RNA AND CONTROL OF CELLULAR PROCESSES 101 



many researchers claim was not synthesized in the nucleus? Or, is 

 it a product of a few specially active synthetic sites, as in the nucle- 

 olus? Or, finallv, does it represent biologically inactive RNA which 

 has lost its specificitv through exchange reactions in the cytoplasm 

 and onlv awaits degradation? 



Nuclear Secretion. Granted that RNA is made in the nucleus, it 

 has to be transported into the cvtoplasm, the site of its function. 

 What is known about this transfer? It is surprising to find that this 

 phase of the research of nuclear function has a long history and 

 notable achiev'ements. Many observations on nuclear secretion 

 were, however, made more than fifty years too early, and never 

 struck the imagination of biologists enough to become accepted in 

 a comprehensive theory of gene action. The fact that the nucleus 

 secretes basophilic material was observed by several workers before 

 the end of the previous century. An excellent review of the older 

 literature was written by Maziarski (1910), a disciple of the school 

 of Cracovie, where this phenomenon was studied most actively. A 

 more recent review was written by Hertl ( 1957 ) . One of the reasons 

 why nuclear secretion was not accepted as a general phenomenon is 

 that it was observed in only a few specialized cells with active pro- 

 tein metabolism. 



The first observations were made on the nuclei of the pancreas 

 (Ogata, 1883), which emitted during secretion vesicles of nuclear 

 substance, called plasmosomes or pyrenosomes. Several authors ob- 

 served the nucleolar origin of these plasmosomes. Nuclear secretion 

 can be observed also in most ovocytes. In the cockroach, Peripla- 

 neta, the process of nuclear growth and secretion was studied very 

 carefully more recently (Gresson, 1931). The nucleolus increased 

 in size with the advancing ovocyte's development, and became 

 strongly basophil and irregular in outline. At the same time, it gave 

 rise to emissions which passed through the nuclear membrane to 

 the ooplasm. Later, the nucleolus became larger and vacuolated, 

 giving origin to further extrusions. Once in the cytoplasm, nucleolar 

 extrusions disintegrated and their material became mixed with the 

 cytoplasmic constituents. Around the particles left by disintegra- 

 tion, an accumulation of newly formed vitellus was observed. 



Most of the studies of nuclear secretion emphasized the chromatic 

 nature of the secretion product and often this was considered to be 

 part of the chromosomal chromatin. This is why Hertwig (1902) 



