Treatment with all-trans-retinoic acid decreases levels of endogenous TGF-β1 in the mesenchyme of the developing mouse inner ear

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Background: Previous studies have shown that in utero exposure of the mouse embryo to high doses of all-trans-retinoic acid (atRA) produces defects of the developing inner ear and its surrounding cartilaginous capsule, while exposure of cultured periotic mesenchyme plus otic epithelium to high doses of exogenous atRA results in an inhibition of otic capsule chondrogenesis. Methods: In this study, we examine the effects of atRA exposure on the endogenous expression of transforming growth factor-β1 (TGF-β1), a signaling molecule that mediates the epithelial-mesenchymal interactions that guide the development of the capsule of the inner ear. Results: Our results demonstrate a marked reduction in immunostaining for TGF-β1 in the periotic mesenchyme of atRA-exposed embryos of age E10.5 and E12 days in comparison with control specimens. Consistent with these in vivo findings, high-density cultures of E10.5 periotic mesenchyme plus otic epithelium, treated with doses of atRA that suppress chondrogenesis, showed significantly decreased levels of TGF-β1, as compared with TGF-β1 levels in untreated control cultures. Furthermore, we demonstrate a rescue of cultured periotic mesenchyme plus otic epithelium from atRA-induced chondrogenic suppression by supplementation of cultures with excess TGF-β1. Conclusions: Our results support the hypothesis that TGF-β1 plays a role in mechanisms of atRA teratogenicity during inner ear development. Teratology 61:297–304, 2000. © 2000 Wiley-Liss, Inc.