EPIDERMAL GROWTH-FACTOR AND TRANSFORMING GROWTH-FACTOR-BETA MODULATION OF FOLLICLE-STIMULATING HORMONE-INDUCED DEOXYRIBONUCLEIC-ACID SYNTHESIS IN HAMSTER PREANTRAL AND EARLY ANTRAL FOLLICLES

The interactions of epidermal growth factor (EGF) and transforming growth factor-beta (TGF-beta) in modulating FSH-induced follicular DNA synthesis were studied in isolated intact preantral (stages 1-6) and early antral (stage 7) ovarian follicles from adult hamsters. Follicles were exposed in vitro for 24 h to FSH (100 ng), EGF (50 ng), TGF-beta1 (1-10 ng), or TGF-beta2 (1-10 ng), either alone or in combination. The rate of DNA synthesis was assessed by measuring the incorporation of [H-3]thymidine into follicular DNA. Both EGF and FSH significantly stimulated follicular DNA synthesis compared with that in controls. Both isoforms of TGF-beta significantly increased follicular [H-3]thymidine incorporation in a dose-dependent manner; the effect was greater for small preantral follicles, such as those of stages 1-4. Interestingly, TGF-beta significantly inhibited EGF-induced follicular DNA synthesis, but the rates of DNA synthesis for most of the stages were still higher than that of dic control follicles. Specificity of the TGF-beta action on follicular DNA synthesis was evident from the ability of isoform-specific anti-TGF-beta antibodies to neutralize the effect. These antibodies also reversed the TGF-beta inhibition of EGF-induced DNA synthesis. Surprisingly, although TGF-beta attenuated EGF-induced DNA synthesis, it synergized with FSH to stimulate follicular DNA synthesis. Interestingly, FSH-induced DNA synthesis remained unaffected by the anti-TGF-beta antibodies, indicating that TGF-beta may not mediate FSH action on follicular DNA synthesis. These studies suggest that a critical interaction of EGF and TGF-beta modulates granulosa cell proliferation during folliculogenesis in the hamster. TGF-beta may also influence FSH regulation of cell proliferation by lengthening the G1 phase of the granulosa cell cycle, thus recruiting more cells to enter the S phase when the preovulatory FSH surge acts on growing follicles.