Type X collagen is colocalized with a proteoglycan epitope to form distinct morphological structures in bovine growth cartilage.

Using antibodies raised against type X collagen, isolated from deer antler, we have immunolocalized type X collagen in growth plate and epiphyseal cartilage from fetal and ambulatory calves. In ambulatory calf growth plate, type X collagen was demonstrated to be present in longitudinal septa that extend from the resting zone into the underlying trabecular bone. The much more restricted distribution of type X collagen seen in fetal growth plate, both here and previously, suggested that prominent localization of type X collagen to the longitudinal septa was stimulated by weight bearing. The location of type X collagen has been compared with that of an epitope (7D4), composed of specific sulfation patterns in chondroitin sulfate of some aggrecan molecules. Colocalization of type X collagen with the 7D4 epitope in longitudinal septa of growth plates from ambulatory calves suggested these molecules contribute to the formation and function of longitudinal septa. Immunolocalization of type X collagen and 7D4 in calf epiphyseal cartilage demonstrated colocalization at an interface that appears to represent the junction of articular cartilage and cartilage associated with formation of the secondary ossification center. Immunolocalization of type X collagen and the 7D4 proteoglycan epitope in these structures suggested that type X collagen and the 7D4 epitope form structures with important mechanical roles and capacity to influence the morphology of associated bony structures.