Knock-Out Mice Models: Cornea, Conjunctiva, Eyelids and Lacrimal Gland

Abstract

Many transgenic and knock-out mice exhibit pathogenesis resembling human ocular surface diseases. Thus, the clinical manifestations of mouse lines can be used as clues for identifying inherited human ocular diseases of unknown etiology. However, modified mouse lines using conventional techniques of transgenesis (insertion of an exogenesis gene into an organism such that the gene is transmitted to the offspring) and gene-targeting techniques often exhibit embryonic lethality and congenital defects precluding the use of such mouse models to study acquired ocular surface tissue diseases. Thus, it is vital to have ocular-surface tissue-specific promoters to create mouse models for studying the consequences of loss/gain of a function through transgenesis and gene-targeting techniques. We have identified two cornea-specific genes, keratin 12 (Krt12) and keratocan (Kera), and a Pax6 promoter containing regulatory elements of ocular-surface epithelium-specific expression. We have developed three mouse lines using: (1) keratocan promoter for the preparation of mice in which the promoter is active in ocular surface mesenchymal cells of neural crest origin; (2) knock-in strategies for the Krt12 promoter; and (3) Pax6 promoter to generate mice in which the promoter is active in ocular surface epithelium, that is, cornea, conjunctiva, and lacrimal and meibomian glands. These mouse lines have been bred to obtain double and triple transgenic mice that have inducible gain/loss of functions in corneal keratocyte, corneal epithelium, and ocular-surface epithelium-specific manners. Use of these mouse lines has revealed that excess fibroblast growth factor 7 causes ocular surface squamous neoplasia and the ablation of transforming growth factor-β type II receptor impairs healing of epithelium debridement by delayed activation of p38 mitogen-activated protein kinase. These strategies are of great value to examine the effects of gain and/or loss of functions of other genes.