Transcriptomics analysis of retinoic acid embryotoxicity in rat postimplantation whole embryo culture.

Rodent postimplantation whole embryo culture (WEC) is a classical alternative test to study developmental toxicants. Here, we have successfully applied transcriptomics to monitor early responses in WEC after exposure to the embryotoxicant retinoic acid (RA). We demonstrated that RA exposures ranging from 2 to 24h affect RA-responsive genes in individual embryos. Furthermore, 2, 3 or 4 somite embryos gave similar responses, allowing combining embryos of these embryonic stages within the same analysis. Microarray analysis of embryonic gene expression after RA exposure revealed the regulation of many genes known to be RA responsive. Finally, use of a culture medium based on bovine serum instead of rat serum yielded similar gene expression responses after RA exposure. These findings support the robustness of the identified gene expression patterns and show the feasibility of detecting early gene expression changes in WEC after embryotoxic exposures. This approach may result in a more sensitive readout for detecting embryotoxicity in WEC.

Embryotoxicant-specific transcriptomic responses in rat postimplantation whole-embryo culture.

Rat postimplantation whole-embryo culture (WEC) is a promising alternative test for the assessment of developmental toxicity. Toxicogenomic-based approaches may improve the predictive ability of the WEC model by providing a means to identify compound-specific mechanistic responses associated with embryotoxicity in vivo. Furthermore, alterations in gene expression may serve as a sensitive, objective, and robust marker, which precedes the observation of classical developmental toxicity endpoints in time. In this study, in combination with morphological developmental assessments, we studied transcriptomic responses associated with four distinct teratogens (caffeine [CAF], methylmercury [MM], monobutyl phthalate, and methoxyacetic acid) after 4 h of exposure, well before apparent embryotoxicity in WEC. We evaluated gene expression changes associated with similar levels of induced morphological embryotoxicity for each teratogen (as determined by total morphological score), evaluating for functional enrichment and quantitative changes in response. Concentrations selected for each of the four teratogens used induced a number of common effects on embryonic development (neural tube closure and optic/otic system). Despite inducing common morphological effects, our analysis suggests limited overlap in terms of toxicogenomic response at the gene expression level and at the level of biological processes across all four test chemicals. Many unique responses associated with each chemical correlated with previously hypothesized modes of developmental toxicity. For example, alterations in developmental signaling and cholesterol metabolism were observed with MM and CAF, respectively. This initial study suggests that distinct chemically induced toxicogenomic responses precede morphological effects in WEC and that these responses are relevant with mechanisms of toxicity previously observed in vivo.