Xenopus laevis: a model system for the study of embryonic retinoid metabolism. I. Embryonic metabolism of 9-cis- and all-trans-retinals and retinols to their corresponding acid forms.

Recently, the temporal and spatial distribution patterns of two established, endogenous retinoid receptor ligands, 9-cis-retinoic acid and all-trans-retinoic acid and various precursor retinoids were described in Xenopus embryos during early development (Creech Kraft et al., Proc. Natl. Acad. Sci. U.S.A. 1994; Biochem. J. 1994). Each of these two receptor ligands is a metabolite of vitamin A (all-trans-retinol), and each is also a potent dysmorphogen in Xenopus embryos as well as in embryos of several other vertebrate species. This study demonstrates early embryonic metabolism of exogenous all-trans-retinol, 9-cis-retinol, all-trans-retinal, and 9-cis-retinal to 9-cis-retinoic acid, all-trans-retinoic acid, and other metabolites in Xenopus embryos during neurulation, a specific stage of development that spans a time period of approximately 8 hr. Our results demonstrate that the Xenopus embryo provides a suitable model system for studying the embryonic bioconversion of retinoids and dysmorphogenic effects within a single time window of development.