4 THE OOCYTE 



striking that they have long been correlated with the cytoplasmic 

 changes which occur. The tremendous enlargement of the nu- 

 cleus, specialized modifications of chromosomal structure, and 

 the formation of very large or very many nucleoli, have been in- 

 terpreted as a reflection of nuclear intervention in cytoplasmic 

 differentiation and growth. The many morphological studies of 

 oocyte development have generally led to the conclusion that the 

 nucleoli and the nucleic acid content of the nucleus play a major 

 role in the oocyte. These studies include those of Montgomery 

 (1898), Brachet (1950, 1955), Painter and Taylor (1942), Pani- 

 jel (1951), and Wittek (1952). 



My own cytochemical and biochemical studies on the role of 

 nucleoli and nucleic acids in the development of the egg are pri- 

 marily concerned with ribonucleic acid (RNA). RNA has been 

 assumed to be related to the synthetic activity of cells since the 

 pioneering studies of Caspersson and co-workers and, independ- 

 ently, Brachet, in the late nineteen thirties (Brachet, 1950; Cas- 

 persson, 1950). Both of these workers believed that nuclear RNA 

 was somehow involved in the cytoplasmic expression of genetic 

 activity. This concept has attained new importance in a more 

 specific way in that RNA has been repeatedly suggested as an 

 agent which could receive genetic specificity residing in nuclear 

 deoxyribonucleic acid and transfer this specificity to synthetic 

 centers in the cytoplasm (Bounce, 1953; Rich and Watson, 1954; 

 Goldstein and Plaut, 1955; Lockingen and DeBusk, 1955; Gamow 

 and Yeas, 1955). 



In the experiments reviewed below, the starfish oocyte has been 

 used in the study of nuclear RNA. These oocytes can be obtained 

 readily in all stages of development, and in large quantities. They 

 have a large nucleus and nucleolus, the latter of which can be 

 isolated in considerable quantity. In addition, the nucleolus of 

 the starfish oocyte appears to contain all the RNA of the nucleus 

 (Vincent, 1952). By combining qualitative and quantitative his- 

 tochemistry with direct chemical analyses of isolated nucleoli, it 

 has been possible to study certain aspects of RNA metabolism in 

 the starfish oocyte as it relates to the functional activities of this 

 cell. 



