Development- and differentiation-dependent reorganization of intermediate filaments in fiber cells

PURPOSE. TO define the remodeling of lens fiber cell intermediate filaments (IF) that occurs with both development and differentiation. METHODS. Prenatal and postnatal mice were probed for the IF proteins phakos in, filensin, and vimentin, using light microscope immunocytochemical metho dology. RESULTS. The pattern of vimentin accumulation in elongating fiber cells cha nged with development. Early in development vimentin first emerged predomin antly as focal accumulations in the basal region of both epithelial and pri mary fiber cells. A light diffuse cytoplasmic staining was also noted. Late r in embryonic development, and through maturity, vimentin in fiber cells w as predominantly associated with the plasma membrane with no anterior-poste rior polarity. Phakosin and filensin were first detected in the very latest stages of primary fiber elongation and continued to accumulate well after cells had completed elongation. Initially, these proteins accumulated in th e anterior half of the fiber cells and were cytoplasmic in distribution. Af ter P13, the pattern of initial distribution in differentiating fiber cells changed to a predominantly plasma membrane localization. Neither beaded fi lament protein showed focal basal accumulations. In mature lenses, all thre e proteins ultimately disappeared from the nuclear fiber cells. CONCLUSIONS. Beaded filament protein accumulation lags significantly behind both primary and secondary fiber cell elongation, suggesting a functional role subsequent to elongation. The subcellular distribution of vimentin and the beaded filament proteins showed marked differences within the cell, wi th differentiation, and with development. The differences in time of initia l synthesis and in distribution of these IF proteins map bear on hypotheses about the role of Ifs in fiber cell elongation and in structural-functiona l polarity of the fiber cell.