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 regulatory functions. This study was designed to determine the amounts of PAX6 and PAX6(5a) transcripts present in adult human lens epithelium and fibers, human cornea and monkey retina.
Methods: PAX6 and PAX6(5a) transcript levels were monitored in microdissected lens epithelia, lens fibers, whole lens, cornea, and retina by competitive RT-PCR. The levels of TBP/TFIID were examined in adult human lens epithelium and fibers as control.
Results: PAX6 and PAX6(5a) were expressed at equal levels in lens epithelium and fibers. Ninety-five times more PAX6 transcripts were detected in the epithelial cells than in the fibers. Adult human cornea and monkey retina expressed 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 transcription factors in the adult lens fibers.
Conclusions: The presence of PAX6 and PAX6(5a) messages and proteins in adult lens epithelium suggest functions for both forms of PAX6 in the growth and 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 differentiation of epithelia into fibers. The lower level of TBP expression in lens fibers also suggests reduced transcriptional competence of adult lens fibers.