Upstream region of the myogenin gene confers transcriptional activation in muscle cell lineages during mouse embryogenesis.

Myogenin, one of the MyoD-related factors containing basic-helix-loop-helix motifs, is transcriptionally activated in skeletal muscle lineages in somites and limb buds during embryogenesis. In an attempt to understand regulatory mechanisms which govern transcriptional activation of the myogenin gene, transgenic mice bearing the lacZ gene driven by the upstream region of the myogenin gene were generated. Stereoscopic visualization of LacZ-positive cells of these transgenic mouse embryos revealed that the upstream region of the myogenin gene conferred its transcriptional activation in cells of the skeletal muscle lineages in somites, limb buds, and visceral arches. Moreover, transient LacZ expression in newly formed somites in addition to its strong activation in myotomal regions of mature somites with a rostro-caudal gradient raised the possibility that myogenin is transcriptionally activated in immature somites before myotome formation.