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A. Sene, Sr., P. Fort, R. Benard, V. Fradot, D. Yaffe, U. Nudel, J.-A. Sahel, A. Rendon; Kir4.1 and AQP4 Channels Localization and Clustering in Müller Glial Cells Requires Dystrophin-Dp71/DAPs Complex. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2951.
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In addition to the full-length dystrophin (Dp427), the activation of internal promoters of the DMD gene (Duchenne Muscular Dystrophy) leads to the production of several short products. Dp71 is the major product of the DMD gene outside of the skeletal muscle. The purpose of this study was the characterization of Dp71 /Dystrophin Associated Protein (DAPs) complex responsible for the localization and clustering of Potassium channel Kir4.1 and water channel AQP4 in mouse Müller Glial Cells (MGC).
Dystrophin Dp71, DAPs, Kir4.1 and AQP4 were localized by immunocytochemical techniques in freshly dissociated MGC from wild-type (wt) and knock-out mice invalidated for Dp71 (Ko-Dp71). The components of DAPs complex were identified by coimmunoprecipitation using a membranous fraction enriched in Dp71; the end feet of MGC. Furthermore the membrane association of Dp71, DAPs, Kir4.1 and AQP4 was studied by analyzing, in a total retinal extract, their triton X-100 solubility.
Observation of freshly dissociated MGC showed that Dp71, DAPs, Kir4.1 and AQP4 were mainly localized on the end feet of MGC from wt mice. In the absence of Dp71, DAPs, Kir4.1 and AQP4 were delocalized all along MGC with a dramatic reduction of AQP4 staining. We also found by coimmunoprecipitation techniques that Dp71 was associated to DAPs (ß-dystroglycan, α-dystrobrevin and syntrophins), Kir4.1 and AQP4. Using triton X-100 solubilization experiments, we showed that Dp71 and DAPs were recovered in a detergent resistant membrane (DRM) fraction and in a soluble fraction in wt mice. Concerning Kir4.1 and AQP4, these proteins were recovered respectively in the soluble and the DRM fraction. In Dp71 null mice, we observed that all DAPs were fully recovered in the soluble fraction; Kir4.1 remains in the soluble fraction and in agreement with the immunocytochemistry results; the expression of AQP4 is down regulated
Here we show that Dp71 is responsible for the clustering of DAPs, Kir4.1 and AQP4 in the MGC. Our results also suggest that the localization of DAPs, Kir4.1 and AQP4 in precise membrane domains is under control of Dp71.
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