XENOPUS-LAEVIS - A MODEL SYSTEM FOR THE STUDY OF EMBRYONIC RETINOID METABOLISM .1. EMBRYONIC METABOLISM OF 9-CIS-RETINALS AND ALL-TRANS-RETINALS AND RETINOLS TO THEIR CORRESPONDING ACID FORMS

Recently, the temporal and spatial distribution patterns of two establ ished, endogenous retinoid receptor ligands, 9-cis-retinoic acid and a ll-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 r eceptor ligands is a metabolite of vitamin A (all-trans-retinol), and each is also a potent dysmorphogen in Xenopus embryos as well as in em bryos of several other vertebrate species. This study demonstrates ear ly embryonic metabolism of exogenous all-trans-retinol, 9-cis-retinol, all-trans-retinal, and 9-cis-retinal to 9-cis-retinoic acid, all-tran s-retinoic acid, and other metabolites in Xenopus embryos during neuru lation, a specific stage of development that spans a time period of si milar to 8 hr. Our results demonstrate that the Xenopus embryo provide s a suitable model system for studying the embryonic bioconversion of retinoids and dysmorphogenic effects within a single time window of de velopment.