Effects of Actinomycin D on Morphogenesis

Abstract

THE possible role in morphogenesis of ribonucleic acids (RNA) produced by the cell nuclei (presumably ‘messenger’ RNA's) has been discussed recently by one of us¹. In short, it was suggested that, in a relatively simple system such as the regenerating unicellular alga Acetabularia, the ‘morphogenetic substances’ of Hämmerling² could be equated to messenger (informational) RNA; however, these substances might as well be proteins, the synthesis of which is controlled by a specific RNA of nuclear origin. The situation is obviously much more complex in the case of embryonic differentiation; we have suggested¹ that, in amphibian eggs, synthesis of messenger RNA does not begin before gastrulation. At that stage of development, the pre-existing polarity gradient in the distribution of ribosomal RNA would become activated by messenger RNA's produced by the nuclei: as a result, RNA and protein synthesis would proceed further along the well-known cephalocaudal and dorsoventral morphogenetic gradients.