Bone, muscle, fat, and cartilage are differentiated adult tissues derived from embryonic mesoderm. Under the control of specific molecular and cellular signals, mesenchymal stem cells differentiate into one of these mature tissues. The involvement of the master genes myoD, myogenin, and myf-5 in muscle differentiation is well understood and represents a model for the regulation of mesodermal differentiation (1). At the present, the understanding of similar master signals involved in osteoblast, adipocyte, and chondroblast differentiation remains incomplete.