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V. L. Bonilha, K. C. Shadrach, M. E. Rayborn, Y. Li, J. Wu, N. S. Peachey, I. Saotome, A. I. McClatchey, J. G. Hollyfield; Analysis of Retinal Pigment Epithelium (RPE) and Retina in an RPE-Ezrin Knockout Model. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3033.
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In the eye, ezrin (an actin-binding protein) has been localized to apical microvilli of Müller cells and RPE apical microvilli and basal infoldings. We have previously shown that ezrin is expressed and plays an important role in establishing and maintaining apical microvilli of RPE and Müller cells, and RPE basal infoldings. In ezrin-/- mice, we also noted that photoreceptor development was delayed as compared to their development in wild type littermates. To dissect the effects of ezrin absence in the RPE, we generated RPE-specific ezrin knockout mouse model.
The RPE-ezrin-/- mice were generated by breeding of ezrin flox/flox mice with a transgenic line carrying a RPE-specific promoter driving the expression of cre recombinase. Eyecups were fixed and analyzed by transmission electron microscopy (TEM). Also, cryosections of RPE-ezrin-/- mice and control littermates were processed for immunofluorescence with antibodies specific to RPE and photoreceptors.
TEM analysis indicates that while the RPE microvilli and basal infoldings are formed, they appear abnormal ultrastructurally. The membranes of apical microvilli and cytoplasm were very electrondense, as were the membranes of the basal infoldings membranes. These observations suggest an alteration in the lipid to protein ratio. Phalloidin staining of RPE-ezrin-/- microvilli revealed no difference when compared to the control littermates. However, RPE-ezrin-/- expressed low levels of microvilli transporters such as the glucose transporter Glut-1. All of the major components of the dc-ERG were present in RPE-ezrin-/- mice.
RPE-ezrin-/- mice demonstrate that ezrin is required for the formation and maintenance of the RPE polarized phenotype and that ezrin plays a crucial role in the morphogenesis of both apical microvilli and basal infoldings.
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