An inverse relation between the rate of cell division and RNA synthesis per cell in developing frog embryos

Previous work has shown that endoderm cells synthesize more RNA per cell, including nuclear d-RNA, than do dorsal ectoderm-mesoderm cells (Flickinger, Miyagi, Moser & Rollins, 1967; Woodland & Gurdon, 1968). Both groups found lower levels of DNA synthesis in endoderm cells compared to dorsal ectoderm-mesoderm cells. It has also been found that in developing frog embryos both LiCl and cytosine arabinoside inhibit DNA synthesis and also inhibit RNA synthesis. Since RNA synthesis is inhibited less than DNA synthesis, the levels of RNA synthesis relative to total DNA increase (Flickinger, Miyagi, Moser & Rollins, 1967). A number of investigators have demonstrated that LiCl can cause isolated amphibian gastrula ectoderm to form endoderm and mesoderm (Barth & Barth, 1962; Gebhardt & Nieuwkoop, 1964; Masui, 1966; Ogi, 1961). Such compounds as NaHCO3 (Barth & Barth, 1963) and NaCl (Barth, 1966) can induce isolated frog gastrula ectoderm to form neural tissue.