Direct contact at the epithelial-mesenchymal interface during the early development of the chicken ciliary epithelium

Abstract

Ciliary epithelium from 5–21-day-old chicken embryos was studied by scanning and electron microscopy. During this stage of development an interaction at the epithelial-mesenchymal interface was observed. Close junctions between epithelial and mesenchymal cells were restricted to the eighth day of incubation. This direct contact was formed by epithelial cell extensions which pass through gaps in their basement membrane to contact mesenchymal cells. In these zones of contact the intercellular space between both structures is less than 110 Å. Condensation of electron-dense material was often seen over a short distance, especially on the inner surface of the mesenchymal cell membranes; membrane fusion was not observed. At the epithelial-mesenchymal interface extracellular collagen fibrils were interposed. The possible role of close junctions between epithelium and mesenchyme and the role of collagen fibrils for the differentiation of the ciliary epithelium are discussed.