REGENERATION 133 



acriflavin had the same effect whether administered before or 

 during the acriflavin treatment, and hence it appeared that inhi- 

 bition by acriflavin is non-competitive. He could not say whether 

 the effect is physical or chemical. 



This inviting biochemical approach to cell differentiation as 

 expressed in oral primordium formation in Stentor is being pursued 

 further by A. H. Whiteley. He is finding (unpublished) that both 

 the purine analogue, 8-azaquanine — which gave no effect for 

 Weisz — and the pyrimidine analogue, 2-thiocytosine, completely 

 block anlagen formation in coeruleus. The inhibition is reversible, 

 and regeneration of animals returned to lake water indicates that 

 this result is probably not due to toxicity but to interference with 

 the formation of nucleic acids which incorporate purines and 

 pyrimidines. Moreover, in the case of 8-azaquanine the effect is 

 counteracted by the presence of normal components of nucleic 

 acids, i.e., hydrolyzed yeast RNA or by RNA directly. And the 

 impHcation of RNA in primordium formation is further indicated 

 by Whiteley's finding that a certain concentration of the RNA- 

 destroying enzyme, ribonuclease, can also block regeneration. 

 The abolition of this effect by added RNAimpKes that the RNAase 

 was in fact producing this blockage through destruction of 

 ribonucleic acids. 



Similarly, but at a wider range of concentrations, 5-methyl- 

 tyrosine prevented regeneration without appreciable toxic side- 

 effects. Since this compound is an antimetabolic analogue of 

 adenosine found in most proteins, the result, in this case was 

 probably due to the blockage of protein synthesis. Therefore it 

 appears that primordium formation in which thousands of new 

 cilia are produced does involve extensive protein synthesis and 

 not merely the translocation of proteins already formed, as well 

 as that RNA is equally implicated, in accordance with the hypo- 

 thesis that RNA guides protein synthesis (Brachet, 1957). 



A satisfactory elucidation of the intimate material basis of the 

 elaboration of cell differentiations is rendered promising in regard 

 to Stentor by the fact that several treatments inhibit oral anlagen 

 formation, presumably by affecting separate, essential aspects of a 

 complex process. Even simple salts in very dilute solution also 

 delay or prevent regeneration or inhibit primordium develop- 

 ment (see p. 254). Moreover, regeneration may be blocked by 



