Milena Frelih

• Many environmental chemicals have the potential to interfere with the inherent endocrine system of both humans as well as organisms in the environment, and are therefore called endocrine disrupting chemicals (EDCs). EDCs can induce long-lasting adverse effects in development, reproduction, behavior, and immunity. The current approach for screening substances for EDCs involves the use of juvenile or adult fish for in vivo testing, which is resource-intensive and time-consuming. The utilization of zebrafish embryos in ecotoxicological testing has previously been explored with the aim of reducing the need for in vivo animal testing. To this end, a combined transcriptomics and proteomics approach was applied to identify toxicogenomic signatures associated with the disruption of estrogen hormone signaling in zebrafish (Danio rerio) embryos. In this study, zebrafish embryos were exposed to different sublethal concentrations of 17β-estradiol, bisphenol A and fulvestrant as model substances to identify amplified and suppressed estrogen hormone signaling in a modified zebrafish embryo toxicity test (zFET) (OECD 236). Both total RNA and proteins were extracted from the different treatments and the non-treated controls. While no significant effects on survival or hatching rate were detected in the treated groups in comparison to the control groups, these studies successfully identified genes associated with estrogen-dependent modes of action, such as cyp19a1b and nr4a1 which exhibited significant regulation upon exposure to 17β-estradiol, bisphenol A or fulvestrant. This study provides evidence that zebrafish embryos are a suitable vertebrate model for identifying potential hazards associated with chemicals that affect estrogen synthesis and for investigating the potential endocrine disrupting effects of compounds. This approach provides additional evidence for the identification of potential endocrine disruptors (EDs) and has the potential to significantly reduce the reliance on animal testing in higher tier studies.