Integrins in Slow‐Cycling Corneal Epithelial Cells at the Limbus in the Mouse

Adult corneal epithelial stem cells (CESCs) have been shown to reside at the periphery of the cornea at a site called the corneoscleral junction or limbus. Although studies have shown that these cells are slow cycling, their molecular characteristics are not well understood. Using a whole‐mount procedure, we show that whereas α 9 ‐integrin is present in a subset of the basal cells at the corneal limbus and absent in the central cornea, β 1 ‐, β 4 ‐, α 3 ‐, and α 6 ‐integrins are more highly expressed overall in central corneal basal cells. To characterize CESCs based on their slow‐cycling nature, we simultaneously evaluated 5‐bromo‐2‐deoxyuridine (BrdU) label‐retaining cells (LRCs) and integrin expression (α 9 , β 1 , and β 4 ) in a total of 1,889 cells at the limbus of adult mice that had been injected as neonates with BrdU. Whereas the LRCs were usually observed adjacent to α 9 ‐integrin‐positive cells, most LRCs were α 9 ‐integrin–negative and expressed high levels of β 1 ‐ and β 4 ‐integrin. In addition, we observed more BrdU‐positive LRCs at the superior and inferior quadrants of adult mouse corneas than at the nasal and temporal quadrants, and determined that 0.94 to 3.6% of the limbal basal cells were slow cycling. We conclude from these data that the slow‐cycling LRCs in the adult mouse cornea are enriched in cells that express high levels of β 1 ‐ and β 4 ‐integrin and little α 9 ‐integrin.