MyoD is a protein that plays a major role in regulating muscle differentiation. MyoD, which was discovered in the laboratory of Harold M. Weintraub, belongs to a family of proteins known as myogenic regulatory factors (MRFs). These bHLH (basic helix loop helix) transcription factors act sequentially in myogenic differentiation. MRF family members include MyoD, Myf5, myogenin, and MRF4 (Myf6).MyoD is one of the earliest markers of myogenic commitment.