Abstract
Autoradiographic investigation of differentiating thigh muscle tissue cultures showed that after brief exposures to radioactive uridine or cytosine, the amount of labeling of nuclei within muscle fibers was significantly lower than the labeling of nuclei within the mononucleated cells. The decrease in the rate of labeling which occurred at the onset of fusion of the myoblast into multinucleated fibers cannot be ascribed to greater absorption of the β rays by the cytoplasm of differentiated cells nor is it due to lack of penetration of the labeled precursor into the cells. The difference in the incorporation of RNA precursors also does not seem to arise from differences in the mitotic activity of the various cell types, since inhibition of mitosis by X-irradiation did not abolish the differential rate of incorporation of uridine into RNA. The incorporation of 3H-leucine, unlike that of radioactive uridine, does not seem to decrease following cell fusion. Application of actinomycin D resulted in a higher inhibition of amino acid incorporation into mononucleated cells compared with that into multinucleated fibers. The significance of these results in relation to the possible formation of a stable type of RNA during differentiation is discussed.
Published Version
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