Mouse teratocarcinoma and embryonic development. Two-dimensional protein patterns in muscle differentiation.

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.