Intercellular junctions in the developing rat corneal endothelium.

The surface events which occur during the morphogenesis of the corneal endothelium were studied in the rat with special attention to intercellular contacts, using scanning and transmission electron microscopy, and freeze-fracture technique. Confluency was reached at the 16th-17th day of fetal development. As soon as adjacent cells make contact, marginal interdigitated finger-like processes developed and apical cell junctions appeared, namely tight and gap junctions. Tight junction networks progressively developed, girdling the apical side of lateral membranes, nevertheless, they remained very irregular in their apicobasal thicknesses. At every stage studied, neutralized lanthanum used as an ultrastructural tracer was seen filling the intercellular clefts and junction domains. Hence, the apical junctions do not constitute an impermeable barrier to this tracer in the developing corneal endothelium.