Muscle cell differentiation was analysed by two-dimensional gel electrophoresis of newly synthesized
proteins compared in two parallel systems: in mouse
teratocarcinoma-derived
tumors that became restricted in their developmental potential to the formation of muscle-like cells and in developing limbs of the early mouse fetus. Muscle cell differentiation in
teratocarcinomas was found to be reflected by both a marked decrease in the rate of synthesis of about 12% (119
proteins) of the resolved
polypeptides and a pronounced increase in the synthesis of another large set of
proteins (83
proteins). The majority of the newly acquired
proteins (46
proteins) were also detected in fetal brain and muscle tissue. These
proteins are considered to be those which accompany differentiation in general, regardless of cell type, as e.g. ubiquitously occurring structural
proteins. Their expression in the muscle cells of the
tumors may reflect the normal aspect of this particular differentiation pathway. Five
polypeptides were found to appear specifically in both myogenic
tumors and developing limbs, but not during brain formation and were tentatively termed muscle-specific
proteins (MSP). The identification of differentiation-related
proteins in muscle development will allow us to analyse differentiation in early development in molecular terms.