Osteoblasts are derived from mesenchymal stem cells of the bone marrow cavity and are responsible for the formation and mineralization of new bone tissue known as osteoid. As osteoblasts become encased in mineralized osteoid, they remain isolated in lacunae and their nomenclature changes to osteocytes. Osteoblast differentiation can be induced in vitro from mesenchymal stem-cell cultures in the presence of factors such as ascorbic acid, dexamethasone, β-glycerophosphate, and bone morphogenetic protein (BMP). Mature osteoblasts can be defined phenotypically by positive staining for alkaline phosphatase (ALP) and von Kossa staining, signifying calcium deposits in the extracellular matrix. On a molecular level, terminally differentiated osteoblasts express the transcription factor Cbfa1/Runx2 and an array of other markers including osteocalcin, osteonectin, bone sialoprotein, osteopontin, and type-I collagen.