-13- 



THE ROLE OF RIBONUCLEIC ACID 



AND SULFHYDRIL GROUPS 



IN MORPHOGENESIS 



Jean Bracket 



UNIVERSITE LIBRE DE BRUXELLES 



A good deal of evidence has accumulated in favor of the view that 

 ribonucleoproteins and perhaps ribonucleic acid (RNA) itself play a 

 very important role in morphogenetic processes, especially in the in- 

 duction of the nervous system in amphibian embryos. This evidence 

 will be reviewed here in some detail. 



In the author's opinion, the role played by RNA in morphogenetic 

 processes is only a special case of a more general and fundamental 

 activity of this nucleic acid— its direct intervention in the synthesis of 

 specific proteins. Since the role played by RNA in protein synthesis has 

 been discussed in detail by the author many times (see especially 

 Brachet, 1957) and since this role is now accepted by a vast majority 

 of biochemists and cytologists, this problem will be left out of the 

 present review, which will deal strictly with morphogenetic processes. 



But in morphogenesis— and even in the embryonic development of 

 the vertebrates— induction does not explain everything. Other impor- 

 tant factors, such as mitotic activity, cell movements and adhesion, and 

 capacity to react to an inducing stimulus ( competence ) , also play es- 

 sential parts. We shall see that these processes can be, to a large extent 

 at any rate, controlled by the equilibrium between thiol (-SH) and 

 disulfide (-SS-) in the surrounding medium. Although the action 

 mechanism of this equilibrium remains obscure from the biochemical 

 viewpoint, as we shall see, a very likely explanation of present results 

 is that it acts on the structure of proteins directly involved in morpho- 

 genetic processes. If so, the results obtained in studies on the role of 



241 



