Abstract
Purpose: :
Lens fiber cells assemble a fiber cell–specific derivative of the intermediate filament, referred to as the beaded filament. Targeted deletion of proteins required for beaded filament assembly result in a subtle loss of lens clarity. In this study we sought to determine the relationship between fiber cell structural differentiation and the loss of the beaded filament.
Methods: :
Wildtype and beaded filament knockout mice were compared by scanning electron micrscopy, histology, laser microdissection and QPCR.
Results: :
Wildtype mice assemble unique specializations of fiber cell surface that are much larger in scope than the commonly described "ball–and–socket" interdigitations. These appear late in differentiation, after the fiber cell has lost its organelles, then regress shortly thereafter. These specializations are only present in the middle region of the fiber cell and are absent from the anterior and posterior ends. They are not present at birth and first emerge at about two weeks post natal, in both wildtype and beaded filament knockout mice.
Conclusions: :
The fiber cell is capable of extensive structural differentiation after the cell has lost its organelles, in both wildtype and knockout mice. The knockout mouse, however, shows a reduced capacity to maintain the elaborate structural differentiation and long range order that characteizes the fiber cells of the wild type lens, suggesting that the beaded filament is not required to achieve structural differentiation, but is required to maintain it.
Keywords: cell membrane/membrane specializations • differentiation • cytoskeleton