BONE-MATRIX DEPOSITION OF T1, A HOMOLOG 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 carti lage 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. Th e temporal expression pattern of the gene in mandibular condyles indic ates that T1 expression is an early marker of osteogenic differentiati on. This view is substantiated by the analysis of T1 gene regulation i n 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 differentiati on stages. In mandibular condyles, the secreted extracellular T1 prote in is deposited into newly formed osteoid but not into cartilage matri x. This novel bone matrix protein may locally modulate the availabilit y of its ligand.