Recognizes a phosphor-protein of 45kDa, identified as MyoD1. The epitope of this MAb maps between amino acid 180-189 in the C-terminal of mouse MyoD1 protein. It does not cross react with myogenin, Myf5, or Myf6. Antibody to MyoD1 labels the nuclei of myoblasts in developing muscle tissues. MyoD1 is not detected in normal adult tissue, but is highly expressed in the tumor cell nuclei of rhabdomyosarcomas. Occasionally nuclear expression of MyoD1 is seen in ectomesenchymoma and a subset of Wilm s tumors. Weak cytoplasmic staining is observed in several non-muscle tissues, including glandular epithelium and also in rhabdomyosarcomas, neuroblastomas, Ewing s sarcomas and alveolar soft part sarcomas.