The removal by actinomycin D of the effect of endogenous or exogenous animalizing agents in sea urchin development.

The demonstration by Hörstadiuset al. (1967) that animalizing and vegetalizing agents may be extracted from unfertilized eggs of the sea urchinParacentrotus lividus gave support to the view that a double gradient system of endogenous animalizing and vegetalizing agents regulate the early sea urchin development. The way of action of the endogenous morphogenetic agents may now be approached in a more direct way. A fraction of the egg extract (L. Josefsson) proved to have a pronounced animalizing effect. In sixteen cell stage isolated vegetal half embryos served as reaction systems. Trypsin which acts as an exogenous animalizing agent was tested in parallel way. Actinomycin D which is known as a specific inhibitor of transcription processes removed or almost removed the effect of the animalizing fraction and of trypsin on vegetal half embryos. From this is tentatively inferred that animalizing agents control the transcription of genes specifying the animal differentiation of the embryo.