Abstract
Purpose: :
Lens fibers must differentiate, elongate and migrate in order for the lens to develop properly. These processes are dependent on adhesion of the lens fibers to the anterior epithelium, to the posterior lens capsule and to other lens fibers. Key adhesion proteins thought to be involved in this process include fibronectin (fn), an extracellular matrix (ECM) protein, and integrin5 (itg5), a transmembrane protein capable of binding to both ECM and cytoskeletal proteins. Zebrafish with recessive mutations in fn and itga5 have been identified previously, and the purpose of this study was to analyze their lenses and determine if Itg5/Fn dependent adhesion was required for normal lens development
Methods: :
Parallel experiments were conducted on zebrafish mutations for fn and itga5. Mutant lenses were examined using histology, immunohistochemistry, in situ hybridization, transmission electron microscopy (TEM) and in vivo time-lapse confocal imaging.
Results: :
Histology and TEM of fn and itga5 mutants indicated that lens fibers did not adhere to the anterior epithelium, and that newly generated fibers did not adhere to each other at the lens equator. Actin organization, assayed both in fixed tissue and in vivo, was disrupted in fn and itga5 mutants. The normal differentiation of lens fibers is marked by expression of crystallin β4 in control lenses. fn and itga5 mutants, however, lacked this spatial specificity and expressed crystallin β4 throughout the anterior epithelial layer. Finally, mutant lenses did not show increased numbers of apoptotic cells when compared to sibling controls.
Conclusions: :
These results indicate that Fn and Itg5 are required for adhesion of lens fiber cells to the anterior epithelium, and to each other. Itg5/Fn adhesion activates intracellular signaling cascades and our in situ data support a model whereby Itg5/Fn interactions prevent ectopic lens fiber differentiation within the anterior lens epithelium. Itg5/Fn interactions are important for elongation and migration of cells - processes that require extensive cytoskeletal rearrangements. Our data indicate that Itg5/Fn interactions are required for proper cytoskeletal organization within lens fibers.
Keywords: development • cell adhesions/cell junctions • cataract