Phototransduction cascade and circadian oscillator in chicken pineal gland.
The chicken pineal gland has an endogenous circadian oscillator that controls the diurnal oscillation of N-acetyltransferase activity responsible for melatonin rhythm. It has been speculated that the chicken pineal cell contains a photoreceptive molecule that receives the environmental light signal and transmits the signal to the oscillator for resetting the phase. In spite of several lines of evidence suggesting the similarity between retinal and pineal photon-signal transducing proteins, the identity of the photoreceptive molecule had been an open question. In 1994, we isolated a pineal cDNA encoding a novel photoreceptive molecule and named it "pinopsin." The protein expressed in 293EBNA cells bound 11-cis-retinal to form a blue-sensitive pigment with an absorption maximum at about 470 nm. A putative G-protein interaction site of pinopsin shared a relatively high similarity in amino acid sequence to that of rhodopsin, implying that pinopsin functionally couples with transducin or transducin-like G-protein(s) in the pineal cells. We have cloned a cDNA for chicken pineal transducin alpha-subunit, and the deduced amino acid sequence contained a potential site to be ADP-ribosylated by pertussis toxin (PTX). Therefore, the transducin-mediated pathway could be blocked by PTX, though previous studies showed that treatment of the cultured chicken pineal cells with PTX had no effect on the light-induced phase-shift of the oscillator. Accordingly, it is unlikely that transducin mediates the light-input pathway to the oscillator, which may involve PTX-insensitive G-protein(s) or some unidentified component(s). The G-protein coupled receptor-mediated signaling processes regulating melatonin synthesis are discussed.
Okano
T
T
Department of Biophysics and Biochemistry, Graduate School of Science, University of Tokyo, Japan.
Fukada
Y
Y
D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D030161:Avian Proteins; D001665:Binding Sites / Q000235:genetics; D002940:Circadian Rhythm / Q000502:physiology* / Q000528:radiation effects*; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D019204:GTP-Binding Proteins / Q000378:metabolism; D008954:Models, Biological; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D037342:Pertussis Toxin; D010786:Photoreceptor Cells / Q000737:chemistry / Q000502:physiology; D010870:Pineal Gland / Q000502:physiology* / Q000528:radiation effects*; D017299:Rod Opsins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D015293:Transducin / Q000378:metabolism; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D000246:Adenosine Diphosphate Ribose; D030161:Avian Proteins; D018076:DNA, Complementary; D019204:GTP-Binding Proteins; D009419:Nerve Tissue Proteins; D037342:Pertussis Toxin; D017299:Rod Opsins; D015293:Transducin; D010566:Virulence Factors, Bordetella; C090139:OPNP protein, chicken