Quantitation of PAX6 and PAX6(5a) transcript levels in adult human lens, cornea, and monkey retina

Purpose: PAX6 is a critical regulator of the developing lens, other ocular tissues, central nervous system, and pancreas. There are two alternatively spliced forms of the protein, PAX6 and PAX6(5a), that may have different re gulatory functions. This study was designed to determine the amounts of PAX 6 and PAX6(5a) transcripts present in adult human lens epithelium and fiber s, human cornea and monkey retina. Methods: PAX6 and PAX6(5a) transcript levels were monitored in microdissect ed lens epithelia, lens fibers, whole lens, cornea, and retina by competiti ve RT-PCR. The levels of TBP/TFIID were examined in adult human lens epithe lium and fibers as control. Results: PAX6 and PAX6(5a) were expressed at equal levels in lens epitheliu m and fibers. Ninety-five times more PAX6 transcripts were detected in the epithelial cells than in the fibers. Adult human cornea and monkey retina e xpressed less PAX6/PAX6(5a) than lens epithelium but more than lens fibers. Correspondingly, 40 fold higher levels of TBP transcripts were detected in lens epithelium than fibers, suggesting reduced overall expression of tran scription factors in the adult lens fibers. Conclusion: The presence of PAX6 and PAX6(5a) messages and proteins in adul t lens epithelium suggest functions for both forms of PAX6 in the growth an d maintenance of the adult human lens. The reduced levels of both forms of PAX6 in the lens fibers suggest down regulation of this gene during differe ntiation of epithelia into fibers. The lower level of TBP expression in len s fibers also suggests reduced transcriptional competence of adult lens fib ers.