The changing inhibition of early differentiation and general development in the chick embryo by 2-ethyl-5-methyl-benzimidazole and chloramphenicol.

STUDIES conducted during the past 10 to 15 years primarily in amphibian and chick embryos have led to a controversy over the identity of substances principally responsible for induction and early differentiation. That ribonucleoproteins are most directly involved is widely accepted. However, the question of which is most important ribonucleic acid (RNA) or protein has been the major point of disagreement. Brachet (1950) first suggested that RNA plays the primary role in induction and early differentiation. Several investigators studying the inductive properties of denatured ribonucleoprotein preparations from mammalian organs on amphibian gastrula ectoderm have concluded that protein is of greater importance than RNA (reviews, Barth, 1957; Yamada, 1958). Work with non-denatured thymus preparations led Niu (1958) to report that protein plays a role in differentiation but that RNA is the causal agent. Most studies on induction have used non-embryonic materials as inductors. The inductive actions produced under the experimental conditions are therefore not necessarily the same processes as occur in the normal embryo. Another approach to the problem of differentiation is that of altering morphogenesis by interrupting specific biochemical processes in the early embryo through the use of metabolic antagonists, i.e. by chemical teratogenesis. Embryologists generally consider that both the teratogen and the stage of embryonic development at the time a teratogen is applied determine the teratogenic response. It should be possible to gain knowledge pertaining to the biochemical processes underlying early differentiation by determining the relationships among the three variables: the teratogen, the stage of embryonic development, and the teratogenic response. Therefore, the roles of RNA and protein synthesis in induction and differentiation