TRANSFORMING GROWTH FACTOR-BETA-1, FACTOR-BETA-2 AND FACTOR-BETA-3 IN CARTILAGE AND BONE-CELLS DURING ENDOCHONDRAL OSSIFICATION IN THE CHICK

The localization of TGF-beta-1, -beta-2 and -beta-3 was studied in the growth plate, epiphysis and metaphysis of the tibiotarsus of three-week-old chicks. The different TGF-beta-isoforms were localized to hypertrophic chondrocytes, chondroclasts, osteoblasts and osteoclasts using immunohistochemical staining analysis with specific TGF-beta-antibodies. TGF-beta-s in osteoclasts and chondroclasts were restricted to those cells located on the respective matrices. TGF-beta-3 localization was mainly cytoplasmic in the transitional (early hypertrophic) chondrocytes, but nuclear staining was also detected in some proliferating chondrocytes. The cell-specific localization of these TGF-beta-isoforms supports the hypothesis that TGF-beta has a role in the coupling of new bone formation to bone and cartilage matrix resorption during osteochondral development and suggests that TGF-beta may be a marker of chondrocyte differentiation. TGF-beta-localization preceded a marked increase in type II collagen mRNA expression in transitional chondrocytes, suggesting a role for TGF-beta in the induction of synthesis of extracellular matrix.