Retention of carboxypropeptides in type-II collagen fibrils in chick embryo chondrocyte cultures.

An antibody reacting with the C-propeptide of chick type-II procollagen was used in an attempt to localize this terminal extension of the procollagen molecule (by immunogold labelling) during early collagen fibrillogenesis in chondrocyte cultures. After 2 days in culture the chondrocytes were surrounded by pericellular type-II collagen, as demonstrated by an indirect immunofluorescence labelling technique. An electron microscopy study of these cultures showed that the collagen fibrils were thin (approximately 15 nm diameter), with a poorly visible cross striation, sometimes enhanced by slight thickenings. The antibody against the C-propeptide of type-II procollagen labelled most of the collagen fibrils, according to a very regular pattern constituting a 60 nm periodicity. After 3 days the label was still present on the pericellular collagen fibrils but disappeared from the collagen fibrils of the extracellular matrix. Our results indicate that the C-propeptide of type-II procollagen is retained in the newly formed fibrils.