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P. Charukamnoetkanok, Y. Sado, N. SundarRaj; Differential Expression of Type IV Collagen Isoforms: Implications for Stem Cell Niche . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2101.
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Purpose: Basement membrane is an important component of the stem cell microenvironment (niche). Type IV Collagen is an essential constituent of corneal basement membrane. This study evaluated differential expression of type IV collagen isoforms (α–1,2,3,4,5,6) in the human central cornea and limbus. Methods: Frozen sections of normal human cornea were treated with acetone and 6 M urea in 0.1 M glycene–HCl buffer (pH 3.5). Immunohistochemistry was performed using rat antihuman monoclonal antibodies against specific isoforms of type IV collagen. Observations were made using confocal fluorescence microscopy. Results: α1 and α2 (IV) collagens were detected only in the limbus and perivascular region. α3 and α4 (IV) collagens were most abundantly located in the central cornea. Interestingly, α3 isoform showed unique punctate pattern of expression in the limbal region. The regions devoid of α3 isoform also lacked K3 keratin expression. α5 and α6 collagens were expressed in both the central cornea and limbus. All isoforms were present in the Descemet’s membrane but had different distribution pattern. Conclusions: Isoforms of type IV collagen exhibited differential expression in the central cornea and limbus. The absence of K3 expression in the cells located over the regions of basement membrane devoid of α3 (IV) collagen raises a possibility that these specialized regions may represent the stem cell niche, and the lack of α3 (IV) expression may be another distinguishing feature of corneal epithelial stem cells.
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