ISOLATION AND COMPOSITION OF NUCLEI AND NUCLEOLI 151 



tion of nucleolar migration in amphibian and insect eggs would lead to the 

 belief that the nucleoli might transfer nucleic acid or protein or both from 

 the nucleus to the cytoplasm. Such a transfer would make this type of 

 nucleolus analogous to the secretory granules of cells such as those of the 

 pancreas or salivary glands, which no doubt transfer enzymes from the cell 

 cytoplasm through the cell wall to the ducts of the glands. It is rather ob- 

 vious that the Warren Lewis-type of nucleoli cannot act in the same manner 

 as do migrating nucleoli, and their function may well be quite different. 



Yokoyama and StowelP''^ have claimed that nucleolar size in the acinar 

 cells of the pancreas is significantly increased following pilocarpine injec- 

 tion. Injection of pilocarpine caused the acinar cells to secrete enzymes in 

 the form of zymogen granules, and during regeneration of the granules the 

 nucleolar size was said to increase. (The increase in nucleolar size as indi- 

 cated by the data was however only slight, and there appeared to be a very 

 marked decrease in size later on.) This work has led Yokoyama and Stowell 

 to the conclusion that the nucleolus may perform some function concerned 

 with protein synthesis in the cytoplasm. 



Stowell has also observed an increase in nucleolar volume in hepatic 

 cells following partial hepatectomy,-"^ and the administration of thioaceta- 

 mide is also said to cause increase in nucleolar volume.-^^-^"^ According to 

 Caspersson and Schultz,^"^ nucleoli are large in glandular cells and in cells 

 in which protein synthesis is active. There is a considerable literature on the 

 nucleoli of tumor cells (see reference 186) which shows that tumor cell 

 nucleoli are often very much enlarged, sometimes to the extent of becoming 

 enormous relative to nuclear volume. Vacuolation also often occurs. 



Thus, if an increase in nucleolar size can be taken to indicate an enhance- 

 ment of nucleolar function, it would seem that mammalian cell nucleoli, 

 which presumably are of the Warren Lewis type, have a function connected 

 with cytoplasmic activity, possibly protein synthesis. "Proof" of nucleolar 

 function is however unfortunately still lacking, and available evidence for 

 concrete functions is very meager. 



This brief review on nucleoli has been limited mainly to biochemical 

 considerations, and the relatively enormous cytological literature has 

 hardly been touched. The reader is referred to a forthcoming detailed re- 

 view on the history and present status of biological concepts concerning 

 nucleoli, which is being prepared for the International Review of Cytology 

 by Dr. Vincent, the investigator previously mentioned, who isolated nu- 

 cleoli from starfish eggs. 



"1 H. O. Yokoyama and R. E. Stowell, J. Natl. Cancer Inst. 11, 939 (1951). 



^o^ R. E. Stowell, Arch. Pathol. 46, 164 (1948). 



"3 L. J. Rather, Bull. Johns Hopkins Hosp. 88, 38 (1951). 



20^ A. K. Laird, Federation Proc. 11, 244 (1952). 



2»6T. Caspersson and J. Schultz, Proc. Natl. Acad. Set. U.S. 26, 507 (1940). 



