VA opsin

Vertebrate ancient (VA) opsin and inner retinal photoreception in teleosts... 

Carp VAL-opsin Zebrafish VAL-opsin Salmon VA-opsin Smelt VAL-opsin... 

The opsins probably perform a variety of different tasks, but their known roles are as photosensors or photoisomerases (Foster Bellingham 2002). Photosensory opsins such as the rod and cone opsins, P opsin and VA opsin use light to activate a phototransduction cascade that ultimately results in a change in membrane potential of the photoreceptor cell. By contrast, photoisomerases are involved in photopigment regeneration. The best described photoisomerase is... 

Studies on teleost fish and mammals have demonstrated the existence of non-rod, non-cone ocular photoreceptors. In the case of VA opsin in the roach, electrophysiological evidence suggests that one function of this photosensory photopigment is to modulate the activity of retinal horizontal cells. To what end remains unclear, but this fits with the general role of horizontal cells in the teleost... 

TABLE 4 Summary of the major differences between vertebrate photosensory opsins (rod, cone, P and VA opsin), photoisomerases (RGR opsins), and members of the melanopsin family... 

Minamoto T, Shimizu I 2002 A novel isoform of vertebrate ancient opsin in a smelt fish, Plemglossus altivelis. Biochem Biophys Res Commun 290 280—286 Miyashita Y, Moriya T, Yamada K et al 2001 The photoreceptor molecules in Xenopus tadpole tail fin, in which melanophores exist. Zoolog Sci 18 671—674 Moriya T, Miyashita Y, Arai J, Kusunoki S, Abe M, Asami K 1996 Light-sensitive response in melanophores of Xenopus laevis I. Spectral characteristics of melanophore response in isolated tail fin of Xenopus tadpole. J Exp Zool 276 11-18 Moutsaki P, Bellingham J, Soni BG, David-Gray ZK, Foster RG 2000 Sequence, genomic structure, and tissue expression of carp (Cyprinus carpio L.) vertebrate ancient (VA) opsin. FEES Lett 473 316-322... 

Philp AR, Garcia-Fernandez J-M, SonlBG, Lucas RJ, Bellingham J, Foster RG 2000 Vertebrate ancient (VA) opsin and extraretinal photoreception in the atlantic salmon iSalmo salar). J Exp Biol 203 1925-1936... 

A key feature of both vertebrate and invertebrate opsin molecules is their ability to interact with a G protein, typically transducin, to initiate phototransduction (Ebrey Koutalos 2001). The third cytoplasmic loop that connects a-hehces V and VI contributes to the G protein binding and activation and is highly conserved amongst the rod and cone opsins (Fig. 1, Table 2). This conservation extends to the P opsin family. However, the third cytoplasmic loop of the VA... 

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