Migration of cells in the rat corneal epithelium.

The migration of cells in the rat corneal epithelium was studied using continuous labelling with tritiated thymidine [3H]TdR, during a 24 h period. Most mitoses resulted in 2 new basal cells. Cells leaving the basal cell layer moved vertically to the surface in all areas of the corneal epithelium. The first labelled cells reached the surface 3 days after the first injection of [3H]TdR. No stream of cells from the conjunctiva to the cornea in the limbal areas was observed, and no centripetal migration of epithelial cells in the cornea could be observed. After a cell has lost its attachment to the basement membrane, it is committed to be exfoliated in a few days without undergoing mitosis. Thus the slow centripetal migration of epithelial cells and the exchange of centrally located cells, as indicated by clinical findings and experimental studies, can only be explained by migration of basal cells.