To further examine this phenotype in a cell autonomous system, we chose the embryonic mesenchymal multipotential progenitor cells C3H10T1/2. The addition of BMP-2 induced osteoblast differentiation, as evidenced by an approximately 400-fold increase in expression of the osteocalcin (OCN) gene [51]. Populations of C3H10T1/2 cells stably transfected with either pSuper-retro (control) and pSuper-retro harboring a short hairpin against Sam68 (Sam68sh) were selected with puromycin. The expression of Sam68 was reduced by approximately 80% as evidenced by immunoblot analyses using β-actin as a loading control (Figure 8A). Osteoblast differentiation was induced in cultures expressing pSuper-retro or pSuper-retro Sam68sh by addition of BMP-2 to the culture medium. . The expression of OCN and β-actin mRNAs was examined by semiquantitative RT-PCR and the Sam68sh-expressing cells displayed a more pronounced osteoblast phenotype compared with control cells, as assessed by the expression of OCN (Figure 8B).