In Vivo and In Vitro Reporter Systems for Studying Nuclear Receptor and Ligand Activities

Publisher Summary This chapter focuses on the in vivo and in vitro reporter systems for studying nuclear receptor and ligand activities. Nuclear receptor (NR) ligands are generally small and lipophilic molecules making NRs highly attractive drug targets. These same properties render ligands challenging to the researchers interested in NR biology. Novel ligands for orphan NRs are not easily identified by biochemical methods and often cannot be identified by expression cloning or related strategies. The chapter describes alternative strategies that are based on transgenic mouse technology allowing NR activities to be assayed in vivo . It provides examples of complementary in vitro assays that are useful in verifying and extending results obtained in transgenic mouse experiments. It is well established that several nuclear receptors are activated by ligand independent mechanisms, which in transgenic experiments could lead to reporter induction in the absence of ligand. NR ligands may be unstable and/or sensitive to light. Therefore, all preparations should be kept on ice, and care should be taken to avoid unnecessary exposure to light. Further improvements in established methods, as well as the development of techniques to search for natural NR ligands in vivo , will be an essential complement to the screening efforts currently in progress, in particular within pharmaceutical and biotech companies. Although synthetic ligands are invaluable as tools, the identification of natural ligands will undoubtedly prove vital for achieving a complete understanding of the roles played by NRs in vivo .