Fig. 1. Msx1 inhibits differentiation of multiple mesenchymal progenitor cell types. (A) C2C12 cells (a-d) or 10T1/2 cells (e-h) were infected with a control mammalian retrovirus (Vector) or retroviruses expressing Msx1 or Msx1A. Infected cells were grown under normal culture conditions (undifferentiated; a,e) or conditions that promote differentiation (differentiated; b-d,f-h) to myoctyes (b-d) or adipocytes (f-h). (B) Primary cultures of chicken limb chondrogenic cells (a-c) or calvarial osteogenic cells (e-g) were infected with a control avian retrovirus (Vector) or those expressing Msx1 or Msx1A. Differentiation is visualized by Alcian Blue staining (a-c) or silver staining (e-g). TMC23 chondrocytes (d) or BMP2T3 osteoblasts (h) were infected with a control mammalian retrovirus (Vector) or those expressing Msx1 or Msx1A followed by growth in conditions that promote differentiation. Alkaline phosphatase activity was measured from cell lysates; error bars show standard deviations of assays carried out in triplicate. (A,B) Representative data from experiments repeated a minimum of three times. Scale bars: 0.1 mm in A; 1 mm in B.