IMMUNOLOCALIZATION OF OSTEONECTIN IN AVIAN TIBIAL DYSCHONDROPLASTIC CARTILAGE

Osteonectin is an acidic calcium-binding protein found in cartilage, b one matrix, vascular endothelium, and areas of tissue repair. Using im munocytochemistry, osteonectin has been localized in all zones of the normal avian epiphyseal growth plate with notably high amounts in the hypertrophic zone. In the proximal portion of this zone the staining w as intracellular, while in the distal calcifying portion of the hypert rophic zone staining was both intracellular and extracellular. Osteone ctin was also detected in the growth plate associated with lesions of chickens with tibial dyschondroplasia (TD). Intense intracellular stai ning was observed in hypertrophic chondrocytes proximal to the lesion; staining was markedly diminished in the TD lesion; extracellular matr ix was devoid of staining. Staining intensity was high along the perip heral edges of the lesion that were undergoing vascularization and res orption. This was the only area in the dysplastic cartilage where stai ning was observed in the extracellular matrix as well as intracellular ly. Similar patterns were viewed in all TD lesions examined, whether t hey were spontaneous or induced by dietary treatments or genetic selec tion. (C) 1996 Wiley-Liss, Inc.