Differential expression of connexin 43 in limbus and corneal epithelium suggests gap junction role in corneal epithelial differentiation

Purpose. Communication through gap junctions have been shown to play critical roles in development and differentiation. The basal cells of the corneal epithelium have a high density of connexin 43 (Cx43), a gap junction protein isoform. Accordingly, the purpose of this study was to identify changes in the distribution of this isoform along the limbo-corneal differentiation path. Methods. Human, rabbit and chicken corneas were frozen in liquid nitrogen, sectioned (10μ thick) and immunostained for connexin 43. Sections were also stained for corneal specific cytokeratin K12, in order to identify, unequivocally, the limbal region. Results. In all three species Cx43 is present in the basal cells of the corneal epithelium, but is absent from the limbal region. In the rabbit, the discrete connexin 43 membranous staining is maximal at the limbal-proximal peripheral zone associated with the transient amplifying cells and decreases gradually towards the center. The increase from the limbus-free to the zone of maximal expression occurred gradually, i.e. in the first 5-10 limbal-proximal cells one could see only 1-2 discrete junctions per cell. The number of junctions then increase gradually to reach up to 10 discrete spots per cell. Conclusions. Limbo-corneal differentiation involves de novo synthesis of Cx43. Since hetero-typical gap junctions may exhibit impaired communications, even if it turns out that the limbal cells express other connexins, the present results raises the possibility of a cell-to-cell communication discontinuity between the stem limbal cell population and their differentiating corneal progeny.