Bone matrix deposition of T1, a homologue of interleukin 1 receptors

The mouse T1 glycoprotein is a secreted molecule of the immunoglobulin superfamily with significant homology to interleukin 1 receptors. It is expressed during bone development, and the extracellular diffusible gene product is found associated with newly formed bone but not cartilage matrix. During osteogenic differentiation of mandibular condyles of newborn mice in vitro, T1 gene expression is induced shortly after cultivation and is observed throughout the differentiation process. The temporal expression pattern of the gene is an mandibular condyles indicates that T1 expression is an early marker of osteogenic differentiation. This view is substantiated by the analysis of T1 gene regulation in continuous osteogenic cell lines. Both in differentiating osteoblast-like KM-1K cells derived from mandibular condyles and in MC3T3 cells, T1 gene activity is preferentially associated with early differentiation stages. In mandibular condyles, the secreted extracellular T1 protein is deposited into newly formed osteoid but not into cartilage matrix. This novel bone matrix protein may locally modulate the availability of its ligand.