| Differentiation of myogenic cells is regulated by multiple positive and negative regulators. One well characterized family of helix-loop-helix (HLH) proteins known to play an important role in the regulation of muscle cell development includes MyoD, myogenin, Myf-5, Myf-6 (also designated MRF-4 or herculin) and musculin (also designated MyoR). Members of this group of transcription factors form heterodimers with products of a more widely expressed family of bHLH genes, the E family, which consists of at least three distinct genes: E2A, ITF2 and HEB. The E2A gene encodes at lest two different proteins, E12 and E47, as a result of alternative splicing. The myocyte enhancing factor-2 (MEF-2) family of transcription factors includes four splice variants A, B, C and D which encode muscle-specific DNA binding proteins that recognize an A/T rich sequence [CTA (A/T)4 TAG] localized in the control regions of numerous muscle-specific genes. |
