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W.-K. Lo, S. K. Biswas, M. H. Elliott; Role of Aquaporin-0 in Lens Membrane Architecture - Ultrastructural Perspective From Intact Lenses of Caveolin1-Null and Emory Mutant Mice. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3873.
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© ARVO (1962-2015); The Authors (2016-present)
AQP0 has been suggested to play multiple functions in lens fiber cells. It may serve as (1) water channels in major cortical fibers, (2) a regulatory protein for gap junction function, and (3) aquaporin junctions for adhesion between mature fiber cells. In our early studies, we have revealed that AQP0 proteins, in the form of square arrays, are not registered into symmetrical cell-cell junctions in the intact lens. Rather, they are arranged into a unique asymmetrical configuration associated with the formation of undulating ridge membrane surfaces. Here we use Cav1-null and Emory mutant mouse models to examine whether AQP0 is assembled into the characteristic square array junctions during extensive formation of membrane ridges in the intact lenses.
SEM, high pressure freezing, freeze-fracture TEM, and freeze-fracture immunogold labeling were used in this study.
SEM showed that in the normal lens at postnatal day 14 (P14), the membrane interdigitations in the form of tongue-and-grooves or ridges were distributed abundantly from inner cortical fibers toward the lens core, beginning at ~600um deep from the equatorial capsule surface. These ridges were later extended toward a more superficial cortical region at ~400um from the surface at P30, suggesting that these ridges undergo expansion during normal lens growth. Surprisingly, in the Cav1-null mice at P30, we regularly observed widespread formation of ridges from the outer cortex toward the nucleus, beginning at ~200um deep from the equatorial surface. The newly-formed ridges with elaborate bundles almost covered the entire fiber membrane surface. Similar distributions of extensive newly-formed ridges were also observed in the Emory mouse lenses. By high pressure freezing and freeze-fracture TEM, we consistently observed that the distinctive arrangement of square arrays (AQP0) was indeed specifically distributed along the single undulating surface of newly-formed ridge membranes in the cortical fibers. Freeze-fracture immunogold labeling confirmed that the AQP0 antibody was localized asymmetrically along the ridge membrane surfaces.
The extensive formation of ridge membranes in Cav1-null and Emory mutant mice provides us with excellent animal models to critically examine the role of AQP0 in the lens membrane architecture. Our results suggest that AQP0 square arrays play an important role in the development of ridge membrane interdigitations found in both normal and mutant mouse lenses.
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