LENS EPITHELIAL-CELL MESSENGER-RNA .3. ELEVATED EXPRESSION OF MACROPHAGE-MIGRATION INHIBITORY FACTOR MESSENGER-RNA IN GALACTOSE CATARACTS

A lens epithelial (LE) cell cDNA clone, designated Clone 156, was isol ated from a mature rat LE cDNA library by methods of subtractive hybri dization. The cDNA sequence of Clone 156 was 521 nucleotides in length , excluding the poly(T)-tail, and it encoded an open reading frame of 115 amino acids. The translated protein shared extensive sequence simi larities with macrophage migration inhibitory factor (MIF) from mouse lens and human T-cell lymphocytes. Northern blot hybridization showed that rat lens MIF mRNA is about 500 nucleotides in length and that its expression in mature rat lens is relatively low in comparison with th at in other rat tissues. The expression of MIF mRNA in LE of normal ra ts and of rats treated by feeding a diet of 50% (w/w) galactose was st udied by quantitative RT-PCR. The results showed that the expression o f MIF mRNA in a 20-day galactosemic rat LE increased twelvefold as com pared to that found in control LE. From the results of this study and from what we know about the locale of epithelial cell differentiation in mature rat lenses, it is being proposed that the increase in abunda nce of MIF mRNA in the cataractous rat lens is correlated with the enh anced proliferation of the undifferentiated epithelial cells.