THE PAX-6 HOMEOBOX GENE IS EXPRESSED THROUGHOUT THE CORNEAL AND CONJUNCTIVAL EPITHELIA

Purpose. Heterozygous defects in the highly conserved PAX6 homeobox ge ne are associated with aniridia, an inherited human disorder affecting several ocular structures, including the adult cornea. This work esta blishes the pattern of Pax-6 gene expression in the surface epithelia of the late embryonic and adult eve. Methods. Chick embryo sections an d wholemounts, as well as adult mouse and monkey tissues, were analyze d by in situ hybridization and immunohistochemistry with probes specif ic to Pax-6. Western immunoblots were used to detect Pax-6 protein, an d mRNA expression Nas analyzed by quantitative reverse transcription-p olymerase chain reaction. Results. In days 5 and 6 chick embryos, Pax- 6 protein is found in the nuclei of all cells within the corneal epith elium and in the future conjunctiva. Although not detected in the corn ea by in situ hybridization, Pax-6 mRNA is, in fact, present at levels comparable to those observed in the retina. In the mature mouse, Pax- 6 protein was expressed in all cells of the corneal epithelium, the li mbus, and the entire conjunctiva. Similar results were obtained for th e monkey cornea. Conclusions. These data indicate that in addition to its role in the embryo, Pax-6 is expressed strongly in surface epithel ia of the adult cornea and conjunctiva. In cells of these tissues, the gene may function by regulating structural or secretory specializatio ns. Pax-6 might play a direct role in the maintenance and proliferatio n of corneal stem cells, a vital process that appears to be defective in aniridia.