Expression and Action of Transforming Growth Factor Beta (TGFb1, TGFb2, and TGFb3) during Embryonic Rat Testis Development1

The objective of the current study was to determine the role of transforming growth factor beta (TGFb) during seminiferous cord formation and embryonic testis development. The expression pattern of mRNA for TGFb isoforms was evaluated during testis development through a quantitative reverse transcriptionpolymerase chain reaction (QRT-PCR) procedure. Expression of mRNA for TGFb1 was highest at postnatal day 0 (P0) and P10. In contrast, TGFb2 was high at embryonic day 15 (E15), declined at E16, and showed a transient increase at P0 through P3 of testis development. Interestingly, expression of mRNA for TGFb3 was high during embryonic development and then declined after P3. Immunohistochemical localization of TGFb1 and TGFb2 demonstrated expression in Sertoli cells at E14 and in the seminiferous cords at P0. Selective interstitial cells expressed high concentrations of TGFb1 and TGFb2 in P0 testis. TGFb3 was expressed in selective cells at the junction of the E14 testis and mesonephros. The cells expressing TGFb3 in the testis appeared to be preperitubular cells that resided around the seminiferous cords. TGFb3 was localized to gonocytes in P0 testis. TGFb1 was found to have no influence on seminiferous cord formation in embryonic organ cultures of E13 testis. In contrast, growth of both E13 and E14 embryonic organ cultures was inhibited by TGFb1 and resulted in reduced testis size (40% of controls) with fewer cords present. A P0 testis cell culture and thymidine incorporation assay were used to directly examine the effects of recombinant TGFb1. TGFb1 alone had no influence on thymidine incorporation in P0 testis cell cultures when compared to controls. Interestingly, TGFb1 inhibited epidermal growth factor (EGF), and 10% calf serum stimulated P0 testis cell growth but not FSH-stimulated growth. Therefore, TGFb1 appears to inhibit testis growth in both the embryonic and early postnatal periods. The hormonal regulation of TGFb expression was measured using P0 testis cell cultures and a QRTPCR procedure for each TGFb isoform. High concentrations of EGF stimulated expression of mRNA for TGFb1 after 24 h but suppressed expression of TGFb3. In contrast, there was no effect of FSH on TGFb isoform expression. In summary, TGFb regulates embryonic and P0 testis growth through inhibiting the actions of positive growth factors such as EGF. In addition, EGF but not FSH appears to regulate TGFb isoform expression. Combined observations from the present study demonstrate that TGFb isoforms are differentially expressed and appear to be regulators of testis growth during the embryonic and early postnatal periods.