MP26 messenger RNA sequences in normal and cataractous lens. A molecular probe for abundance and distribution of a fiber cell-specific gene product.

Previous work from this laboratory has suggested that swollen nucleated fiber cells can survive in mature galactose-cataracts. Evidence for this observation was derived from analysis on the in vitro translation products of mRNA isolated from normal lens and lens undergoing development of galactose-cataracts. Therefore, studies on the fate of a fiber cell-specific gene product (MP26 mRNA) in both normal and cataractous lens should map out gene response to: (1) differentiation of epithelial cells to fiber cells; (2) levels of this differential gene activity and its anatomical location in initiation and maturation of galactose-cataracts; and (3) distribution of MP26 and mRNA in fibers of normal and cataractous lens. The MP26 probe was isolated by methods of cDNA cloning into expression vectors, then subcloned into a transcription vector, and the recombinant plasmid was transcribed into sense and anti-sense [35S]-UTP-labeled RNA. The [35S]-labeled RNA products were used to localize MP26 mRNA in tissue sections by methods of hybridization in situ. The results on normal lens show that gene transcription for MP26 mRNA is initiated immediately in elongating fibers, where new fiber cell nuclei begin to migrate to within the cortex. The MP26-positive grains are absent from the epithelium, highest at the bow, with a lower number in fibers below the posterior capsule, and lowest in the lens nucleus. The cataractous lens exhibits continued manifestation of MP26 mRNA at the bow, but at significantly lower concentrations than found in the controls, and this low level persisted in viable areas of the cortex. Absence of significant grains in areas containing cell debris is evident. The emerging picture for MP26 mapping in lens suggests that: (1) in cataractous as well as in normal lens MP26 mRNA first develops in elongating fibers; and (2) that MP26 mRNA localization gives an exact measure of point of cell specialization, and levels or "storage" of a specific gene product in fiber cells undergoing maturation, aging and cataractogenesis.