12 THE OOCYTE 



preliminary reports of these experiments have appeared ( Vincent, 

 1954, 1955a,b). 



When ovaries of A. forbesii were exposed to P^~ at the dose 

 indicated above for periods up to 8 hours at 23° C. and the nu- 

 cleoh were isolated by the distilled water technique, the uptake 

 of radiophosphorus was linear with time (see Fig. 6). As well, 

 P^" was incorporated into nucleolar RNA at about the same, or 

 at a lower, relative rate than it was incorporated into the cyto- 

 plasmic RNA. This relation changes little during the time inter- 

 vals studied (Fig. 7A). 



The radioautographic studies of Taylor (1953) and Ficq (1953) 

 appeared just after the experiments in Figs. 6 and 7 were com- 

 pleted. These workers found that the nucleolus incorporated radio- 

 isotope into RNA up to 100 times more rapidly than the cytoplasm. 

 In the light of these reports, the experiment described above was 

 repeated in conjunction with a radioautographic control as fol- 

 lows. Ovaries were exposed for 6 hours to sea water containing 

 0.25 microcurie of P^~ per milliliter. At the end of this time the 

 ovaries were washed thoroughly, a small piece of tissue was fixed 

 in formalin and processed for radioautography, and the nucleoli 

 were isolated from the remainder of the tissue by the distilled 

 water technique. The relative specific activity of the RNA ex- 

 tracted from the isolated nucleoli and cytoplasm was found to be 

 near unity; this is in agreement with the previous experiments. 

 However, the radioautographs prepared from the fixed tissue in- 

 dicated a much more rapid uptake of P^^ by nucleolar RNA, in 

 agreement with the results of the other workers. This experiment 

 indicated that considerable radioactivity incorporated into RNA 

 was lost during isolation. Further demonstration of loss of radio- 

 activity from the nucleoli during isolation was obtained by smear- 

 ing the homogenates of the oocytes on nuclear track plates (Ko- 

 dak NTB-1) at various steps of the isolation procedure. The 

 nucleoli present in the fresh homogenates gave intense blacken- 

 ing of the plate, whereas only a few dozen reduced silver grains 

 were found under the isolated nucleoli. These results indicated a 

 considerable loss of radioactivity from nucleoli during isolation in 

 the distilled water medium. 



