Action of retinoids on embryonic and early postnatal testis development

The current study investigates the hypothesis that retinoids have a role in embryonic testis development. The action of retinoids on testis development and the expression of retinoic acid receptors (RAR alpha, RAR beta, RAR gamma) were examined. In embryonic day 13 (E13; plug date = E0) testis organ cultures an RAR-selective agonist and all-trans retinoic acid completely inhibited seminiferous cord formation. In contrast, an RAR alpha-selective antagonist had no effect. RT-PCR demonstrated that RAR alpha messenger RNA (mRNA) was expressed at all developmental time points evaluated, which included embryonic day 14 (E14) through postnatal day 30 (P30). Expression of RAR beta mRNA was present at E15 through P2, whereas RAR gamma mRNA was expressed at E18 through P2. Cellular localization of receptors by immunohistochemistry indicated that RAR alpha was localized to the interstitium at E18 and to the seminiferous cords by P0. RAR beta and RAR gamma were detected in both interstitium and cords at E16 and by E18 were mainly expressed in the cords. At P0 RAR beta and RAR gamma were localized to the germ cell populations. To examine retinoid actions, the growth of P0 testis cultures were investigated. Interestingly, retinol and retinoic acid did not inhibit growth of P0 testis cultures but did inhibit the action of growth stimulators. Retinoic acid inhibited FSH, EGF, and 10% calf serum stimulated growth in P0 testis cultures. The hypothesis tested was that the inhibitory effects of retinoids on P0 testis growth may be mediated through the growth inhibitor, transforming growth factor-beta (TGF beta). The action of retinoids on TGF beta mRNA expression was examined in P0 testis cultures. Retinoic acid stimulated TGFbeta3 mRNA expression within 24 h and increased expression of TGFbeta1 and TGFbeta2 after 72 h. Retinol increased expression of TGFbeta1 and TGFbeta2 but not TGFbeta3 after 72 h of treatment. These observations indicate that retinoic acid can influence seminiferous cord formation and testis growth. The inhibitory actions of retinoids may in part be mediated through increased expression of TGFbeta isoforms.