Transforming growth factor beta 3 in the fetal and neonatal rat testis: immunolocalization and effect on fetal Leydig cell function

The localization of transforming growth factor beta 3 (TGF beta 3) in the f etal and neonatal testis (from fetal day 13.5 to postnatal day 6) was inves tigated by immunohistochemical staining with a specific polyclonal antibody raised against a synthetic peptide corresponding to residues 50-75 of TGF beta 3. This antibody recognized 0.5 ng TGF beta 3 in western blot analysis , but did not detect 25 ng TGF beta 1 or TGF beta 2. The immunolocalization of TGF beta 3 in the fetal and neonatal testis changed throughout developm ent. Immunostaining was present in the gonocytes by fetal day 13.5, persist ed until postnatal day 3, and was heterogeneous in spermatogonia on postnat al day 6. The Sertoli cells contained no immunoreactivity at any age. The f etal-type Leydig cells were first immunostained for TGF beta 3 on day 16.5 and staining became very intense from day 18.5 onward. Staining disappeared when the antibody was presaturated with the synthetic peptide, but persist ed when the antibody was presaturated with a tenfold excess of the correspo nding peptide from TGF beta 2. Furthermore, we researched whether TGF beta 3 could act as a local regulator of fetal Leydig cell function. In a disper sed fetal testicular cell system, TGF beta 3 inhibited the LH-stimulated te stosterone production by Leydig cells from 20.5-day-old fetuses. The inhibi tory effect of TGF beta 3 was equal to that observed with TGF beta 1 or TGF beta 2. When compared with our previous studies showing the immunolocaliza tion of TGF beta 1 and TGF beta 2, the present study shows that TGF beta 3 may have a specific role in the developing rat testis, but may also overlap the action of TGF beta 1 and TGF beta 2.