Abstract
Summary
Poly(A)-attached RNA (mRNA) was isolated from chicken and calf hearts. Both mRNAs were found to induce the development of explanted postnodal pieces (PNP) of stage 4 chick blastoderm into beating tubes and/or tissues. Heart formation is specific and the frequency was found to depend entirely upon the concentration of mRNA used. In contrast, the concentration had no influence on other tissue formation e.g., neural tube, tubules, myoblasts, and/or notochord.
The uptake of heart [3H]RNA by PNP cells was analyzed using high-resolution autoradiography. Silver grains were localized more in nucleus than in cytoplasm. The effect of heart mRNA on PNP was sensitive to actinomycin D and bromodeoxyuridine. It appears, therefore, that exogenous mRNA plays an important role in nuclear function. This RNA may affect the nuclei of intact cells in two ways: (1) as a derepressor, and (2) as a primer of new DNA synthesis. These alternatives were tested experimentally using the isozyme, lactate dehydrogenase, as marker. Homogenates of the chicken and calf heart mRNA-induced beating tissues were subjected to gel electrophoresis. Both gels had one band (isozyme IV) that was typical of the chicken heart. Accordingly, the mRNA activates but does not transform the genome of embryonic chick tissue.
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