Hemidesmosome formation in vitro.

Intact, viable sheets of adult rabbit corneal epithelium, 9 mm in diameter, were prepared by the Dispase II method (Gipson, I. K., and S. M. Grill, 1982, Invest. Ophthalmol. Vis. Sci. 23:269-273). The sheets, freed of the basal lamina, retained their desmosomes and stratified epithelial characteristics, but lacked hemidesmosomes (HD). Epithelial sheets were placed on fresh segments of corneal stroma with denuded basal laminae and incubated in serum-free media for 1, 3, 6, 18, or 24 h. Tissue was processed for electron microscopy, and the number of HD/micron membrane, the number of HDs with anchoring fibrils directly across the lamina densa from them, and the number of anchoring fibrils not associated with HDs were counted. After 6 h in culture, the number of newly formed HD was 82% of controls (normal rabbit corneas), and by 24 h the number had reached 95% of controls. At all time periods studied, 80-86% of HDs had anchoring fibrils directly across the lamina densa from them. Anchoring fibrils not associated with HDs decreased with culture time. These data indicate that the sites where anchoring fibrils insert into the lamina densa may be nucleation sites for new HD formation. Corneal epithelial sheets placed on two other ocular basal laminae, Descemet's membrane and lens capsule, had not formed HDs after 24 h in culture. These two laminae do not have anchoring fibrils associated with them. Rabbit epithelial sheets placed on the denuded epithelial basal lamina of rat and human corneas formed new HDs. Thus, at least in these mammalian species, HD formation may involve some of the same molecular components.