Resisting the effects of aging: a function for the fiber cell beaded filament.
OBJECTIVE
The beaded filament is a cytoskeletal structure that has been found only in the lens fiber cell. It includes phakosin and filensin, two divergent members of the intermediate filament family of proteins that are also unique to the fiber cell. The authors sought to determine what function the beaded filament fulfills in the lens.


METHODS
Light microscopy and electron microscopy were used to characterize structural changes that occurred in previously generated phakosin and filensin knockout mice. Immunocytochemistry and electron microscopy were used to define the distribution of phakosin, filensin, and beaded filaments.


RESULTS
In phakosin and filensin knockout mice, initial lens development and the early phases of fiber cell differentiation proceed in a manner largely indistinguishable from that of wild type. Fiber cells elongate, undergo organelle elimination, and, in the organelle-free zone, develop the unique paddlelike extensions that characterize cells in this region. Subsequent to those stages, however, fiber cells undergo loss of the differentiated fiber cell phenotype and loss of the long-range stacking that characterizes fiber cells and that has been considered essential for clarity.


CONCLUSIONS
The beaded filament is not required for the generation of the differentiated fiber cell phenotype but is required to maintain that differentiated state and the long range order that characterizes the lens at the tissue level.
Yoon
Kyoung-Hye
KH
Department of Cell Biology and Human Anatomy, School of Medicine, University of California, Davis, California 95616, USA.
Blankenship
Tom
T
Shibata
Bradley
B
Fitzgerald
Paul G
PG
D000375:Aging / Q000502:physiology*; D000818:Animals; D002454:Cell Differentiation / Q000502:physiology*; D005136:Eye Proteins / Q000502:physiology*; D007124:Immunoenzyme Techniques; D007381:Intermediate Filament Proteins / Q000502:physiology*; D007908:Lens, Crystalline / Q000648:ultrastructure*; D051379:Mice; D018345:Mice, Knockout; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D010641:Phenotype; D014746:Vimentin / Q000502:physiology
D005136:Eye Proteins; D007381:Intermediate Filament Proteins; D014746:Vimentin; C079098:filensin; C084808:phakinin