Organization of $\beta\sb1$ integrin and N-cadherin mediated adhesion complexes during lens cell differentiation
The organization and requirement of adhesion complexes for lens cell differentiation was studied. The cell adhesion receptors, $\beta\sb1$ integrin and N-cadherin, link to the cytoskeleton via a complex of proteins associated with their cytoplasmic domain. The organization of these adhesion complexes was evaluated by Triton-X-100 extraction and immunoblotting the Triton insoluble fraction which allows for the determination of components associated with the cytoskeleton. The cytoskeletal association of $\alpha$-actinin and vinculin in the central epithelium suggests that these adhesions are stable. In contrast, talin and FAK associated with $\beta\sb1$ integrin mediated adhesion complexes in the equatorial epithelium and cortical fiber cells reflects the migratory nature of these populations. These regions are undergoing differentiation and the cytoskeletal association of FAK and paxillin implies a role for $\beta\sb1$ integrin-mediated signaling in differentiation. In the differentiated central fiber cells, the cytoskeletal association of cadherins and vinculin implies that these cell-cell adhesion complexes are stabilized. The cytoskeletal association of paxillin in the central fiber cells but not $\beta\sb1$ integrin, talin or FAK implies it functions as an adaptor protein in terminal fiber cell differentiation.^ Tatin and FAK, but not vinculin, were tyrosine phosphorylated in the lens but tyrosine phosphorylation did not regulate their association with adhesion complexes. Interestingly, the existence of adhesion complexes partially assembled when not linked to the cytoskeleton; specifically, FAK-talin-vinculin-paxillin complexes, suggests that pre-assembled complexes are inserted into forming adhesion complexes in a modular fashion to facilitate their rapid assembly.^ The role of $\beta\sb1$ integrin's cytoplasmic domain was evaluated in lens cultures by transfection of a cytoplasmic domain deletion mutant. Transfected cells were excluded from lentoids, the in vitro equivalent of lens fiber cells, suggesting that $\beta\sb1$ integrin function and its associated adhesion complexes are required for lens differentiation.^ To ascertain the role of N-cadherin's cytoplasmic domain in the lens, transgenic mice were generated with an N-cadherin cytoplasmic domain truncation mutant under control of the $\alpha$A-crystallin promoter for lens specific expression. This mutant should inhibit N-cadherin function in a dominant-negative manner demonstrating the requirement of N-cadherin mediated adhesion complexes for lens differentiation. Several founder animals were produced. ^
Biology, Molecular|Biology, Cell|Health Sciences, Ophthalmology
Robert William Veneziale,
"Organization of $\beta\sb1$ integrin and N-cadherin mediated adhesion complexes during lens cell differentiation"
(January 1, 1998).
ETD Collection for Thomas Jefferson University.