Autoradiographic analysis of RNA synthesis in the oocyte-nurse cell complex of the polychaete Ophryotrocha labronica.

Females of the polychaete Ophryotrocha labronica have been pulse labelled with [5-3H] uridine, and the incorporation of label into the RNA of the oocyte-nurse cell complex was followed by light and electron microscope autoradiography. Up to its regression the polyploid nurse cell displays an intense synthesis of rRNA and mRNA, which sustains an extensive production of electron-dense protein granules in it. Concomitantly rRNA and mRNA are synthesized also in the oocyte. Short-term treatment (7h) of polychaete females with alpha-amanitin provokes serious disturbances of oogenesis and subsequent embryonic development, irrespective of when it is applied during oogenesis. In contrast actinomycin gives such effects only when it is applied at the onset of oogenesis. A previous investigation has demonstrated that nurse cell granules are gradually exported through an intercellular canal to the oocyte, where a fraction of them is incorporated into the typical yolk granules. The present labelling experiments indicate that nurse cell RNA is associated with the exported yolk precursor material. From inhibition experiments with alpha-amanitin and from in situ hybridizations with a poly(U)probe it appears that mRNA is particularly involved. At the final collapse of the nurse cell practically all its contents are transferred to the oocyte. From that time the ooplasm is found to contain nuage-like RNA aggregates, which in contrast to other [5-3H]uridine-labelled ooplasmic structures (yolk granules, and minor granules and aggregates) have a non-uniform distribution. The possible origin and function of these aggregates is discussed. The investigation indicates that the nurse cell has a significant export of RNA essentially similar to that from insect nurse cells.