Crystallin synthesis and crystallin mRNAs in galactosemic rat lenses

Abstract

Changes in crystallin synthesis and crystallin mRNA content were followed in the epithelial and fiber cells of rat lenses during the development and reversal of galactose cataracts. Crystallin synthesis was not lowered in the lens epithelial cells throughout the 18 days of galactose feeding. By contrast, crystallin synthesis appeared partially reduced in the fiber cells of cultured lenses after the rats had been on a diet of 50% galactose for 6 days, and was essentially arrested in the lens fiber cells after the rats were fed galactose chow for 12 or 18 days. In vitro translation tests in a rabbit reticulocyte lysate demonstrated that control lenses contained α-, β- and γ-crystallin mRNAs in the cortical and nuclear fiber cells. The lens fiber cells of the 6-day galactosemic rats still possessed a full complement of crystallin mRNAs but those of the 15-day galactosemic rats had no detectable crystallin mRNAs. After 12 days the galactosemic lenses had lost approximately half of the crystallin mRNAs from the cortical fiber cells and all of the mRNAs from the nuclear fiber cells. Both crystallin synthesis and crystallin mRNA content recovered in the cortical fiber cells, but not in the nuclear fiber cells, during reversal of the galactose cataract. These results indicate that the reduction in crystallin synthesis is confined to the fiber cells and occurs initially by a decreased efficiency of utilization of crystallin mRNAs and subsequently by the degradation of the mRNAs. Previous experiments provide evidence that the impaired utilization of the crystallin mRNAs is due to the alterations in electrolytes in the cataractous lenses.