Phototransduction cascade and circadian oscillator in chicken pineal gland

Toshiyuki Okano, Yoshitaka Fukada

Research output: Contribution to journalShort survey

29 Citations (Scopus)

Abstract

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 α-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.

Original languageEnglish
Pages (from-to)145-151
Number of pages7
JournalJournal of Pineal Research
Volume22
Issue number3
DOIs
Publication statusPublished - 1997 Apr
Externally publishedYes

Keywords

  • Chicken
  • Circadian clock
  • Iodopsin
  • Photoreceptor
  • Phototransduction cascade
  • Pinopsin
  • Rhodopsin

ASJC Scopus subject areas

  • Endocrinology

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