Résumé
Cornea is the outermost surface of the eye that refracts light to the lens and protects the sensitive ocular machinery. The cornea is divided to three cellular compartments; epithelium, stroma and endothelium. Our work focuses on the corneal epithelium, which is located closest to the tear film and, together with the film, forms a physiological barrier to pathogens and small particles from the environment. We followed the maturation of the mouse corneal epithelium from birth to adulthood and discovered a novel marker, Krt19, in this process. Krt19 expression gradually restricted from the central cornea to the limbus, concomitantly with eyelid opening and epithelial stratification, which are the hallmarks of postnatal maturation of the murine cornea. Corneal epithelium is renewed continuously throughout life by stem cells. Previous studies demonstrated that the limbus, located in the periphery of the cornea, houses the corneal stem cells. Immediate progeny of the stem cells, the progenitor cells, localize to the limbus, peripheral, and central cornea. We identified the gene Bmi1 in the corneal, epithelial progenitor cells. By lineage tracing of the Bmi1+ cells, we followed renewal dynamics in the central cornea and estimated the turnover of the epithelium to be 2-8 weeks in adult mice. However, we noticed a decrease in renewal rate with older animals. This is in line with evidence from renewal studies of the limbal stem cells, suggesting a general decrease of corneal epithelial renewal upon aging. We optimized a method to perform in vivo epithelial abrasion injury on mouse cornea. The development of this assay was instrumental for the experiments that followed. Using the abrasion model, we showed that the Bmi1+, central, corneal progenitor cells do not contribute to wound healing. Instead, the wound closed by rearrangement and migration of the remaining epithelial cells. We extended our analysis of the corneal barrier to encompass an accessory organ of the eye, the lacrimal gland (LG, tear gland). LG produces and secretes the aqueous part of the tear film, which is the largest portion of the film. The tear film provides another layer of protection to the ocular surface, because it contains anti-inflammatory and antimicrobial components as well as assists eyelid movements. We studied the role of Ectodysplasin-A (Eda) gene in the LG. Eda is critical in the development of ectodermal appendages, however LG development was not affected by the loss-of-function mutation in Eda. Instead, lack of EDA resulted in modulation of LG secretion and the development of a dry eye disease (DED). Furthermore, we discovered that Eda signalling activity was inhibited in response to corneal injury and suggest that this is necessary for the production of reflex tears that are released in ocular insult. In this assay, we shed light on the cooperation between cornea and the LG in homeostasis and injury. Our work is part of the research that aims to understand maturation and homeostatic maintenance of the anterior segment of the eye, cornea and the LG. This work provides new information regarding the development of Eda-linked DED. This is of importance, because the DED affects a large part of the population. Furthermore, we call for further studies on the mechanisms of how these two tissues communicate, as they are intricately linked and dependent of each other.