MyoD1, one of the MyoD family of myogenic helix-loop-helix transcription factors, combined with myogenin, plays a role in coordinating the myogenic differentiation pathway from the determination of mesodermal precursors into myoblasts, the differentiation of myoblasts into myotubes, and finally the maturation of myotubes into skeletal myofibers. Normal mature skeletal muscle does not express MyoD1 protein. MyoD1 is expressed in myoblasts before differentiation while myogenin has post-differentiation functions.