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Katsuhiko Shinomiya, Satoshi Kawasaki, Shigeru Kinoshita; Exceptional Pairing of Type I and Type II Keratin Molecules in Human Ocular Surface Epithelia, An Implication for New Keratin-Pairing Model. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1947.
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© ARVO (1962-2015); The Authors (2016-present)
Keratins are molecules constituting an intermediate filament that functions as a cytoskeleton of various kinds of epithelial cells. Keratins are classified into acidic type I and basic type II from their molecular weights and isoelectric points, and type I keratin binds to type II keratin in an equimolar ratio. Previous studies have revealed the existence of specific partners for each keratin molecule from the observation of the specific expression pattern of those molecules in various kinds of tissues. However, when we investigated the expression of keratin molecules in ocular surface epithelia, we sometimes experienced some exceptional findings that were difficult to explain based on the list of the established keratin pairing. In the present study, some combinations of keratin molecules were investigated in the corneal and limbal epithelia by the use of proximity ligation assay (PLA) for the analysis of molecular proximity.
Immunofluorescence staining was performed on a frozen section of human corneal tissue with anti-keratin 3, 4, 5, 12, and 13 antibodies. PLA analysis was performed for some selected combinations of the above-listed antibodies on that frozen section using a commercially available PLA kit.
The PLA signal was observed in almost all layers of the corneal and limbal epithelia for the combination of keratin 3 and 12 as well as that of keratin 5 and 12. For the combination of keratin 4 and 12, the PLA signal was observed only at the surface of the corneal and limbal epithelia. Interestingly, although it was only in a small number of cells, the PLA signal was observed even in the combination of keratin 12 and 13 for all they are both type I keratin.
Keratin molecules are known to exert various kinds of cellular functions rather than simply function as a component of cytoskeleton. Our current study implies the possibility for the novel keratin pairings in the ocular surface epithelia in addition to those which has already been established. Such keratin pairs may be involved the unique and specific functions of intermediate filament in the ocular surface.
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