A Comparison of Gene Expression Responses in Rat Whole Embryo Culture and In Vivo: Time-Dependent Retinoic Acid-Induced Teratogenic Response

The whole embryo culture (WEC) model serves as a potential alternative for classical in vivo developmental toxicity testing. In the WEC, cultured rat embryos are exposed during neurulation and early organogenesis and evaluated for morphological effects. Toxicogenomic-based approaches may improve the predictive ability of WEC by providing molecular-based markers associated with chemical exposure, which can be compared across multiple parameters (e.g., exposure duration, developmental time, experimental model). Additionally, comparisons between in vitro and in vivo models may identify objective relevant molecular responses linked with developmental toxicity endpoints in vivo. In this study, using a transcriptomic approach, we compared all-trans retinoic acid (RA)-exposed and nonexposed Wistar rat embryos derived using WEC (RA, 0.5 mu g/ml) or in vivo (RA, 50 mg/kg, oral gavage) to identify overlapping and nonoverlapping effects of RA on RNA expression in parallel with morphological changes. Across six time points (gestational day 10 + 2-48 h), we observed strong similarities in RA response at the gene (directionality, significance) and functional (e.g., embryonic development, cell differentiation) level which associated with RA-induced adverse morphological effects, including growth reduction as well as alterations in neural tube, limb, branchial, and mandible development. We observed differences between models in the timing of RA-induced effects on genes related to embryonic development and RA metabolism. These observations on the gene expression level were associated with specific differential morphological outcomes. This study supports the use of WEC to examine compound-induced molecular responses relative to in vivo and, furthermore, assists in defining the applicability domain of the WEC in determining complementary windows of sensitivity for developmental toxicological investigations