Figure 2.

Osteoblast differentiation. Murine osteoblast differentiation is characterized by three stages of growth marked by specific factor expression. During osteoblast proliferation (up to approximately 9 days), osteoblasts produce type I collagen. Osteoblasts enter early differentiation, or extracellular matrix maturation, at approximately 12 days of age, and express the proteins alkaline phosphatase, osteocalcin, and bone sialoprotein. Extracellular matrix mineralization occurs when osteoblasts are approximately 25 days old, where osteoblasts express the proteins osteonectin, osteocalcin, and osteopontin.