Changes in Protein Synthesis in the Morphogenesis of Fundulus heteroclitus

IN the deuterostomes, RNA previously synthesized in the oocyte or on maternal genetic templates is required for development of the embryo through the blastula 1,2 . In sea urchin 3 , amphibian 4,5 and fish 6–8 zygotes early and continuous exposure to actinomycin D resulted in blastula arrest. Removal of the drug before the third cleavage in the sea urchin allowed normal development through gastrulation 9 although in the fish 6 , in spite of a similar removal, gastrulation is abnormal and surviving embryos are defective. Further development awaits a switch to the immediacy of nucleus-directed RNA synthesis. Information necessary for gastrulation is synthesized during cleavage stages and appears to be stored before it is utilized 10,11 .