THE INTERMEDIATE FILAMENT CYTOSKELETON OF THE LENS - AN EVER-CHANGINGNETWORK THROUGH DEVELOPMENT AND DIFFERENTIATION - A MINIREVIEW

In the eye lens, intermediate filament proteins form two morphological ly distinct polymers, 10-nm intermediate-sized filaments and beaded fi laments. Coincidently, the beaded filament polymer and the proteins fi lensin and CP49 are specific to lens fibre cells and are therefore exc ellent markers for fibre cell differentiation. In the adult lens, file nsin and CP49 are maintained throughout all stages of lens fibre cell differentiation whilst vimentin is apparently lost at a specific stage from the deeper cortical fibres. The expression of CP49 and filensin is coincident with the presence of beaded filaments suggesting these p roteins are filament components. In association with alpha-crystallin, CP49 and filensin form beaded filaments in vitro. During fibre cell d ifferentiation, filensin and CP49 are post-translationally modified. I n the case of filensin, proteolysis results in two functionally distin ct fragment sets, one derived from the a-helical rod domain and the ot her from the C-terminal tail domain of filensin. It is proposed that b oth filensin and CP49 are critically involved in organising the cytopl asmic and plasma membrane domains of the fibre cell and therefore esse ntial to the optical properties of the lens.