Conditional expression and signaling of a specifically designed G(i)-coupled receptor in transgenic mice

To control G protein signaling in vivo, we have modified G protein-coupled receptors to respond exclusively to synthetic small molecule agonists and n ot to their natural agonist(s), These engineered receptors are designated R ASSLs (receptor activated solely by a synthetic ligand), A prototype RASSL (Ro1) based on the G(j)-coupled kappa opioid receptor was expressed in tran sgenic mice under the control of the tetracycline transactivator (tet) syst em, Activation of Ro1 expressed in the heart decreased heart rate by up to 80%, an expected effect of increased G(j) signaling. Maximal heart rate cha nges occurred in less than 1 min, demonstrating the speed of this inducible signaling system. This Ro1-mediated slowing of heart rate was also subject to desensitization, which lasted more than 24 h. Both the initial effect o n heart rate and the desensitization occurred, even though Ro1 is derived f rom a human opioid receptor not normally involved in heart rate control. In addition, the tet system was used to induce Ro1 expression in hepatocytes and salivary gland, where G(j) signaling is known to control physiologic ev ents such as proliferation and secretion, These studies demonstrate that a RASSL can be inducibly expressed in several mouse tissues and used in vivo to activate G protein signaling in a controllable fashion.