Requisite roles of Runx2 and Cbfb in skeletal development.

Each Runx (runt-related gene) protein exerts a fundamental role in different cell lineages. Runx2 is essential for osteoblast differentiation and plays an important role in chondrocyte maturation. Runx2 determines the lineage of osteoblastic cells from multipotent mesenchymal cells, enhances osteoblast differentiation at an early stage, and inhibits osteoblast differentiation at a late stage. In addition, Runx2 is involved in the production of bone matrix proteins. Further, Runx2 is a positive regulator of chondrocyte maturation and is involved in vascular invasion into the cartilage. Core binding factor beta (Cbfb) is a cotranscription factor which forms a heterodimer with Runx proteins. Cbfb is required for the functions of Runx1 and Runx2. Thus, Runx2/Cbfb heterodimers play essential roles in skeletal development.