Development of the chick columella: immunohistochemical studies with anti-collagen monoclonal antibodies.

Developmentally regulated changes in the extracellular matrices of the columella have been immunohistochemically analyzed with anti-collagen, type-specific monoclonal antibodies. In the 12-day chick embryo, the ossicle is entirely cartilagenous. By using immunohistochemical methods, we found that the 12-day columella contains type II collagen within the cartilagenous matrix and type I collagen in the surrounding perichondrium, but no type X collagen. Previous studies have shown that type X collagen is specific for hypertrophic cartilage (i.e., the site of future marrow cavity formation and ossification). By 16 days, hypertrophic cartilage is evident, type X collagen is present, and ossification has started medially adjacent to the oval window. These results both confirm and extend those of other chick endochondral bones that have been studied. Thus, the columella can serve as a model system for analysis of ossicular development and the associated temporal and spatial changes which occur within its extracellular matrices.