination of 1 ng/ml E2 and 5 ng/ml FSH stimulated the expression of the Pin1 gene in bovine granulosa cells. Our data provide the first evidence that Pin1 expression in the granulosa cells but not the theca cells changes during follicular development, and that FSH stimulate the expression of the Pin1 gene. These results suggest that Pin1 regulates the timing of cell proliferation and may act as an intracellular signal responder in the granulosa cells during bovine follicle development.
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