Exo-rhodopsin: a novel rhodopsin expressed in the zebrafish pineal gland

Brain Res Mol Brain Res. 1999 Nov 10;73(1-2):110-8. doi: 10.1016/s0169-328x(99)00242-9.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Brain / metabolism
  • Cloning, Molecular
  • DNA, Complementary / chemistry
  • DNA, Complementary / genetics
  • Gene Expression
  • Immunohistochemistry
  • In Situ Hybridization
  • Molecular Sequence Data
  • Phylogeny
  • Pineal Gland / chemistry
  • Pineal Gland / metabolism*
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • Retina / metabolism
  • Rhodopsin / analysis
  • Rhodopsin / genetics*
  • Rod Opsins / genetics
  • Sequence Alignment
  • Sequence Analysis, DNA
  • Sequence Homology, Amino Acid
  • Tissue Distribution
  • Zebrafish / genetics*


  • DNA, Complementary
  • RNA, Messenger
  • Rod Opsins
  • exorhodopsin
  • Rhodopsin

Associated data

  • GENBANK/AB025312