Myogenic Differentiation 1 (MyoD1) belongs to a family of myogenic helix-loop-helix transcription factors, and, when combined with myogenin, plays a key role in the myogenic or muscle differentiation pathway. MyoD1 is expressed in myoblasts and in activated satellite cells, but not in normal mature skeletal muscle or in quiescent satellite cells. . It regulates muscle cell differentiation by inducing cell cycle arrest, a prerequisite for myogenic initiation. The protein is also involved in muscle regeneration. Anti-MyoD1 is therefore used to identify cells that are committed to myogenesis. Anti-MyoD1 is also utilized as a biomarker for rhabdomyosarcomas, a malignant soft tissue neoplasm, often as part of a panel also including Anti-Myogenin and Anti-Desmin. It is a sensitive and specific marker for myogenic differentiation.