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S. S. Kumari, K. Varadaraj, R. T. Mathias; Role of Aquaporins on Lens Transparency. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2810.
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© ARVO (1962-2015); The Authors (2016-present)
In the mammalian lens AQP0 is expressed in the lens fiber cells whereas AQP1 is expressed in lens anterior and equatorial epithelial cells. AQP1 expression is shut down and AQP0 is turned on during secondary fiber cell differentiation. Why the lens switches expression from AQP1 in the equatorial epithelial cells to AQP0 in the differentiating secondary fiber cells is not known. The aim of this investigation was to determine the functional significance of the temporal and cell-specific expression of the two aquaporins in the lens.
Standard RT-PCR, immunostaining, western blotting, confocal microscopy, membrane water permeability assay and lens transparency evaluation techniques were used to investigate the developmental expression of mouse lens aquaporins and lens transparency.
AQP0 transcript and protein were identified at E11.25 in the differentiating primary fiber cells; its synthesis continued through the adult stage in secondary fiber cells, which differentiate from equatorial epithelial cells. In the adult lens, there was an abrupt change in AQP0 antibody binding at the transition zone of differentiating fiber cells with intact nuclei to mature fiber cells without nuclei. AQP1 transcript and protein were detected first in lens anterior epithelial cells at stage E17.5, and in the equatorial epithelial cells around P6.5; the expression increased until P30 and continued through the adult stage both in the anterior and equatorial epithelial cells. The initiation and progression of AQP1 expression occurs simultaneous with the regression of the blood capillaries of lens pupillary membrane, and tunica vasculosa lentis, which nourish the embryonic lens. The lens vasculature starts to regress from late embryonic stage and is complete by P30, which coincides with the increase in AQP1 expression and epithelial cell membrane water permeability.
Lens cell-specific expression of AQP0 and AQP1 suggests different roles in a cell-specific manner. Both are transmembrane water channels, however some other role may account for the differential pattern of expression. Early expression of AQP0 as the primary fiber cells differentiate is consistent with a role in cell-to-cell adhesion. The progressive expression of AQP1 during late embryonic stages and in postnatal lenses may relate to development of the lens internal micro-circulatory system, which become progressively more important as external capillaries regress.
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