Corneal Epithelial Cell Fate and Stratification Abnormalities Observed Following Conditional Deletion of AP-2B in the Neural Crest Cells of the Mouse

Abstract

The cornea is an anterior eye structure that is specialized to be transparent. It is comprised of an endothelial monolayer, avascular stroma and stratified epithelium. Anterior ocular tissues, including the corneal endothelium and stroma, develop from the periocular mesenchyme (POM), which derives from neural crest cells (NCCs). Activating Protein-2B (AP-2B) is highly expressed in the POM. Our lab has used a conditional knock- out model in which AP-2B is deleted in the NCCs, known as the AP-2B NCC KO mouse, to investigate the role of this protein in anterior segment development. In these mutants we previously observed a closed iridocorneal angle, as well as corneal abnormalities including an absent endothelium, stromal neovascularization, and failed epithelial stratification. The present thesis sought to investigate corneal defects in the AP-2B NCC KO mouse, and particularly the corneal epithelium given that it arises from the surface ectoderm rather than POM. PAS and IHC staining showed changes to epithelial cell fate and stratification. We observed that Keratin-12, a marker of differentiated corneal epithelium, was absent, and Keratin-15, a limbal and conjunctival marker, was expanded across the epithelium. Changes to the basement membrane and integrin expression were also evident. Given the non-NCC origin of the epithelium we hypothesize that abnormalities in the corneal epithelium of the AP-2B NCC KO mouse result from changes to regulatory signaling from the POM-derived stroma. Our investigation of Wnt/B-Catenin signaling suggested an important role for this pathway through its interactions with growth factor Bmp4, which is supressed in the mutant. Ultimately these results indicate that AP-2B expression in the POM is crucial for normal corneal epithelial cell fate and stratification.