An ultrastructural study of rabbit ocular surface transdifferentiation.

When debridement of the rabbit cornea is followed by re-epithelialization from the conjunctiva, a process of transdifferentiation of the endothelium occurs. Goblet cells appear peripherally 1 week after healing of the epithelial defect, are widespread at 2 weeks, and disappear centrally at 3 to 4 weeks. Six weeks after closure of the defect, the epithelium has reverted to the customary corneal appearance. The morphology of the regenerating epithelium was studied by light, transmission and scanning electron microscopy. The precursor cells for the goblet cells were identified in stage 1, before PAS-positive cells were present, as pairs of cells with dark cytoplasm and prominent Golgi. Subsequently, goblet cells were present in pairs, indicating that goblet cells are derived from non-goblet epithelial cells, and that they do not simply migrate onto the cornea. At the time of transdifferentiation, loss of goblet cells was shown to occur both by desquamation from the surface and by in situ cell death.