Section 5 — Mutagenesis 



5.79. A Comparative Genetic Analysis of the Radio- 

 sensitivity of Germ and Somatic Cells of 

 Monkeys (Macaca mulatta) and Mice. 



M. A. Arsenieva, N. N. Orlova and E. D. Ba- 

 kulina (Moscow, U.S.S.R.). 



The investigation is dedicated to a comparative 

 cytogenetic study of radiosensitivity of germ and 

 somatic (bone marrow) cells of monkeys and 

 mice. The animals were exposed to 10, 25, 50, 

 100, 200 and 400 r of X-rays. 



The comparative analysis carried out at some 

 stages of prophase of meiosis showed that 

 after irradiation by the doses of 10-100 r the 

 genetic radiosensitivity of germinal epithelium 

 of monkeys was 2-25 times higher than that of 

 mice. 



The highest radiogenetic sensitivity of sper- 

 matocytes I of monkeys was found at the stage 

 of diakinesis- metaphase I. In average, Ir. causes 

 at the prophase of meiosis in monkeys, the 

 incidence of 0.15 per cent of chromosome 

 rearrangements as compared with 0.06 per cent 

 in mice. 



The cytohistological analysis of spermatogonia 

 of monkeys, exposed to the doses of 50-100r of 

 X-rays showed that the type B spermatogonia are 

 especially radiosensitive. The death of type A and 

 B spermatogonia occurs after the exposure to the 

 doses mentioned above, at the interphase as well 

 as in the moment, when their division begins. The 

 irradiation of spermatogonia A leads also to the 

 depression of their mitotic activity. There was 

 no renewal of mitotic activity of spermatogonia 

 A after 30 hr following the irradiation. Type A2 

 spermatogonia were found to be more radio- 

 sensitive than the spermatogonia Ai. 



On the whole the radiosensitivity of sperma- 

 togonia of monkeys was found considerably 

 higher than that of mice. 



Cytological investigations of the rate of 

 chromosome aberrations in bone marrow cells 

 of monkeys and mice after exposure to 100, 200 

 and 400 r of X-rays also discovered the higher 

 genetic sensitivity of monkeys. 



The higher genetic radiosensitivity of germ and 

 bone marrow cells of monkeys ascertained by the 

 analysis, points to the necessity of more detailed 

 investigation of the problem of comparative 

 genetic radiosensitivity of mammals in vitro and 

 in vivo including the studies based on the cells of 

 man in tissue culture. 



5.80. Radiosensitivity of Different Meiotic Stages in 

 Rabbioocytes Discovered in Blastocysts. 



W. Kuhlmann (Miinster, Germany). 



Most experiments concerning radiosensitivity 



of different meiotic stages have been made until 

 now in Habrobracon, Drosophila and mice. The 

 aims of such investigations are 



(1) to radiate the different stages as precisely 

 as possible and 



(2) to detect the different categories of damage 

 which are induced in the different meiotic 

 stages by adequate genetic and/or cytological 

 methods. 



For several reasons the rabbit seems to be 

 especially suitable for such experiments : ( 1 ) 

 Since the ovulation is induced only by mating 

 (or pituitary hormons) the stages of meiosis from 

 dictyoten op to telophase II are precisely 

 predictable. (2) Since the implantation is 

 relatively late (7th day) the blastocysts with a 

 great number of calls can be recovered by oper- 

 ating or by sacrificing the animal on the 5th or 

 6th day after mating, and after adequate treating 

 every blastocyst gives some analysable meta- 

 phase-plates for chromosome study. 



In order to detect anomalies it was necessary 

 to analyse the normal chromosome-complement 

 and to set up a karyogram, which revealed a 

 great similarity to the human chromosome- 

 complement, not only in number (44) but also in 

 the morphology — in contrast to the mouse 

 which has got only telocentric chromosomes. 

 The radiation experiments yielded the greatest 

 sensitivity for inducing dominant lethals as 

 measured by degenerating blactocysts shortly 

 before metaphase, that means in diakinesis, 

 while radiation at the time of metaphase (about 

 6 hr after mating) with the same dosis of 100 r 

 remained without detectable effect. The possible 

 reasons for this difference to the results in 

 Habrobracon — not in mice — will be discussed. 

 Experiments for detecting the presumably 

 second sensitive phase shortly after telephase II 

 (see Habrobracon, Drosophila, mice) are not yet 

 completed, likewise the chromosome-studies in 

 blastocysts for cytological evidence of induced 

 mutations and will be reported about at the con- 

 ference. 



5.81. Studies of the Mechanism of the Effect of 

 FUdR on Chromosomes. Sandra Bell and 

 Sheldon Wolff (Oak Ridge, U.S.A.). 



Fluorodeoxyuridine (FUdR) is a specific DNA 

 synthesis inhibitor in virus-infected Escherichia 

 coli W. Taylor et al. < 2 ) have shown that FUdR- 

 treated lateral roots of Vicia faba have chromo- 

 some gaps and are shattered within 3 to 5 hr 

 after treatment. These aberrations were inter- 



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