The Journal of Neuroscience, September 1, 2002, 22(17):7321-7325
BRIEF COMMUNICATION
Opsin-G11-Mediated Signaling Pathway for Photic
Entrainment of the Chicken Pineal Circadian Clock
Takaoki
Kasahara1, 3,
Toshiyuki
Okano1, 3,
Tatsuya
Haga2, 3, and
Yoshitaka
Fukada1, 3
1 Department of Biophysics and Biochemistry, Graduate
School of Science, 2 Department of Neurochemistry, Faculty
of Medicine, The University of Tokyo, Tokyo 113-0033, Japan, and
3 Core Research for Evolutional Science and
Technology of Japan Science and Technology Corporation, Tokyo
105-0011, Japan
Light is a major environmental signal for entrainment of the
circadian clock, but little is known about the intracellular phototransduction pathway triggered by light activation of the photoreceptive molecule(s) responsible for the phase shift of the clock
in vertebrates. The chicken pineal gland and retina contain the
autonomous circadian oscillators together with the photic entrainment
pathway, and hence they represent useful experimental models for the
clock system. Here we show the expression of G11
, an subunit of heterotrimeric G-protein, in both tissues by cDNA cloning,
Northern blot, and Western blot analyses. G11
immunoreactivity was colocalized with pinopsin in the chicken pineal
cells and also with rhodopsin in the outer segments of retinal
photoreceptor cells, suggesting functional coupling of
G11 with opsins in the clock-containing photosensitive
tissues. The physical interaction was examined by coimmunoprecipitation
experiments, the results of which provided evidence for light- and
GTP-dependent coupling between rhodopsin and G11. To
examine whether activation of endogenous G11 leads to a
phase shift of the oscillator, Gq/11-coupled m1-type muscarinic acetylcholine receptor (mAChR) was ectopically expressed in
the cultured pineal cells. Subsequent treatment of the cells with
carbamylcholine (CCh), an agonist of mAChR, induced phase-dependent phase shifts of the melatonin rhythm in a manner very similar to the
effect of light. In contrast, CCh treatment induced no measurable
effect on the rhythm of nontransfected (control) cells or cells
expressing Gi/o-coupled m2-type mAChR, indicating
selectivity of the G-protein activation. Together, our results
demonstrate the existence of a G11-mediated opsin-signaling
pathway contributing to the photic entrainment of the circadian clock.
Key words:
G11; phototransduction; circadian
rhythm; pinopsin; pineal gland; retina
Copyright © 2002 Society for Neuroscience 0270-6474/02/22177321-05$05.00/0
