18 THE OOCYTE 



nucleus: one, by specificity being imparted from the gene itself 

 (i.e., DNA structure) to RNA structure through a template 

 mechanism, the other by nucleolar enzymes. If one considers a 

 simple case, that of a cell synthesizing a single specific protein 

 molecule at a rapid rate, the question of template yield becomes 

 significant. That is, can a single genetic locus or "master tem- 

 plate" ( such as would limit the rate of production of any end prod- 

 uct ) produce secondary templates rapidly enough to keep up with 

 inactivation which seems to occur during cytoplasmic synthesis? 

 If not, we can suggest the following as a plausible role for the 

 nucleolus which is at least not contradictory to any evidence 

 presently available and seems to offer possibilities for experimen- 

 tal analysis. 



The nucleolus might be considered to be analogous to a dupli- 

 cating machine with the gene providing the stencil, in that the 

 nucleolus could be assumed to have a specialized mechanism for 

 the rapid synthesis of many new RNA molecules from the specific 

 structure provided by a genetic locus. In this way, identical spe- 

 cific molecules of RNA in large numbers could be manufactured 

 for transfer to the cytoplasm. 



This general pattern of chromosomal, nucleolar, and cytoplas- 

 mic relationships is essentially that advanced by Caspersson and 

 co-workers in 1940 (Caspersson, 1950, pp. 101 ff.) except that 

 Caspersson's group did not have the advantage of the recent dis- 

 coveries regarding the porosity of the nuclear membrane and the 

 actual transfer of RNA to the cytoplasm. Caspersson's group 

 therefore tended to emphasize the participation of basic proteins 

 in the role which is ascribed to RNA in the preceding paragraph. 



Summary 



In this review of some of the many aspects of the origin and 

 development of the oocyte, I have considered in detail only one 

 of the problems which were mentioned in the introduction. In 

 the study of the role of the nucleus in oocyte development re- 

 viewed above, evidence has been presented that indicates that 

 the RNA of the nucleus is intimately involved in the transfer of 

 genetic specificity to the cytoplasm. The nuclear RNA of the 



