title: Rod-type transducin alpha-subunit mediates a phototransduction pathway in the chicken pineal gland.
abstract: The chicken pineal gland is a photosensitive neuroendocrine organ producing melatonin in circadian clock-regulated and light-sensitive manners. To understand the relationship between the photoreceptive molecule pinopsin and the light-dependent melatonin suppression that is sensitive to pertussis toxin treatment, we have searched for pertussis toxin-sensitive G protein alpha-subunits expressed in the chicken pineal gland. Here we report the cDNA cloning of the pineal transducin alpha-subunit (Gtalpha), which is highly homologous to human retinal rod cell-specific Gt(1)alpha. Concurrent cDNA cloning of chicken retinal Gt(1)alpha and Gt(2)alpha (rod and cone cell-specific alpha-subunits of transducin, respectively) revealed that the chicken pineal Gtalpha is identical to the retinal Gt(1)alpha. Double-immunostaining analysis of the chicken pineal sections localized Gt(1)alpha-immunoreactivity in the rudimentary outer segments of both follicular and parafollicular pinealocytes that were immunopositive to anti-pinopsin antibody. To examine whether pineal Gt(1)alpha is involved in the pineal phototransduction pathway, trypsin protection assay was applied for detecting the conversion of GDP-bound Gt(1)alpha into the guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS)-bound form in the pineal membrane homogenate. It was clearly demonstrated that the pineal Gt(1)alpha is activated in a light-dependent manner in the presence of GTPgammaS. These data together suggest strongly that pineal Gt(1)alpha mediates the phototransduction pathway triggered by pinopsin in the chicken pinealocytes.
authors.affiliation: Department of Biophysics and Biochemistry, Graduate School of Science, The University of Tokyo, Tokyo, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Kasahara
authors.forename: T
authors.initials: T
authors.lastname: Okano
authors.forename: T
authors.initials: T
authors.lastname: Yoshikawa
authors.forename: K
authors.initials: K
authors.lastname: Yamazaki
authors.forename: Y
authors.initials: Y
authors.lastname: Fukada
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D030161:Avian Proteins; D002645:Chickens; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006153:Guanosine Diphosphate / Q000378:metabolism; D008027:Light; D055537:Light Signal Transduction; D008297:Male; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000032:analysis / Q000502:physiology; D010870:Pineal Gland / Q000737:chemistry / Q000502:physiology*; D017299:Rod Opsins / Q000032:analysis / Q000502:physiology; D017385:Sequence Homology; D015293:Transducin / Q000032:analysis / Q000737:chemistry / Q000502:physiology*
chemical_list: D030161:Avian Proteins; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006153:Guanosine Diphosphate; D009419:Nerve Tissue Proteins; D017299:Rod Opsins; D015293:Transducin; C090139:OPNP protein, chicken