It is shown that in loach embryos the incorporation of precursors into protein takes place in the blastoderm cells only. The change of the rate of incorporation of labelled amino acids into protein of the blastoderm separated from the yolk at successive developmental stages reflects the changes in the level of protein synthesis in intact embryos of the same developmental stages. Typical periodic changes of the intensity of protein synthesis in early embryo-genesis of the loach are detected: low incorporation of amino acids at blastula stages is followed by an increase of synthesis during gastrulation and by a decrease with the onset of organogenesis.

To study the genetic control over protein synthesis at various developmental stages of loach and sea-urchin embryos the effects of ionizing radiation and long-term treatment with actinomycin D have been examined. X-Irradiation doses produce an insignificant direct effect on protein synthesis, while radiation damage of the nuclear apparatus results in a gradual but ever increasing inhibition of protein synthesis. The inhibition of RNA synthesis with actinomycin or ionizing radiation damage of the nuclei produce essentially the same effect on the intensity of protein synthesis. Protein synthesis in androgenetic haploid hybrid embryos (loach ♀ × goldfish ♂) and in loach androgenetic haploid embryos after producing a partial elimination of chromosomes does not differ from ‘enucleated’ loach embryos completely deprived of chromosomes. These data suggest that high-polymeric RNA formed after the elimination of some chromsomes is unable to provide a normal level of protein synthesis.

Protein synthesis is not controlled by the nuclei up to the stages of early blastula (sea urchin) and of late blastula (loach), being evidently programmed in oogenesis. To provide a rapid activation of protein synthesis in the course of gastrulation in the loach the function of the nuclei has to be realized during mid-blastula stages. An increase of the rate of the incorporation of amino acids at the stages of mesenchyme blastula in the sea urchin depends on the synthesis of RNA at the early blastula. At the same time protein synthesis during gastrulation in the loach and at mesenchyme blastula in the sea urchin is much less dependent on the simultaneous RNA synthesis. Protein synthesis at these stages seems to be provided by the long-living templates and controlled by non-gene mechanisms of the regulation of translation.

Thus early embryonic differentiation in the loach and sea-urchin development is related to the activation of protein synthesis. The latter is provided by the preceding morphogenetic nuclear function, which makes protein synthesis relatively independent of simultaneous synthesis of templates that ensures subsequent development stages.

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