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J. Yang, X. Liu, Y. Zhao, M. Adamian, B. Pawlyk, T. Li; Subcellular Localization of Whirlin and Its Interaction With Ush2a in the Photoreceptors . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2848.
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Whirlin is a protein with three PDZ domains and a proline–rich region. It is expressed at the tips of stereocilia in hair cells and interacts with myosin XVa. Genetic studies indicate that it is essential for stereocilia elongation and may participate in the coordinated actin polymerization and membrane growth of stereocilia. Since we have found that whirlin also exists in the retina, the goal of this study was to investigate its expression, localization and potential function in the retina.
Whirlin antibodies and whirlin knockout mice were generated. The expression and localization of whirlin in the retina were determined by Western blotting, immunofluoresence and immunoelectron microscopy with whirlin–deficient mice as negative controls. The function of whirlin in the retina was analyzed by evaluating whirlin–deficient mice using light microscopy, electroretinography (ERG), and a series of biochemical assays.
Whirlin is expressed as the long isoform but not the short isoform in the retina. It is located at the apex of the inner segments of photoreceptors, corresponding to a structure known as the periciliary ridge complex in frog. It was found to interact with Ush2A through its first two PDZ domains and the C–terminal PDZ–binding domain of Ush2A. The interaction between whirlin and Ush2A is essential for their correct localization in the photoreceptors, as either protein mislocalizes in the absence of its interacting partner. Young whirlin–deficient mice have normal ERGs, suggesting that whirlin does not participate directly in photoreceptor signal transmission in the retina.
Whirlin is required for the correct subcellular localization of the Ush2A protein in the photoreceptors. Given this role, it is predicted that the genetic defects of whirlin may lead to an Usher type condition in the retina as well as to its known involvement in congenital deafness.
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