To decipher the developmental basis of expression of Msx-1 gene, we introduced DNA constructs in which luciferase or beta-galactosidase (lacZ) reporter genes were driven by the potential cis-regulatory sequences of Msx-1 into NIH 3T3 and C2C12 cells, and in transgenic mice. Analysis of expression of the reporter genes revealed a glimpse into the complexity of the regulatory elements of Msx-1 promoter which activate it in vitro in cultured cells and during embryogenesis.