ζ-crystallin: Pax-6 dependence and expression in lens epithelial cells

Purpose. To determine the basis for the gene recruitment and lens-specific expression of guinea pig ζ-crystallin and to develop a new vector for lens targeting of transgenes. Methods. The lens-specific alternative promoter of ζ-crystallin has been analyzed by deletion and footprinting studies and by transfection and transgenic mouse analysis. The expression patterns of ζ-crystallin and Pax-6 were examined by immunohistochemistry. A new vector for lens targeting was constructed using the ζ promoter and 5′ UTR and 3′ flanking sequences from another crystallin gene, γS-crystallin. Results and Conclusions. The ζ-crystallin lens promoter contains a single well-defined binding site essential for expression, the ZPE. Pax-6, apparently alone, binds the ZPE in lens extracts and mutation of the ZPE eliminates both Pax-6 binding and promoter function. Binding, which is principally through the paired domain of Pax-6, causes bending of the ZPE. Sequences upstream of the ZPE also play a role in the promoter, particularly in fine-tuning lens-specificity and eliminating expression in brain. In lens, ζ-crystallin and Pax-6 are both expressed in epithelial cells and the ζ-crystallin promoter is now being used to target transgene expression to mouse lens.