VIMENTIN AND CP49 FILENSIN FORM DISTINCT NETWORKS IN THE LENS WHICH ARE INDEPENDENTLY MODULATED DURING LENS FIBER CELL-DIFFERENTIATION

The cells of the eye lens contain the type III intermediate filament p rotein vimentin, as well as two other intermediate filament proteins, CP49 and filensin. These two proteins appear to be unique to the diffe rentiated lens fibre cell, Immunoblotting and confocal microscopy were used to describe changes which occur in these three intermediate fila ment proteins and the networks they form during fibre cell differentia tion and maturation. The vimentin network was present in both epitheli al cells and some fibre cells, Fibre cells were vimentin positive up t o a specific point 2-3 mm in from the lens capsule where the vimentin signal was drastically reduced, The CP49/filensin network was not pres ent in the undifferentiated epithelial cells but emerged in the differ entiating fibre cells, This latter network exhibited a principally pla sma membrane localization in younger fibre cells but became more cytop lasmic in older fibre cells. This change also occurred at a distinct p oint in fibre cell differentiation, much earlier than the observed los s of the vimentin network, The subcellular changes in the distribution s of these cytoskeletal networks were correlated to the loss of the fi bre cell nucleus, another feature of fibre cell differentiation. No co rrelation was found to changes in the vimentin network but nuclear los s did coincide with changes in the CP49/filensin network. Concomitant with nuclear pyknosis, there were also changes in the nuclear lamina a s well as infringement of the nuclear compartment by CP49, as shown by confocal microscopy, This study demonstrates vimentin and the CP49/fi lensin network to be independent in the lens but both networks undergo dramatic changes in subcellular distribution during the differentiati on/maturation of the fibre cell, Only changes in the CP49/filensin net work can be correlated to nuclear loss. Thus in the lens, unlike mamma lian erythropoiesis which is also characterized by nuclear loss, the v imentin network does not appear linked to nuclear retention.