Exo-rhodopsin: a novel rhodopsin expressed in the zebrafish pineal gland.
The zebrafish, a useful animal model for genetic studies, has a photosensitive pineal gland, which has an endogenous circadian pacemaker entrained to environmental light-dark cycles [G.M. Cahill, Brain Res. 708 (1996) 177-181]. Although pinopsin has been found in the pineal glands of birds and reptiles, the molecular identity responsible for fish pineal photosensitivity remains unclear. This study reports identification of a novel opsin gene expressed in the zebrafish pineal gland. The deduced amino acid sequence is similar to, but not identical (74% identity) with that of canonical rhodopsin in the zebrafish retina. This novel rhodopsin is expressed in the majority of pineal cells but not in retinal cells, and hence named exo-rhodopsin after extra-ocular rhodopsin. This study first shows that two different rhodopsin genes are expressed in an individual animal each within a unique location. A phylogenetic analysis indicated that the exo-rhodopsin gene was produced by a duplication of the rhodopsin gene at an early stage in the ray-finned fish lineage. As expected, the exo-rhodopsin gene was found in the medakafish and European eel genomes, suggesting strongly that exo-rhodopsin is a pineal opsin common to teleosts. Identification of exo-rhodopsin in the zebrafish provides an opportunity for studying the role of pineal photoreceptive molecules by using genetic approaches.
Mano
H
H
Department of Biophysics and Biochemistry, Graduate School of Science, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo, Japan.
Kojima
D
D
Fukada
Y
Y
D000595:Amino Acid Sequence; D000818:Animals; D001921:Brain / Q000378:metabolism; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics; D015870:Gene Expression; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D008969:Molecular Sequence Data; D010802:Phylogeny; D010870:Pineal Gland / Q000737:chemistry / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012160:Retina / Q000378:metabolism; D012243:Rhodopsin / Q000032:analysis / Q000235:genetics*; D017299:Rod Opsins / Q000235:genetics; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D014018:Tissue Distribution; D015027:Zebrafish / Q000235:genetics*
D018076:DNA, Complementary; D012333:RNA, Messenger; D017299:Rod Opsins; C403706:exorhodopsin; D012243:Rhodopsin