Changes in adhesion complexes define stages in the differentiation of lens fiber cells.

PURPOSE During their differentiation, lens fiber cells elongate, detach from the lens capsule, associate at the sutures, and degrade all cytoplasmic membrane-bound organelles. Changes in the expression or organization of cell adhesion and cytoskeleton-associated proteins were correlated with these events during fiber cell differentiation in chicken embryos. METHODS Fixed or living lenses were sliced with a tissue slicer, permeabilized or extracted with detergents, stained with antibodies or fluorescent-labeled phalloidin, and viewed with a confocal microscope. The distribution of N-cadherin in elongating and mature fiber cells was determined by Western blot analysis. Reverse transcription-polymerase chain reaction (RT-PCR) was used to determine the distribution of vinculin and paxillin transcripts. RESULTS Staining for N-cadherin and band 4.1 protein decreased soon after fiber cells detached from the capsule. Detergent extraction of lens sections and Western blots of dissected lens regions showed that much of this decrease in staining was due to epitope masking. Vinculin immunoreactivity was barely detectable on the lateral membranes of elongating fiber cells but increased markedly once these cells reached their maximum length and formed the sutures. Staining for paxillin was also low in elongating fiber cells but increased late in fiber cell differentiation, just before the cells destroyed their membrane-bound organelles. Spectrin and ankyrin immunoreactivity did not change when fiber cells reached the sutures. Staining for F-actin increased transiently in cells that had just reached the sutures. Messenger RNAs for vinculin and paxillin were more abundant in maturing than in elongating fiber cells. CONCLUSIONS The adhesion complexes of lens fiber cells change in organization and composition soon after these cells finish elongating and detach from the capsule. Increased staining for vinculin and paxillin defines distinct stages of fiber cell differentiation that are intermediate between the completion of cell elongation and the time when lens fiber cells degrade their membrane-bound organelles. Remodeling adhesion complexes during fiber cell maturation may assure the stability of fiber-fiber associations, once these cells are no longer transcriptionally active.