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 (RARα, RARβ, RARγ) 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 RARα-selective antagonist had no effect. RT-PCR demonstrated that RARα messenger RNA (mRNA) was expressed at all developmental time points evaluated, which included embryonic day 14 (E14) through postnatal day 30 (P30). Expression of RARβ mRNA was present at E15 through P2, whereas RARγ mRNA was expressed at E18 through P2. Cellular localization of receptors by immunohistochemistry indicated that RARα was localized to the interstitium at E18 and to the seminiferous cords by P0. RARβ and RARγ were detected in both interstitium and cords at E16 and by E18 were mainly expressed in the cords. At P0 RARβ and RARγ 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-β (TGFβ). The action of retinoids on TGFβ mRNA expression was examined in P0 testis cultures. Retinoic acid stimulated TGFβ3 mRNA expression within 24 h and increased expression of TGFβ1 and TGFβ2 after 72 h. Retinol increased expression of TGFβ1 and TGFβ2 but not TGFβ3 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 TGFβ isoforms.
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