Uptake and utilization of mRNA by myogenic cells in culture

Primary chick myoblast cultures demonstrate the ability to take up exogenously supplied polyadenylated RNA and express the encoded information in a specific manner. This expression is shown to exhibit tissue specificity. Analysis of creatine kinase activity monitored at various times of incubation in the presence of either polyadenylated or nonpolyadenylated RNA indicates that only the poly(A)+ mRNA is capable of being actively translated. Radioactively labled poly(A)+ mRNA is taken up by the cell cultures in a time-dependent manner and subsequently shown to be associated with polysomes. This association with polysomes does not occur in the presence of puromycin and is unaffected by actinomycin D. Thus, nonspecific interaction with polysomes and induction of new RNA synthesis are ruled out and the association of the exogenously supplied poly(A)+ mRNA with polysomes is indicative of its translation in the recipient cells. When heterologous mRNA (globin) is supplied to the myoblasts, it is also taken up and properly translated. In addition, exogenously supplied myosin heavy chain mRNA is found associated with polysomes consisting of 4-10 ribosomes in myoblast cell cultures while in myotubes it is associated with very large polysomes, thus reflecting the different translational efficiencies that this message exhibits at two very different stages of myogenesis. The results indicate that muscle cell cultures can serve as an in vitro system to study translational controls and their roles in development.