Cell-cell interactions affect the accumulation of a cytokeratin-like protein during lens fiber development.

Extracellular matrix proteins were presented in culture to postmitotic, epithelial precursors of chick lens fiber cells as rigid, planar surfaces or malleable gels. Their ability to maintain and promote differentiated characteristics was judged by tritiated thymidine incorporation, immunologic detection of a cytokeratin-like protein (CP49) which accumulates during lens fiber development, and the formation of multicellular aggregates known as lentoids. Regardless of their composition, planar substrates stimulated the reentry into the cell cycle by promoting cell spreading. Laminin- and type IV collagen-coated surfaces facilitated monolayer growth and no appreciable accumulation of CP49. Thin films of Matrigel, which initially stimulated cell division, eventually promoted the formation of extensive lentoids, multicellular aggregates exhibiting many morphologic and biochemical properties of lens fibers. Malleable gels of Matrigel, however, inhibited cell division and immediately allowed the cells to begin lentoid formation. Culture conditions which favored lentoid formation also showed greatly enhanced levels of CP49 accumulation. In addition, lentoids were also shown to accumulate an integral membrane protein (MIP26) which is present in communicating junctions between neighboring fiber cells. These studies indicate that increased cell associations within forming lentoids may influence the progression of lens fiber terminal differentiation in vitro.