Suppression of ribosomal gene expression in oocytes and nurse cells of a polychaete as a result of polyamine synthesis inhibition.

The role of the polyamines in ribosomal gene expression was evaluated in the polychaete Ophryotrocha labronica by analyzing the effects of polyamine synthesis inhibition on RNA synthesis during oogenesis, a period characterized by intense nucleolar activity. At various stages of oogenesis adult polychaete females were blocked in their polyamine synthesis by the addition of 10 mM DL-alpha-difluoromethylornithine (DFMO) to the sea water in which they were cultivated. To monitor RNA synthesis during DFMO treatment the animals were pulse-labeled with [5-3H]uridine and processed for autoradiography. Light and electron microscope autoradiographs demonstrate that DFMO treatment suppresses incorporation of label into nucleolar RNA (rRNA) both in the oocytes and their associated nurse cells. The ultrastructural appearance of both cell types reveals interference with nucleolar and ribosomal activity; the endoplasmic reticulum is deprived of ribosomes, and the production of protein granules (vitellogenesis) is reduced. The high specificity of DFMO for polyamine synthesis and the fact that the effects of DFMO were counteracted by addition of a low concentration (10 microM) of putrescine shows that the observed interference with ribosomal gene expression is indeed due to polyamine deficiency.