In the present study, the authors investigated the effects of bisphenol A, chlorpyrifos, methylparaben, and 2 effluent samples from wastewater treatment plants located in the province of Madrid, Spain, on the messenger RNA expression of specific genes involved in early development (ESR1, pax6, bmp4, and myf5) and a gene involved in the general stress response (hsp70) during Xenopus laevis embryo development. Gene expression was analyzed after 4 h, 24 h, and 96 h of exposure by semiquantitative reverse-transcriptase–polymerase chain reaction. Concentration ranges of the compounds and dilutions for the samples were selected to cause morphological alterations in embryos after 96 h of exposure. Transcript levels of ESR1, pax6, and hsp70 were differentially altered at early developmental stages with patterns specific to the contaminant and the exposure time. However, further studies are needed to establish transcript levels of specific genes as biomarkers of sublethal effects in an environmental risk-assessment framework. Besides, studies including more generic responses, such as genes encoding antioxidant enzymes, together with genes related to embryonic development have to be developed to look for a battery of mechanistic endpoints for the evaluation of chemical exposure at the molecular level in a first-tier assessment. Environ Toxicol Chem 2013;32:2018–2025. © 2013 SETAC
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