Assessment of osteoblast phenotypic characteristics in hTERT-immortalized MOB and 43KO-MOB mouse cell lines using the key osteogenic marker alkaline phosphatase (ALP) after 12, 24, and 37 population doubling (PD-12, PD-24, PD-37) (A), and the capability to form mineralized extracellular matrix, as determined by von Kossa staining (B). MOBs, 43KO-MOBs, MC3T3-E1 (seeded at 1.5 × 103 cells/cm2), PMOB, and 43KO-PMOB (seeded at 2.0 × 104 cells/cm2) were seeded in six-well plates and stained 2 wk after being plated.