Zellwachstum und RNS-Synthese im Ei-N�hrzellverband von Ophryotrocha puerilis

Abstract

During its growth phase, the oocyte is associated with a single highly polyploid nurse cell. Although the nurse cell contains high amounts of cytoplasmic ribonucleic acid, no RNA seems to be transferred to the oocyte. Autoradiographs prepared after pulse labelling with 3H-uridine indicate that the nuclei of both cell types are actively engaged in RNA synthesis during the whole period of oogenesis. Chromosomal RNA synthesis is most intense in oogonia before onset of the growth period. It still proceeds, although at a lower rate, after termination of oocyte growth when all RNA is lost from the nucleoli. Nucleolar RNA synthesis, on the other hand, is strictly correlated with the growth phase proper. Grain counts on chromatin and nucleoli of both egg cells and nurse cells at all stages of oogenesis indicate that nucleolar and chromosomal RNA synthesis are independent of each other to a large extent. It is thought that the type of RNA synthesized within the nucleolus is essentially ribosomal while the chromosomes are primarily engaged in the formation of messenger RNA.