Lens intermediate filaments

Abstract

The ocular lens assembles two separate intermediate filament systems sequentially with differentiation. Canonical 8-11 nm IFs composed of Vimentin are assembled in lens epithelial cells and younger fiber cells, while the fiber cell-specific beaded filaments are switched on as fiber cell elongation initiates. Some of the key features of both filament systems are reviewed.

Figure 1

Schematic view of the consensus predicted secondary structure of the IF protein, along with that predicted for CP49 and filensin.

Figure 2

2A: Immunoflurescent localization of vimentin in a paraffin section of mouse lens fixed by freeze substitution in 97% methanol:3% acetic acid. 2B: In situ hybridization localizing vimentin mRNA in paraffin sections of mouse lens. 2C: Immunoperoxidase localization of CP49 in paraffin section of mouse lens, fixed as in 2A. 2D: In situ hybridization demonstrating distribution of CP49 mRNA in mouse lens.

Figure 3

Electron micrograph of ghosted mouse lens, showing a tangential view of a fiber cell membrane (arrow) where IFs are aligned along the surface of the membrane.

Figure 4

Scanning electron micrographs of a wild type (A) and BF knockout (B) lens. Figure A is a lower magnification overview, with an arrow highlighting the transition from a region where the paddle-like structures are regressing. Deep to this point, fiber cells retain their unique shape and strict alignment. Figure B is a higher magnification view of a BF knockout lens, with an arrow placed at a similar transition point. The loss of fiber cell shape and alignment at this juncture is evident in the knockout.