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Stephan C. Neuhauss, Jingjing Zang, Edda Kastenhuber, Matthias Gesemann; The Role of Recoverin in Zebrafish Cone Vision. Invest. Ophthalmol. Vis. Sci. 2012;53(14):761.
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Recoverin, a neuronal specific Ca2+-binding protein, has been found in vertebrate photoreceptors and its function is well studied in rods. It has been proposed that in darkness, when cytoplasmic Ca2+ concentration is high, Recoverin inhibits rhodopsin kinase. During the light response, there is a dynamic fall in intracellular Ca2+ concentration resulting in a redistribution of Recoverin, speeding rhodopsin phosphorylation. Recently, it has been directly demonstrated in intact rods, that photoexcited rhodopsin lifetime is modulated by background light and this modulation may require Recoverin. However, the mechanism underlying visual pigment quenching is not well established in cones. It has been reported that zebrafish cone visual pigment phosphorylation is Ca2+ sensitive and deficiency of cone specific kinase produces prolonged cone response recovery, suggesting that recoverin may play a similar role in regulating visual pigment inactivation in cones as in rods. In this study, we therefore use the zebrafish cone-dominate retina to investigate the function of Recoverin in vision.
Phylogenetic analysis has been used to identify members of the zebrafish Recoverin family. In situ hybridization was performed on 5 days post fertilization zebrafish larvae and adult sections to investigate the expression pattern of each zebrafish recoverin (rcv) gene.
We identified four individual members of the recoverin gene family. For the direct mammalian ortholog rcv1, we found two paralogs (rcv1a and rcv1b) in the zebrafish genome. Similarly we found two paralogs for recoverin2 (rcv2a and rcv2b). All four genes are expressed in the photoreceptor cell layer and pineal gland at 5 days post fertilization. Expression studies in the adult eye reveals expression in specific subtype of photoreceptors with additional expression of rcv1b in the retinal ganglion cell layer. rcv2a and rcv2b are both expressed in blue-sensitive cones and double cones, while rcv1a is found to be expressed in UV-sensitive cones and rods.
The zebrafish genome harbors four recoverin orthologs that are all expressed in a subset of photoreceptors. The cloning of these gene will enable us to down regulate these genes and study their contribution to vision by electrophysiological means.
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