102 ROLE OF THE CELL NUCLEUS 



basophilia of the enucleate fragments begins to decrease a couple of 

 days after the section (Brachet, 1955). Even by the 5th day, the 

 staining differences between the nucleate and enucleate halves are 

 very conspicuous ; the nucleate fragments become almost colorless 

 in experiments of longer duration (Figs. 34, 35, p. 111). The cyto- 

 logical structure of the enucleate fragments is also changed : it is 

 now finely granular rather than fibrillar after acid fixation. It is 

 therefore likely that the removal of the nucleus exerts profound 

 effects on the structure of the ergastoplasm. The decrease in baso- 

 philia probably corresponds to the disappearance or reduction in 

 number of the ergastoplasmic "small granules"; the more granular 

 aspect of the ground cytoplasm in the enucleate halves might rep- 

 resent distortion or breakdown of the ergastoplasmic lamellae. 



Recent studies with the electron microscope (Brachet, 1959) have 

 shown that amoebae do not possess a well-organized ergastoplasm. 

 Nevertheless, removal of the nucleus makes the structure of the 

 RNA-containing vesicles much coarser. 



Quantitative estimations of the RNA content (Brachet, 1955) 

 completely confirm the cytochemical observations. The nucleate 

 halves maintain their RNA content constant, even after 12 days of 

 fasting. In the enucleate cytoplasm, on the other hand, there is a 

 steady and marked decrease in the RNA content; it drops by 60% 

 within 10 days. These results have been confirmed by Prescott and 

 Mazia (1954) and by James (1954). The latter claims, however, that 

 the RNA content also drops when intact amoebae are kept fasting. 

 Therefore, the loss of RNA might not be a direct consequence of 

 enucleation; but it has been shown (Brachet, 1955) that the RNA 

 content of fasting whole amoebae remains constant when they are 

 kept under such experimental conditions that they do not markedly 

 decrease in volume. 



These experiments lead to the conclusion that in amoebae the 

 nucleus exerts an important control on the maintenance of cyto- 

 plasmic RNA. Since, in amoebae, almost all of the RNA is localized 

 in the microsome fraction, it can even be said that the small RNA- 

 rich granules of the ergastoplasm lie under close nuclear control. 



Our experimental data on the RNA content of nucleate and 



