Molecular structure and tissue distribution of matrilin-3, a filament-forming extracellular matrix protein expressed during skeletal development

Matrilin-3 is a recently identified member of the superfamily of proteins c ontaining von Willebrand factor Ih-like domains and is able to form hetero- oligomers with matrilin-1 (cartilage matrix protein) via a C-terminal coile d coil domain. Full-length matrilin-3 and a fragment lacking the assembly d omain were expressed in 293-EBNA cells, purified, and subjected to biochemi cal characterization. Recombinantly expressed full-length matrilin-3 occurs as monomers, dimers, trimers, and tetramers, as detected by electron micro scopy and SDS-polyacrylamide gel electrophoresis, whereas matrilin-3, purif ied from fetal calf cartilage, forms homotetramers as well as hetero-oligom ers of variable stoichiometry with matrilin-1, In the matrix formed by cult ured chondrosarcoma cells, matrilin-3 is found in a filamentous, collagen-d ependent network connecting cells and in a collagen-independent pericellula r network. Affinity-purified antibodies detect matrilin-3 expression in a v ariety of mouse cartilaginous tissues, such as sternum, articular, and epip hyseal cartilage, and in the cartilage anlage of developing bones. It is fo und both inside the lacunae and in the interterritorial matrix of the resti ng, proliferating, hypertrophic, and calcified cartilage zones, whereas the expression is lower in the superficial articular cartilage. In trachea and in costal cartilage of adult mice, an expression was seen in the perichond rium. Furthermore, matrilin-3 is found in bone, and its expression is, ther efore, not restricted to chondroblasts and chondrocytes.