Nature Biotechnology
17, 165 - 169 (1999)
doi:10.1038/6165
Conditional expression and signaling of a specifically designed G
i-coupled receptor in transgenic miceCharles H. Redfern1, 2, Peter Coward1, Michael Y. Degtyarev1, Elena K. Lee1, Andrew T. Kwa1, Lothar Hennighausen3, Hermann Bujard4, Glenn I. Fishman5
& Bruce R. Conklin1, 21
Gladstone Institute of Cardiovascular Disease, Gladstone
Institute of Neurological Disease, University of California, San
Francisco, CA 94141. 2
Department of Medicine, University of California,
San Francisco, CA 94141. 3
National Institute of Diabetes, Digestive and Kidney
Diseases, National Institutes of Health, Bethesda, MD
20982. 4
Zentrum für Moleculare Biologie der Universitat
Heidelberg, Heidelberg, Germany. 5
Mt. Sinai School of Medicine, New York,
NY 10029.
Correspondence should be addressed to Bruce R. Conklin (bconklin@gladstone.ucsf.edu; website:
http://gladstone.ucsf.edu/conklin.html).G protein signalingengineered opioid receptorsynthetic ligandTo control G protein signaling in vivo, we have modified G protein−coupled
receptors to respond exclusively to synthetic small molecule agonists and
not to their natural agonist(s). These engineered receptors are designated
RASSLs (receptor activated solely by a synthetic ligand). A prototype RASSL
(Ro1) based on the Gi−coupled  opioid receptor was
expressed in transgenic mice under the control of the tetracycline transactivator
(tet) system. Activation of Ro1 expressed in the heart decreased heart rate
by up to 80%, an expected effect of increased Gi signaling. Maximal
heart rate changes 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 on heart rate and the desensitization occurred, even though
Ro1 is derived from 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 Gi signaling is known
to control physiologic events 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.
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