Fig. 4. Transfection with MyoD expression vector partially rescues the osteogenic response of MyoD^-/- cells to BMP-7. The phenotype of MyoD^-/- cells, stably transfected with either a MyoD-expression vector or its empty vector, was compared to wild-type cells after a 3-day incubation with BMP-7 (400 ng/ml). Cultures were double-stained for MHC expression (brown/black) and ALP activity (blue). Wild-type cells (A), MyoD^-/- cells (B), MyoD^-/- cells transfected with PGK-puro (C) or pEMSV-MyoD/PGK-puro vectors (D). Immunostaining analysis of the transfected cultures shows that only the MyoD transfected cultures are positive for MyoD expression (compare insets in C and D). Scale bar, 100 µm.