Localization and diurnal expression of melanopsin, vertebrate ancient opsin, and pituitary adenylate cyclase-activating peptide mRNA in a teleost retina.

JOURNAL OF BIOLOGICAL RHYTHMS, Vol. 22 No. 6, December 2007 558-561 DOI: 10.1177/0748730407308285 © 2007 Sage Publications Melanopsin (Opn4) contributes to the entrainment of circadian rhythms in mammals. In rats, retinal ganglion cells expressing Opn4 sense light and regulate circadian entrainment (Hattar et al., 2002) by relaying light information to the SCN via release of neuropeptides, including glutamate and pituitary adenylate cyclase-activating peptide (PACAP) (Hannibal, 2006). Opn4 mRNA has also been found in horizontal and/or ganglion cells in teleost fish, including zebrafish, roach, and Atlantic cod, but in these species its function is unknown. Vertebrate ancient opsin (VA opsin), first found in Atlantic salmon (Soni and Foster, 1997) and subsequently in zebrafish, carp, smelt, and roach, may also contribute to circadian entrainment in teleosts. In roach, one type of horizontal cell is intrinsically photosensitive and depolarizes maximally in response to light of wavelengths matching VA opsin sensitivity (Jenkins et al., 2003), suggesting that VA opsin can provide photic information to the brain. We cloned and sequenced Opn4, VA opsin, and PACAP from an African cichlid fish, Astatotilapia burtoni (Fig. 1). The A. burtoni Opn4 amino acid transmembrane region resembles that of zebrafish Opn4a (77.4% identity) more than zebrafish Opn4m1 (67.1%). The 391–amino acid A. burtoni VA opsin is homologous to the VA-L isoform found in smelt (Minamoto and Shimizu, 2002). A. Localization and Diurnal Expression of Melanopsin, Vertebrate Ancient Opsin, and Pituitary Adenylate Cyclase-Activating Peptide mRNA in a Teleost Retina