[The dynamics of the specific activity of newly synthesized RNA during loach embryo development]

The transport of the stable form of newly synthesized RNA from the nucleus to the cytoplasm has been studied in the loach (Misgurnus fossilis) development. Following the pulse labelling with 3H-uridine, the embryos were cultivated in the medium with non-labelled uridine and actinomycin D. The cell homogenate was fractionated and the specific activity of nuclear and cytoplasmic RNAs was determined. It was shown that a great part of newly synthesized RNA degraded within the nucleus and its insignificant part was preserved in the nucleus for several hours. The exit of stable RNA in the cytoplasm depends on the developmental stage. This part of RNA was found to stay in the nucleus at the stages of early--midblastula and leave it in the beginning of gastrulation. At the later developmental stages the newly synthesized RNA passes in the cytoplasm immediately.