The effect of thyroxine on ribonucleic acid synthesis by premetamorphic tadpole liver cell suspensions.

Suspensions of tadpole liver cells have been developed as a model to further understanding of the biochemical differentiation of this tissue during thyroxine-induced metamorphosis. The cell population is homogeneous and stable; no cell division or DNA synthesis occurs in these isolated cells. RNA synthesis in cell suspensions is stimulated by thyroxine and triiodothyronine. The optimum concentration of both thyroxine and triiodothyronine for stimulation of RNA synthesis is about lo-‘M. Rapidly labeled RNA isolated from thyroxine-treated and nontreated cell suspensions sediments in the region between 4 and 10 S. The base composition of RNA synthesized by liver cells treated in vifro with thyroxine differs significantly from that of untreated liver cells and from bulk tadpole liver RNA. The ratio of cytosine plus guanine to total bases of RNA from thyroxine-treated cells is similar to that of DNA from this species. Neither thyroxine nor triiodothyronine had any effect on the incorporation of amino acids into protein. Frog serum stimulates RNA and protein synthesis. Rana cafesbeiana serum causes the aggregation of isolated liver cells.