TRANSFORMING GROWTH-FACTOR-BETA POTENTIATION OF FOLLICLE-STIMULATING HORMONE-INDUCED DEOXYRIBONUCLEIC-ACID SYNTHESIS IN HAMSTER PREANTRAL FOLLICLES IS MEDIATED BY A LATENT INDUCTION OF EPIDERMAL GROWTH-FACTOR

The mechanisms of transforming growth factor-beta (TGF-beta) potentiation of FSH action on follicular DNA synthesis in the hamster were investigated by use of TGF-beta (beta1 and beta2) and a potent epidermal growth factor (EGF)-specific polyclonal antibody. Preantral follicles at stages 1-6 and early antral follicles at stage 7 were enzymatically and mechanically isolated from adult golden hamsters on proestrus. Follicles were incubated in Dulbecco's modified Eagle's medium with ITS+ (6.25 mug insulin, 6.25 mug transferrin, 6.25 mug selenium, 1.25 mg BSA, and 5.35 mug linoleic acid/ml) hydrocortisone, and 1 muCi/ml [H-3]thymidine. Follicles were exposed for 24 h to FSH (100 ng/ ml), TGF-beta1, and TGF-beta2 (1 and 10 ng/ ml), EGF antibody (50 mul/ml), and TGF-alpha (50 ng/ml) under various experimental conditions. Both TGF-beta1 and TGF-beta2 significantly potentiated FSH-induced follicular DNA synthesis; however, the effect was drastically attenuated by EGF antibody. EGF antibody also inhibited FSH-induced folliCUlar [H-3]thymidine incorporation. TGF-beta2 potentiation of FSH action was also significantly inhibited by a second dose of TGF-beta2 when added 6 h after the beginning of culture; however, follicles at different stages responded differently to the second dose of TGF-beta2. For example, when the second dose of TGF-beta2 was added 14 h after the first dose, only the large preantral follicles at stages 4-6 were affected. Interestingly, the second dose of TGF-beta2 also inhibited TGF-beta2-induced DNA synthesis. The inhibitory effect of EGF antibody on TGF-beta2 and FSH synergism was effectively reversed by TGF-alpha, which was not recognized by the EGF antibody. These results suggest that TGF-beta potentiation of FSH-induced follicular [H-3]thymidine incorporation involves a latent action of follicular EGF. TGF-beta appears to lengthen the G1 phase of the follicular cell cycle and synchronize a significantly higher number of cells at the G1/S boundary, thus allowing more cells to enter the S phase and a resultant increase in net [H-3]thymidine incorporation.