CHROMOSOME ABERRATIONS IN LIVER CELLS IN 

 RELATION TO AGEINGf 



H. J. CURTIS AND CATHRYN CROWLEY 



Biology Department, BrooTchaven National Laboratory, Upton, New York, U.S.A. 



SUMMARY 



The percentage of cliromosomal aberrations present in regenerating liver cells of 

 mice has been scored as a function of (1) age in normal animals, (2) time following 

 neutron irradiation, and (3) age of animals subjected to chronic y-irradiation at 7-5 r/day. 

 It is found that aberrations are very high in neutron-treated animals and even increase 

 to nearly 90 % in succeeding months. With clu-onic y-irradiation the frequency increases 

 somewhat faster than that of the controls, but not nearly fast enough to be accounted 

 for on the basis of a single liit phenomenon. It is concluded that there is chromosome 

 healing foUowmg X- or y-irradiation. 



The somatic mutation theory of ageing was proposed a number of years ago, 

 but because of the fact that direct evidence concerning this theory has been 

 lacking, it has not been widely discussed. This theory postulates that the 

 various somatic ceUs of the body gradually undergo spontaneous mutation. 

 Most of these mutations are not lethal, so as cell division takes place in these 

 cells the mutations are gradually multiplied until a large percentage of the 

 body ceUs contain mutations. Since most mutations are deleterious to the 

 cell, and therefore to the organism, by this process the various organs of the 

 body gradually become less well able to perform their functions. This slowly 

 leads to senesence and finally to death. 



It is weU-known that radiation causes a change in the animal which is 

 either identical to or closely resembles the ageing process. It is also well- 

 known that radiation is a very effective mutagenic agent for aU cells, so these 

 facts argue very strongly in favom' of the mutation theory of ageing. 



Since methods for observing mutations in somatic cells in mammals are 

 lacking, an indirect method has been develojied for this purpose (Stevenson 

 and Curtis, 1961). It consists in scoring the numbers of chromosome aberra- 

 tions visible under the light microscope in regenerating liver cells of the mouse. 

 From work with plants (Caldecott, 1961) it was found that the numbers of 

 aberrations present in the somatic cells of a plant were in all cases directly 

 proportional to the mutations therein as measured by the mutation fre- 

 quency in subsequent generations. If the situation is the same in mammals 

 as in plants, and there is every reason to believe that such is the case, the 



•j" Research carried out at Brookhaven National Laboratory under the auspices of the 

 U.S. Atomic Energy Commission. 



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