DIFFERENTIAL-EFFECTS OF AQUEOUS AND VITREOUS ON FIBER DIFFERENTIATIONAND EXTRACELLULAR-MATRIX ACCUMULATION IN LENS EPITHELIAL EXPLANTS

Purpose. Results from this and other laboratories strongly suggest tha t differences in the properties of the ocular media that bathe cells i n the anterior and posterior regions of the lens contribute to its nor mal growth patterns and polarity. The aim of this study was to compare the effects of aqueous and vitreous on the morphology of lens epithel ial explants, with particular attention to changes associated with fib er differentiation. Methods. Light and electron microscopy were used t o assess rat lens epithelial explants cultured with bovine aqueous or vitreous. Immunohistochemistry was used to detect fiber-specific cryst allins and extracellular matrix components, and synthesis of extracell ular matrix was investigated by autoradiography. Results. Vitreous, bu t not aqueous, induced morphologic changes characteristic of fiber dif ferentiation, which included cell elongation, organelle loss, and the appearance of ball and socket junctions, as well as the accumulation o f beta-crystallin. In addition, vitreous stimulated the synthesis and organization of a distinct basement membrane on explants that resemble d the lens capsule, both structurally (regular layers of basal laminae ) and immunologically (reactive for laminin and heparan sulphate prote oglycan). Conclusions. Only one of the ocular media, the posteriorly l ocated vitreous, induced lens epithelial explants to undergo morpholog ic events characteristic of fiber differentiation. This provides furth er support for the hypothesis that anteroposterior patterns of cellula r responses in the lens are caused by differences in the ocular media. The observation that vitreous also stimulated the synthesis and assem bly of capsule-like extracellular matrix suggests that vitreous contai ns factors that may influence lens capsule formation in situ.