Tenascin is associated with articular cartilage development

The roles of tenascin in cartilage development and function remain unclear. Based on the observation that tenascin is particularly abundant at the epiphyseal extremities of developing cartilaginous models of long bones in chick and mouse embryo, we tested the hypothesis that tenascin is involved in articular cartilage development. Immunofluorescence analysis revealed that tenascin was first localized in the cell condensation region of Day 4 chick embryo limb buds, where the cartilaginous models form. With further development, tenascin gene expression became indeed restricted to the articular cap of the models. Tenascin persisted in the articular cartilage of postnatal chickens but appeared to decrease with age. The protein was also abundant in embryonic and adult tracheal cartilage rings which, like articular cartilage, persist throughout postnatal life. Similar patterns of tenascin expression were seen in mouse. Using monoclonal antibodies to avian tenascin variants, we found that the bulk of articular cartilage contained the shortest tenascin variant (Tn190), whereas the largest variant (Tn230) was present in tissues associated or interacting with articular cartilage (ligaments and meniscus). The protein and its mRNA, however, were undetectable in growth plate cartilage undergoing maturation and endochondral ossification. This inverse correlation between chondrocyte maturation and tenascin production was corroborated by the finding that tenascin gene expression decreased markedly during maturation of chondrocytes in culture and during formation of a secondary ossification center within the articular cap in vivo. Thus, tenascin is intimately associated with the development of articular cartilage and other permanent cartilages whereas absence or reduced amounts of this matrix protein characterize transient cartilages which undergo maturation and are replaced by bone.