FIG. 2.

Role and delicate regulation of Runx2 during osteoblast differentiation. Runx2 is essential for skeletal development. In osteoblast differentiation, Runx2 expression is detected in preosteoblasts expressing type I collagen weakly and is upregulated in immature osteoblasts expressing osteopontin. However, Runx2 expression is downregulated in mature osteoblasts expressing osteocalcin (OC). As the osteoblast transitions to an osteocyte expressing secreted proteins CD44, DMP1, and MEPE, alkaline phosphatase is reduced, whereas OC is elevated. The expression and transcriptional activity of Runx2 are tightly regulated by multiple proteins during osteoblast differentiation.