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Robert S. Fischer, Andria Lee, Velia M. Fowler; Tropomodulin and Tropomyosin Mediate Lens Cell Actin Cytoskeleton Reorganization In Vitro. Invest. Ophthalmol. Vis. Sci. 2000;41(1):166-174.
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purpose. To determine the role of the actin cytoskeleton regulatory proteins
tropomyosin and tropomodulin (Tmod) in the reorganization of the actin
cytoskeleton during lens epithelial cell differentiation.
methods. Primary cultures of chick lens epithelial cells were allowed to
differentiate in vitro to form lentoid bodies. Localization of F-actin,
Tmod, and tropomyosin were determined by immunofluorescent staining
followed by confocal microscopy. Tropomyosin and Tmod isoform
expression was determined by immunoprecipitation and western blot
results. In undifferentiated epithelial cells F-actin was organized in polygonal
arrays of stress fibers and was also associated with the adherens belt.
In contrast, F-actin in differentiated cells was predominantly
associated with membranes in a reticular or fibrillar pattern and was
organized in curvilinear fibrils in the cytoplasm. Tmod was not
detected in the undifferentiated epithelial cells but was expressed
upon cell differentiation and assembled into F-actin and non–F-actin
structures. Tmod isoforms expressed in the lens cell cultures were
identical with those expressed in the embryonic chick lens fiber cells.
Tropomyosin was associated with the polygonal arrays of stress fibers
in the undifferentiated epithelial cells and was recruited to cortical
F-actin at the cell periphery during differentiation. This occurred
coincident with a shift in tropomyosin isoform expression.
conclusions. Expression and sequential assembly of low-molecular-weight tropomyosin
and Tmod into the cortical actin cytoskeleton of differentiated lens
cells may help to reorganize the actin cytoskeleton during
morphogenetic differentiation. Moreover, lens epithelial cell
differentiation may include the generation of novel Tmod-containing,
non–F-actin cytoskeletal structures.
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