Transcripts for the muscle regulatory gene MyoD1 are expressed during normal skeletal muscle myogenesis and in
rhabdomyosarcomas but not in other tissues or in
soft-tissue sarcomas. Here we report the distribution of MyoD1
protein, determined by reactivity with anti-MyoD1 polyclonal sera in normal tissues,
rhabdomyosarcoma cell lines, and in a variety of pediatric solid
tumors. The distribution of MyoD1
protein was highly restricted in normal tissues and was detected only in fetal skeletal muscle and more faintly in adult skeletal muscle. All six human
rhabdomyosarcoma cell lines analyzed expressed MyoD1
mRNA transcripts as well as immunoreactive
protein. The immunohistochemical expression of MyoD1
protein was then examined in 49 surgical specimens from a variety of pediatric solid
tumors. Each of 16
rhabdomyosarcoma specimens was positive for MyoD1, including four that did not express the intermediate filament
protein desmin. Two of five specimens originally designated
sarcoma type indeterminate (
STI) and two of three specimens originally designated extraosseous
Ewing's sarcoma (EOE) were positive for MyoD1, suggesting commitment to myogenic differentiation. Three of eight Wilms'
tumors, which also expressed
desmin and had clearly evident myogenic elements, also were positive for MyoD1.
Tumors that failed to express MyoD1
protein included
neuroblastoma,
primitive neuroectodermal tumor,
non-Hodgkins lymphoma, embryonal
sarcoma of the liver,
malignant fibrous histiocytoma, malignant
rhabdoid tumor, and
Ewing's sarcoma of the bone. These results indicate that expression of MyoD1
protein is highly restricted in normal human tissues and that expression of this gene product in malignant tissue may be diagnostic for
rhabdomyosarcoma. Furthermore MyoD1 staining may be a valuable adjunct in the classification of pediatric
soft-tissue sarcomas.