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Paul FitzGerald, Roy Quinlan; Filensin and CP49 expression are not restricted to lens fiber cells. Invest. Ophthalmol. Vis. Sci. 2013;54(15):5736.
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© ARVO (1962-2015); The Authors (2016-present)
Filensin and CP49 are members of the Intermediate Filament family of proteins, but are possibly the most divergent members yet identified. Both were discovered in the lens fiber cell, and have long been considered strong fiber cell-specific markers. Data from different sources, however, have raised the possibility that expression of these two proteins may not be restricted to the fiber cell.
Several different antibody preparations to each protein were used to compare CP49 and filensin immunoreactivity in "wild type" and CP49/filensin knockout mouse strains.
Both CP49 and filensin are expressed in the lens epithelium of older, "wild type" mice, but not in younger mice. Immunoreactivity localizes to a relatively large, punctate structure, commonly found adjacent to the cell's nucleus. Immunoreactivity drops off near the bow region, and is absent from cells that have begun the elongation process. No reactivity was seen in the lenses of congenic CP49 and filensin knockout mice.
To our knowledge this is the first demonstration of CP49 and filensin immunoreactivity in cells other than lens fiber cells. The labeling pattern is not suggestive of a role as filamentous cytoskeleton, but rather resembles localization to a specific organelle. However, immunolabeling at the electron microscope level has not yet succeeded in identifying the target of labeling. It is intriguing that epithelial cells of younger animals are devoid of labeling, suggesting a maturation-dependent shift in the functional demands of lens epithelial cells. However, while several functons of these proteins have been determined for fiber cells, the function of these proteins in lens epithelium is currently unknown. These data suggest that CP49 and filensin may contribute additional functionality to the biology of the lens, and that their immunoreactivity has limitations as markers of fiber cell differentiation
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