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M. Leonard, A. S. Menko; -Catenin in Novel Cell Junctions of Differentiating Lens Fiber Cells. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2008.
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© ARVO (1962-2015); The Authors (2016-present)
The lens is one of the earliest cell types demonstrated to express γ-catenin (plakoglobin). We now have examined the role of γ-catenin in novel cell junctions of differentiating lens fiber cells.
Co-immunoprecipitation (IP) analysis was used to determine the composition of γ-catenin containing junctions in microdissected E10 chick embryo lenses. Cytoskeletal linkage of these junctions was determined by sequential extraction in Triton-Octylglucoside (OG/T), and SDS buffers followed by western blot analysis. To demonstrate the presence of three proteins (i.e. cadherin/catenin/cytoskeleton) within the same adhesion complex, we developed a new double IP technique involving sequential IP of complex components.
The assembly of N-cadherin junctions is necessary for lens cell differentiation, and stabilization of these junctions is important for the formation and maintenance of lens cytoarchitecture. Both ß-catenin and γ-catenin can bind directly to N-cadherin however, only γ-catenin is recruited to N-cadherin junctions in a differentiation specific manner. As such, γ-catenin is likely to play a critical role in the stabilization of N-cadherin junctions. Using differential detergent fractionation, we have previously identified an OG/T insoluble, SDS soluble fraction in fiber cells of the E10 lens. This fraction was enriched not only with intermediate filament proteins such as vimentin, but also N-cadherin and γ-catenin. Co-IP studies revealed that N-cadherin was associated with vimentin in this fraction. We now show that γ-catenin is also highly associated with vimentin in differentiating lens cells. Sequential co-IP has led to the discovery of a novel N-cadherin/γ-catenin vimentin intermediate filament linked junction in differentiating lens fiber cells. Interestingly, while γ-catenin can associate with ß-actin, the N-cadherin/γ-catenin junction does not appear to associate with ß-actin. This indicated that γ-catenin may be present in another adhesion complex. Investigation of other adhesion proteins to which γ-catenin was linked led us to the surprising discovery that γ-catenin was associated with α6 integrin, and that this association was differentiation-specific. This is the first demonstration of the association of γ-catenin with an integrin, and may indicate a role for γ-catenin in integrin-cadherin crosstalk in differentiating lens fiber cells.
Our data indicates that γ-catenin is a critical component of differentiating lens fiber cells, providing junctional stability to N-cadherin junctions via linkage to vimentin, and may have a role in integrin-cadherin crosstalk.
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