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M. Salvador-Silva, S. Ghosh, M. Coca-Prados; Gene and Protein Expression of Rhodopsin, Rhodopsin Kinase and Arrestin in the Bovine Iris: Possible Role in a Non-visual Phototransduction Signal . Invest. Ophthalmol. Vis. Sci. 2003;44(13):423.
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Purpose: Recent studies have shown that components of phototransduction are expressed within the mammalian ocular ciliary epithelium [Bertazolli-Filho R et al. B.B.R.C. (2001) 284:317-25]. Because of the embryological relationship of the iris-ciliary epithelium with the photosensory retina and retinal pigment epithelium we have explored whether the iris also expresses components of phototransduction. Methods: Northern blots containing poly A+ RNA from iris and retina were prepared from young calve eyes and hybridized sequentially with radiolabeled cDNA specific probes including rhodopsin, rhodopsin kinase and arrestin. Antibodies to rhodopsin (Ret-P1, PA1-729), rhodopsin kinase (MA1-720) and arrestin (SCT-128, PA1-731) were used to immunoprecipitate respective proteins from iris and retina or used to probe Western blots with soluble and microsomal fractions. Indirect immunofluorescence was carried out on semithin cryostat sections of bovine iris and stained with the above antibodies. Results: By Northern blot hybridization, rhodopsin, rhodopsin kinase and arrestin mRNAs were detected in the bovine iris. The relative sizes of these transcripts coincided with those detected in the bovine retina. Immunoprecipitates from whole iris protein extracted with Triton X-100 revealed an enrichment of rhodopsin (36-kDa), rhodopsin kinase (66-kDa) and visual arrestin (48-kDa) proteins in the iris. By indirect immunofluorescence the antibodies labeled cells throughout the iris. Conclusions: The present data provides evidence that the iris expresses key genes involved in phototransduction. These studies also provide preliminary cellular and molecular evidence that in the iris-ciliary epithelium rhodopsin may be involved in a phototransduction signal pathway distinct from the one present in rod and cone photoreceptor cells.
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