Abnormalities of forelimb and pronephros in a direct developing frog suggest a retinoic acid deficiency

The direct developing frog, Eleutherodactylus coqui, serves as a model for a divergent, derived pattern of anuran development. Reproduction and development occur normally in captivity, although individual embryos and sometimes entire clutches exhibit edema. Edematous embryos have abnormal pronephroi, as judged by histology and by alkaline phosphatase staining. The pronephric defects would be sufficient to account for the edema. The first indicator of later edema is loss or reduced development of the forelimbs. The coupling of forelimb and pronephric abnormalities is likely due to insufficient retinoic acid. The same syndrome can be produced experimentally by treatment with citral, an inhibitor of retinoic acid synthesis. The involvement of retinoic acid in forelimb development. found previously in other vertebrates, can now be extended to anuran amphibians. Reduced forelimb development in embryos may be a useful way to detect insufficient dietary vitamin A in reproductive colonies of direct developing frogs and of other vertebrates.