We analyzed actin expression in two human
rhabdomyosarcomas as well as in three
rhabdomyosarcomas induced in rats by the injection of
nickel sulfide. All five
tumors exhibited appreciable amounts of the sarcomeric
alpha-actin types, in line with their myogenic differentiation. The level of these
actins was particularly high in the rat
tumors, which according to morphological criteria, all showed a higher degree of differentiation than the human
tumors. Interestingly, in both human
tumors and in two of the three rat
tumors, the level of the cardiac
alpha-actin type was significantly higher than that of adult skeletal muscle
alpha-actin. Taken together with the results of recent reports indicating that the cardiac
alpha-actin type is a marker of embryonic and fetal skeletal muscle, our findings indicate that
rhabdomyosarcomas express the embryonic sarcomeric actin
isoform.