Immunohistochemical localization of collagen types I and II in the developing chick cornea and tibia by electron microscopy.

Monoclonal and conventional antibodies against collagen types I and II were used for immunofluorescence and immuno-electron microscopic studies of developing chick corneas (5-day-old embryos to adult) and embryonic limb cartilages. Secondary antibodies were labeled with rhodamine or ferritin. We found that the 5-day primary corneal stroma stains uniformly at the light microscope level with both monoclonal and rabbit antibodies to collagen types I and II. At the electron microscope level, the striated fibrils are stained by these antibodies. After invasion by fibroblasts (7-day-old embryos), type I collagen becomes the predominant collagen within most of the stroma, whereas type II becomes progressively localized in subepithelial (Bowman's membrane) and subendothelial (Descemet's membrane) regions. In the adult the only remaining type II reactivity is in Descemet's membrane. In this structure, both the nodes and strands stain positively for type II. In embryonic cartilage, on other hand, type II collagen is organized as nonstriated fibrils. Thus, during avian corneal development, radical changes occur both in the the types of collagens present and in their distribution. In addition, it seems that the same genetic type of collagen can take several morphologic forms, depending on the environment fibrils as well as in the nodes and strands of Descemet's membrane.