Expression of pineal ultraviolet- and green-like opsins in the pineal organ and retina of teleosts

In teleostean bony fishes, studies on the adults of various species have sh own that pineal photoreceptors are maximally sensitive to short- and middle -wavelength light, possibly utilising both rod-like and pineal-specific ops ins. Until recently, however, very little was known about the pineal opsins present in embryonic and larval teleosts and their relationships to opsins expressed by retinal photoreceptors. Our immunocytochemical studies have r evealed that, in Atlantic halibut, herring and cod, pineal photoreceptors e xpress principal phototransduction molecules during embryonic life before t hey appear in retinal photoreceptors. In cDNA from embryonic and adult hali but, we identified two partial opsin gene sequences, HPO1 and HPO4, with hi ghest homology to teleost green and ultraviolet cone opsins (72-83% and 71- 83% amino acid identity, respectively). In halibut, these opsins are expres sed in the pineal organ of embryos and appear in the retina of larvae. Our recent in situ hybridisation studies with RNA probes for HPO1 and HPO4 demo nstrate the presence of green-like opsin mRNAs in the pineal organ and the retina of herring, cod, turbot, haddock, Atlantic salmon, zebrafish and thr ee species of cichlid, and of ultraviolet opsins in the retinas of zebrafis h, Atlantic salmon, turbot and the three cichlid species. We conclude that the halibut pineal organ appears to have the potential for both ultraviolet and green photosensitivity from the embryonic stage and that the retina ma y acquire the same potential during the larval stages. In the other teleost s studied, although both pineal and retinal photoreceptors seem to utilise a green-like opsin from the larval stage, ultraviolet photoreception appear s to be restricted to the retina.