Expression and localization of extracellular matrix proteins in rat skeletal development

Abstract: Several novel matrix molecules of cartilage and bone have recently been identified and characterized. Studies of the maturation of the femoral head give clues as to the function of the novel matrix proteins. We have studied the expression and localization of two cartilage proteins: COMP, chondroadherin (CHAD), and two bone proteins: BSP and osteoadheirn (OSAD). COMP was localized throughout cartilage and was expressed by chondrocytes with high levels in proliferative chondrocytes and low in hypertrophic chondrocytes. An age dependent shift in localization from territorial matrix to interterritorial matrix was seen during maturation of the articular cartilage. BSP was localized to trabecular bone and lower hypertrophic chondrocytes, and it was expressed by osteoblasts. COMP and BSP where examined during cartilage and bone formation by subcutaneous implantation of demineralized bone powder. CHAD cDNA of rat has been determined. Expression of mRNA for CHAD was not only found in femoral head, rib cartilage but also in bone, tendon and bone marrow tissues by RT-PCR. In the femoral head the protein was localized to cartilage by immunostaining and a strong increase in intensity of staining was seen in proliferative cells of growth plate in mature femoral head. Expression of mRNA for CHAD was found mainly in proliferactive cells. The amount of chondroadherin in the matrix was substantially increased with rat growth. Structure of OSAD of bovine, a novel cell binding, has been determined by cDNA sequencing. OSAD has been shown to belong to leucine-rich repeat protein family. The protein was localized to trabecular bone. Partial rat OSAD cDNA has also been sequenced. Expression of mRNA for OSAD was found in bone and limited other tissues by RT-PCR. In situ hybridization showed that the mRNA for OSAD was highly expressed by osteoblasts close to interface between cartilage and bone.