[Gene activity during embryogenesis of the earthworm Eisenia foetida ((3H)uracil autoradiography and actinomycin D treatment) (author's transl)].

Embryos of Eisenia foetida (Spiralia) have been cultivated with [3H]uracil precursor of RNA at different stages of development from egg to gastrula. The results show that ribonucleic acid synthesis detected by autoradiography begins precociously. During segmentation messenger RNAs are produced by interphase nuclei and liberated in cytoplasm cyclically at mitosis. After the blastula stage rRNAs (nucleoli), which can migrate through the nuclear membranes, predominate. The blastomeres, which contain polar plasm and also mesoderm, already known for its controlling part in embryogenesis after gastrulation, are the seats of the increasingly important ribonucleic acid synthesis. These genetic transcriptions, which are inhibited by actinomycin D, are implicated in the determination of the blastomers and postblastular differentiation. Only the messages required for the segmentation divisions pre-exist in the undivided egg.