Endocrine Abstracts

Due to its rapid development and high fecundity, the zebrafish is a standard model in developmental biology and genetics. Furthermore, key hormone systems present in mammals are already active in zebrafish larvae. The endocrine system and the circadian clock are closely linked, and also the circadian system of zebrafish matures early in development. The small size of zebrafish larvae makes them particularly suitable for chemical screens in vivo: Larvae can be kept for days in 96 well plates and be exposed to different chemicals under varying environmental conditions. To harness these in vivo chemical screening possibilities of zebrafish larvae for chronobiology and endocrinology, we have generated transgenic zebrafish lines based on simple enhancer elements for the monitoring of circadian clock function and glucocorticoid signaling. Thus, a zebrafish line carrying a luciferase reporter construct regulated by 4 circadian E-box elements indicates core clock feedback loop activity early during development, and allows the detection of compound effects on period length over a broad range (1–12 h) in vivo under conditions suitable for high-throughput screening. Another luciferase reporter line carrying four glucocorticoid response elements (GREs) detects stress induced cortisol release in single larvae and can monitor the maturation of the stress response during development. This assay can also detect effects of environmental pollutants on endocrine signaling that are not detectable with cell culture assays: we observed a disruption of glucocorticoid signaling with environmentally relevant concentrations of an organotin compound that requires metabolization within the organism. A pilot screen with an FDA approved drug library of 640 compounds detected bona fide glucocorticoids present in the library with high specificity, as well as one additional compound stimulating cortisol production in vivo. Our lines provide versatile tools for chronobiology, stress research, environmental monitoring of endocrine disruptors and pharmaceutical screens targeting glucocorticoid signaling and circadian clock function.

Declaration of funding

This work was supported by the Deutsche Forschungsgemeinschaft (DFG, grant number DI913/4-1), by the Studienstiftung des deutschen Volkes (to M Weger), the European Commission’s 7th Framework Programme (ZF-HEALTH project, EC Grant Agreement HEALTH-F4-2010-242048), and the BioInterfaces (BIF) Programme of the Karlsruhe Institute of Technology (KIT) in the Helmholtz Association.