STEM-CELLS OF THE CORNEAL EPITHELIUM LACK CONNEXINS AND METABOLITE TRANSFER CAPACITY

The stem cells of the corneal epithelial lineage are confined to the b asal cell layer of the limbus, a vascularized outer corneal rim. These slow cycling cells of great proliferative potential maintain the corn eal epithelial mass. Since cell-cell communication plays an important role in development and differentiation, we conducted a comparative ex amination of the expression of two corneal connexin's, Cx43 and Cx50, and the tracer transfer capacity of the limbal and corneal epithelia u sing the scrape loading technique. Cx43 is abundantly expressed in the basal cell layer of the epithelium covering the cornea, but is essent ially absent from the mouse, human, neonatal rabbit, and chicken limba l epithelium. In the adult rabbit the limbal epithelium displays an ov erall weak Cx43 immunoreactivity, but Cx43-free isolated basal cells c an be distinguished. Cx50 is expressed throughout the corneal epitheli um of the three mammalian corneas, but is not detectable in the limbus . Scrape loading experiments in the rabbit yielded results which were consistent with the immunohistological findings; limbal epithelium lac ked tracer (lucifer yellow) transfer capacity, strongly suggesting the absence of functional gap junctions. Altogether, our results demonstr ate the incompetence of stem cells for gap junction-mediated cell-to-c ell communication. This property may reflect the need of these unique cells to maintain a distinct intracellular environment.