Ligand-Mediated Receptor Assembly as an End Point for High-Throughput Chemical Toxicity Screening

The high throughput screening of chemicals for interaction with intracellular targets is gaining prominence in the toxicity evaluation of environmental chemicals. We describe ligand-mediated receptor assembly as an early event in receptor signaling and its application to the screening of chemicals for interaction with targeted receptors. We utilized bioluminescence resonance energy transfer (BRET) to detect and quantify assembly of the methyl farnesoate receptor (MfR) in response to various high-production volume and other chemicals. The hormone methyl farnesoate binds to the MfR to regulate various aspects of reproduction and development in crustaceans. The MfR protein subunits Met and SRC, cloned from Daphnia pulex, were fused to the fluorophore, mAmetrine and the photon generator, Rluc2, respectively. Ligand-mediated receptor assembly was measured by photon transfer from the photon donor to the fluorophore resulting in fluorescence emission. Overall, the BRET assay had comparable or greater sensitivity as compared to a traditional reporter gene assay. Further, chemicals that screened positive in the BRET assay also stimulated phenotypic outcomes in daphnids that result from MfR signaling. We concluded the BRET assay is an accurate, sensitive, and cost/time efficient alternative to traditional screening assays.