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Christiana L. Cheng, Kathlyn J. Gan, Iñigo Novales Flamarique; The Ultraviolet Opsin Is the First Opsin Expressed during Retinal Development of Salmonid Fishes. Invest. Ophthalmol. Vis. Sci. 2007;48(2):866-873. doi: 10.1167/iovs.06-0442.
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purpose. To determine the spatial and temporal progression of opsin appearance during retinal development of salmonid fishes (genus Oncorhynchus and Salmo).
methods. Reverse transcription–polymerase chain reaction (RT-PCR) and in situ hybridization with riboprobes against the five classes of opsins present in salmonids (UV, blue, green, red, and rhodopsin) were used to establish the sequence of opsin appearance and the localization of opsins to specific morphologic photoreceptor types.
results. Both detection methods revealed that UV opsin mRNA was expressed first and was followed closely by red opsin mRNA. In situ hybridization results indicated the following opsin sequence: UV, red, rhodopsin, green, and blue. The UV opsin riboprobe labeled single cones, whereas the red and green riboprobes labeled opposite members of double cones. The blue riboprobe started labeling single center cones ∼1 month after initial UV riboprobe labeling, confirming a switch in opsin expression of these cones from UV to blue. All probes first labeled a small patch of cells in the centrotemporal retina, and expression then expanded primarily toward the temporal and dorsal retina, with the exception of the blue opsin which expanded ventrally at first.
conclusions. The sequence of cone opsin appearance in salmonid fishes is similar to that in mammals, in which a violet-blue (SWS1) opsin is expressed first followed by a red (M/LWS) opsin. This sequence is different from that in zebrafish, goldfish, and chick, in which red and green opsins are expressed first. As in mammals, rhodopsin expression in salmonid fishes arises after the first cone opsin. The findings show similarity in the sequence of opsin expression between a group of lower vertebrates, the salmonid fishes, and mammals.
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