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G.A. Zampighi, N. Fain, L.M. Zampighi, J. Hortwitz; The Structure of the Lens Fiber Cytoskeleton Determined by Conical Electron Tomography . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1973.
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© ARVO (1962-2015); The Authors (2016-present)
Despite a wealth of information gathered with biochemical and molecular biology methods, the three–dimensional structure of the lens fiber cell cytoskeleton remains poorly understood. A reason for this dearth of information has been the low resolution of the methods used to image the cytoskeleton in the fiber environment. Here, we used conical tomography in an effort to resolve the structure of the fiber cytoskeleton in three dimensions and at higher resolution.
We used conical tomography to image the cytoskeleton of rat lenses prepared by thin sectioning and freeze–fracture electron microscopy. The specimens were imaged tilted at a fixed angle of 55 degrees, and then rotated at 5 degrees increments until completing a 360 degrees turn. The conical series were then aligned to a common reference system and later reconstructed using the weighted back projection algorithm. The resulting 3D maps exhibited ∼4 nm resolution.
The cytoskeleton is comprised of a meshwork of thin filaments extending throughout the cytoplasm of the fiber cell. Each thin filament is decorated with globular units 7–8 nm in diameter, often forming what appeared as tetramers or circles ∼16 nm in diameter. Adjacent decorated filaments associate with each other to form thicker filaments that most likely correspond to the beaded filaments described in chemical and structural studies. The number of these larger filaments and the frequency of their association in any given area of the lens seem to be the essential factors contributing to the structure of the cytoskeleton. Areas in the fiber where these beaded filaments coalesce into densely packed aggregates comprise the regions of high electron–density normally seen in the cytoplasm with conventional thin sectioning.
From a structural vantage point, the lens fiber cytoskeleton is comprised of filaments as well as globular units that in their association produce structures of both increasing dimensions and complexity. Thus the amorphous structures, seen in thin sectioning electron microscopy, result from the association of distinct elements of a much less complex nature.
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