Requirement for Pax6 in corneal morphogenesis: a role in adhesion

Abstract

The Pax6 transcription factor functions early during embryogenesis to control key steps in brain, pancreas, olfactory and ocular system development. A requirement for Pax6 in proper formation of lens, iris and retina is well documented. By examining the corneas of heterozygous Small eye (SEY) mice, this report shows that Pax6 is also necessary for normal corneal morphogenesis. In particular, the epithelial component of the postnatal and adult SEY (+/-) cornea is thinner owing to a reduction in the number of cell layers, despite a tenfold increase in the proliferative index and no change in TUNEL labeling. Ultrastructural views revealed large gaps between corneal epithelial cells and a change in the appearance of desmosomes, suggesting that adhesion abnormalities contribute to the corneal phenotype of SEY (+/-) mice. Western blot analysis and immunofluorescence showed equivalent amounts and normal localization of E-cadherin in SEY (+/-) corneas, and the actin cytoskeleton appeared normal as judged by phalloidin staining. By contrast, the levels of desmoglein, β-catenin and γ-catenin were reduced in the SEY (+/-) cornea. In addition, the amount of keratin-12 mRNA and protein, the major intermediate filament, was reduced in SEY (+/-) corneal epithelium as shown by in situ hybridization and immunohistochemistry. Finally, the SEY (+/-) corneal epithelium adheres less well than wild-type when challenged with gentle rubbing using a microsponge. In conclusion, our results indicate that cellular adhesion is compromised in the SEY (+/-) corneal epithelium and suggests a role for Pax6 in the proper generation and maintenance of the adult cornea.

Congenital Aniridia and the Ocular Surface

“…Davis et al have shown large gaps between corneal epithelial cells and an unusual appearance of the desmosomes in Sey mice. 21 These results suggest that desmosomes and the intermediate filaments to which they are attached are abnormal and contribute to the loss of adhesion in the Pax6 +/-mutant cornea.…”

Study of Pax6 mutant rat revealed the association between upper incisor formation and midface formation

“…Second, there may be intrinsic differences in the epithelium of the medial nasal process such as changes in cell adhesion and/or cell survival. Pax6 is involved in cell adhesion or survival in its expressing cells, such as cornea and nasal epithelium (Collinson et al, 2003;Davis et al, 2003;Swanson et al, 2005). Barrier experiments showed that inhibition of fusion resulted in the maintenance of two distinct placodes, and although we were unable to culture the embryos beyond the placode stage, their position was reminiscent of that observed in the rSey 2 mutants, as they were far apart.…”

Dkk2 plays an essential role in the corneal fate of the ocular surface epithelium

“…Epithelial cells of the cornea derive from ectoderm that expresses Pax6, a homeobox gene of profound importance for eye development and maintenance of the cornea (Ramaesh et al, 2003;Davis et al, 2003). In the cornea of mice heterozygous for a Pax6 null mutation, there is decreased expression of keratin K12 and, in addition, conjunctival invasion (Ramaesh et al, 2003;Davis et al, 2003).…”