This project seeks to determine whether lens fiber differentiation is associated with alterations in plasma membrane lipids or proteins. Previous results have indicated that phosphatidylinositol degradation ceases when lens epithelial cells differentiate to form lens fiber cells. Since phosphatidylinositol is rich in arachidonic acid, a precursor of prostaglandins and leukotrienes, the metabolites of arachidonic acid produced by lens cells are being characterized. Comparison of metabolites synthesized before and after the onset of fiber cell formation demonstrates that the loss of a lipoxygenase pathway metabolite is associated with differentiation and the concommitant increase in c-myc mRNA. Plasma membrane proteins being investigated include the insulin and IGF receptors, and the membrane associated protein calpactin I. Specific insulin and IGF receptors have been demonstrated on both lens epithelial cells and lens fiber cells throughout embryonic development; a marked decrease in insulin receptors is associated with fiber cell formation. Calpactin I has been shown to be a major component of the EDTA extractable protein (EEP) of lens membranes. This protein binds both phospholipids and actin, and may thus be involved in anchoring the cytoskeleton of the lens to the membrane.
