Differential localization of inhibin subunit proteins in the ovine testis during fetal gonadal development

Inhibins and activins are dimeric proteins that are involved in cell prolif eration, apoptosis, and differentiation in a number of systems and have pre viously been detected in fetal testes of many species. This study used immu nohistochemistry to examine the localization of inhibin alpha-, beta(A)-, a nd beta(B)- Subunits during ovine testicular development fi om days 40-135 of gestation. Localization of inhibin beta(A)- and beta(B)-subunit messenge r RNAs was confirmed by in situ hybridization. The results showed that there was differential localization of inhibin alph a-, beta(A), and beta(B)-subunits to specific cells in the ovine fetal test is from 40 days of gestation. All three inhibin subunits were present in Se rtoli cells throughout gestation, whereas the rete epithelium and gonocytes did not express inhibin alpha-subunit. These data suggest that the fetal S ertoli cells have the capacity to produce all forms of inhibins and activin s, i.e. inhibin A and B, and activins A, AB, and B, whereas the rete testis epithelial cells can only synthesize activin A. In the interstitium, the f etal Leydig cells expressed all three inhibin subunits, but this was restri cted to the period between 40 and 90 days of gestation. Thereafter, inhibin ru-subunit immunoreactivity was not observed in fetal Leydig cells, which suggests that only activin Ligands are produced by Leydig cells during late gestation. Collectively, the data demonstrate that fetal ovine testes have the potenti al to produce the full repertoire of inhibins and activins hom very early i n testicular differentiation. The distinct and restricted localization of t he various subunits to specific cells suggests that specific dimeric protei ns have particular roles in the development and function of the fetal testi s.