A study of the influence of isolated calf spleen RNA on amphibian histogenesis

In the cell-free inductor demonstrated by Niu & Twitty (1953) the effective material was later characterized by Niu (1956) as ribonucleoprotein with the suggestion that the ribonucleic acid (RNA) fraction was the active component. Subsequently Niu (1958 a, b ) reported tissue-specific (thymus-like) induction in amphibian material exposed to calf thymus RNA, though Yamada (1961), using identical procedures, was unable to repeat the results, and Saxén & Toivonen (1962) considered the thymus-like histogenesis in Niu's results to be poor. In the present investigation calf spleen ribonucleic acid was isolated so as to ensure removal of contaminants from the isolate prior to testing for inductive capacity with competent amphibian ectoderm and embryos. Sedimentation nalysis with the ultracentrifuge indicated that the isolated spleen ribosomal RNA was undegraded when introduced into the culture medium. In a limited series of test cases neither embryos nor ectodermal isolates of Xenopus laevis demonstrated any tissue-specific inductive response (i.e. erythropoiesis), though a general enhancement of epithelial development was obvious.