27 



THE SPECTRUM OF SENSITIVITY OF DROSOPHILA 

 GERM CELL STAGES TO X IRRADIATION 



Irwin I. Oster* 



Indiana University^ , Bloomington, Indiana, U.S.A. 



Various external and internal conditions are known to affect the sensitivity 

 of chromosomes to ionizing and non-ionizing radiations. Although it has 

 been shown in experiments on many plants and animals that the condensed 

 state of the chromosomes, such as that found during late prophase, metaphase, 

 and anaphase of mitosis and meiosis, is the most susceptible to damage by 

 radiation, the recent findings of Auerbach^, Khishin^ Liining^- *■ ^' ^ and 

 Oster'^, demonstrating the extreme radio-sensitivity of the spermatid stage 

 whose chromosomes are less spiralized than those of spermatozoa in Droso- 

 phila, indicate that this is far from an absolutely valid geneialization. 

 Similarly, notwithstanding the fact that it has been found that lowering the 

 oxygen tension (for instance by the physical exclusion of oxygen or the 

 addition of reducing substances such as sulphite ions) generally reduces 

 radiation-induced damage caused by X-rays in a whole array of organisms 

 ranging from bacteria and higher plants to Drosophila and the mouse, recent 

 work has indicated that the degree of response of different cell stages varies 

 considerably^'^. Because of these discrepancies, which are no doubt in part 

 due to differences in the physiological environment and metabolism of the 

 different organisms studied, it is often difficult to draw any general con- 

 clusions with regard to the processes involved in the production of radiation 

 damage from experiments carried out on heterogeneous groups of plants 

 and animals. In addition, it is known that this heterogeneity exists even at 

 the level of the cell stages which have been treated and studied. Thus it 

 would appear that further work of a more systematic nature along these 

 lines is indicated. While there is no a priori reason to believe that one or even 

 similar mechanisms underlie the sensitivity of all cell stages and organisms 

 to radiation, it seems reasonable to suppose that elucidation of the variation 

 in the sensitivity of different cell stages of one cell type under a variety of 

 conditions may help to shed light on the basis for the differences in radio- 

 sensitivity amongst different organisms. 



For such a determination of the spectrum of sensitivity of one type of cell 

 it would be preferable to use an organism in which genie and chromosomal 

 aberrations can be readily analysed and in which techniques are available 

 for treating sharply defined stages of mitosis and/or meiosis with X-rays 

 under a variety of conditions. We have found that the fruit fly, Drosophila 



* Present address: Division of Chemotherapy, The Institute for Cancer Research, 7701 

 Burholme Avenue, Philadelphia 11, Pennsylvania, U.S.A. 



t This is Zoology Department contribution No. 663. New observations here reported 

 were made with the aid of a grant to Dr. H. J. MuUer and associates from the United States 

 Atomic Energy Commission Contract Ar(l 1-1)-195. 



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