[Properties of polyribosomal complexes of loach embryonic cell cytoplasm]

The translation-active complexes of the extranuclear region of cytoplasm of developing loach (Misgurnus fossilis) embryos were studied. The amount of ribosomes involved in polyribosomal complexes was shown to increase 6-fold from the blastula stage to organogenesis, making up only a small (3% and 18%, respectively) part of the total pool of cytoplasmic ribosomes. Free polyribosomes make up the bulk (up to 95%) of the total cytoplasmic polyribosomal pool at early stages of development (blastula, gastrula) and about 50% at late stages (organogenesis). The membrane-bound polyribosomes appear in early gastrulation; their content reaches its maximum (40-45%) in organogenesis. The newly formed RNAs liberated from the nucleus into the extranuclear space of the cytoplasm in the course of ontogenesis are incorporated into the polyribosomes (predominantly membrane-bound ones) not before the gastrulation starts. The proportion of these poly(A)-enriched mRNAs in the polyribosomes does not exceed 10% of the total amount of newly synthesized cytoplasmic RNAs at this stage. A population of light polyribosomes capable to synthesize histones was detected in free polyribosomes, which do not practically contain the newly formed RNAs. The data obtained are discussed in terms of the literary data on the type of RNA and protein synthesis in early ontogenesis.