Ultrastructure of conjunctival epithelium replacing corneal epithelium.

After corneas of mice had been totally denuded of their epithelium by the application of n-heptanol, the new epithelium which grew over the corneas was studied by electron microscopy at intervals up to 7 months. The purpose was to compare the basal attachment of the new cells, derived from conjunctiva, with that of true corneal epithelial cells growing on the same type of substratum, and studied previously. Goblet cells appeared after 2 weeks amid the squamous type of epithelial cells which had resurfaced the cornea in about 1 week. Goblet cells increased up to at least 6 weeks, but had decreased by 3 months. They persisted, however, for the entire 7 months of the study. Goblet cells had only a small area of contact with the basal lamina, and they had few desmosomes or hemidesmosomes. Basal cells of the squamous type had complex features of their basal attachment quite different from those of normal or repairing corneal epithelial cells studied previously. Flat cytoplasmic extensions of squamous cells underlay most of the goblet cell basal pole which therefore had only a small area on the basal lamina. Numerous filaments inserted into desmosomes and hemidesmosomes of squamous cells, and prominent bundles of these filaments lay just above the basal plasma membrane. They were orientated parallel to the radial axis of the cornea. Closely spaced corrugations of the basal plasma membrane were also orientated in this axis, as well as rows of hemidesmosomes. Even after a period of 7 months, the morphological features of conjunctival cells did not come to resemble those of normal corneal epithelium. The radial arrangement of fibers, hemidesmosome rows, and corrugations is interpreted as a reflection of the continued centripetal migration of the epithelium.