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S.G. Dann, W.T. Allison, C.W. Hawryshyn; Examination of Ontogenetic Changes in Vision in Pacific Salmon Using Retinal Opsin Genomics . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4539.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Pacific salmon (Oncorhynchus spp.), undergo considerable morphometric and physiological changes during their life history. As anadromous (migratory) fish, salmon must adapt their physiology from that suitable for a freshwater environment to saltwater environment during oceanic migration and back to freshwater during spawning. One of the well-documented ontogenetic changes in the retina of salmon is the loss of UV photosensitivity and the subsequent remodeling of the retina via loss of the SWS1 cone through apoptosis. The period leading up to the return migration to freshwater for spawning is marked by the regeneration of SWS1 cones and hence a reacquisition of UV sensitivity. Life history events around the period of spawning result in multiple morphometric changes including a dramatic shift in skin color from olive green to red through deposition of carotenoids in the skin. The goal of this research was to consider the physiological and morphological changes in the retina and the visual environment of salmon using a genomics approach Methods: RACE PCR was used to acquire full legnth sequence data of five retinal opsin gene types from rainbow trout. Subsequent evolutionary RT-PCR was employed to acqire the retinal opsin gene sequences from Pacific salmon and the Atlantic salmon (Salmo salar). Z-tests of positive selection were used on the acquired opsin gene open reading frames. Genome walking and chromatin immunoprecipitation were used to analyze transcription factor binding sites on opsin gene proximal promoters of rainbow trout. Results: Full length SWS2, SWS1, LWS, RH1, and RH2 gene sequences were acquired from six Pacific salmon species and the Atlantic salmon. Positive selection was detected statistically in the LWS opsin gene. NF-ΚB and c-jun were shown to bind exclusively to the SWS1 gene promoter in the rainbow trout retina. Conclusions: The LWS gene of the Pacific salmon is undergoing adaptive evolution likely related to the sexually selected dimorphism described above. Furthermore, the specific amino acid changes that occur in opsins between the species examined will allow a direct biochemical explanation of differing microspectrophotometric λmax values acquired for each opsin from each species. NF-ΚB and c-jun have been previously implicated in photoreceptor specific apoptosis and are shown here to be directly linked to SWS1 opsin expression in vivo. This research was supported by equipment and operating grants from the Natural Sciences and Engineering Research Council (CWH), a National Sciences and Engineering Research Council PGS-B (SGD) and an Alzheimer's Foundation of BC/Canada Fellowship (WEA)
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