Section 5 — Mutagenesis 



that in females inseminated with unprotected 

 spermatozoa. 



The irradiation of spermatozoa in CO and N2 

 after a preliminary passage of the gases through 

 the ejaculate diluted with saline solution, 

 revealed a higher percentage of viable embryoes 

 as compared with irradiated controls. 



The highest percentage of normally developing 

 embryoes was observed in females inseminated 

 with spermatozoa irradiated in nitrogen. 



This level was almost four times as higher as 

 in spermatozoa irradiated in the air and only 

 1.5 times lower than in unirradiated controls. 

 The death of embryoes largely occurred in the 

 preimplantation period of development. 



5.76. The Effect of Cysteine Pretreatment on Radi- 

 ation Induced Dominant Lethals in Mice. 



U. H. Ehling (Munchen, Germany). 



Hundred (101 C3H) Fi males 10-12 weeks 

 old were divided into 4 groups. Groups I and II 

 received an intraperitoneal injection of 15 mg 

 cysteine, Groups III and IV an equal volume of 

 saline. Groups I and III were irradiated with 

 600 rads of X-rays. The interval between injection 

 and irradiation was 25-30 min. After treatment 

 each male was caged separately with a hybrid 

 female for a period of 7 days. Every 7th day the 

 females were replaced. The uterine contents of 

 fertilized females were examined 13^ to \6\ days 

 postconception. The proportion of implanted 

 embryos in three successive matings, expressed 

 as percent of controls (Group 11 + IV), was in 

 Group 1 : 88 per cent, 90 per cent, 45 per cent and 

 in Group III: 87 per cent, 84 per cent, 41 per 

 cent. Classifying embryos as alive or dead 

 (including resorption sites) gave the following 

 mean numbers of two respective types per litter 

 in the successive mating series, Group I: 3.9 and 

 4.0; 4.6 and 3.4; 1.0 and 3.1, and Group III: 

 3.8 and 4.0; 4.3 and 3.3; 1.5 and 2.2. The pooled 

 results of both control groups are, Group I: 

 8.5 and 0.5, and Group IV: 8.4 and 0.5. The 

 results clearly demonstrate differences in the 

 effect of cysteine in different stages of sper- 

 matogenesis. More data are being collected to 

 evaluate the response of different gametogenic 

 stages. AET will be used in additional experi- 

 ments. 



5.77. Effect of AET against the Dominant Lethality 

 Induced by X-rays in Male Mice. A. Leonard 

 and J. R. Maisin (Mol, Belgium). 



C+ male mice injected or not with AET (2-(3- 



aminoethylisothiureabromide-hydrobromide or 

 chloride-hydrochloride) were given 400 r on the 

 whole-body or on testes only and mated with 

 virgin females immediately after treatment. 



At the 1 7th day of their pregnancy, the females 

 were dissected and the preimplantation loss and 

 intrauterine death rate scored. AET does not give 

 any protection against dominant lethality induced 

 by 400 r on the spermatozoa: after 400 r, the 

 number of post-implantation deaths increased in 

 the same way in protected and non- protected 

 groups while the preimplantation loss was the 

 same than in the control group. 



These results and the data obtained with 400 r 

 and 1200 r on the dominant lethality induced in 

 spermatogonia and in spermatozoa will be 

 discussed. 



5.78. Population Dynamics of Irradiated Type A 

 Spermatogonia of the Mouse. E. F. Oakberg 

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



Type A spermatogonia are the stem cells of 

 the seminiferous epithelium, and by the process 

 of stem cell renewal, maintain a constant popu- 

 lation while forming an unlimited number of 

 cells which differentiate into spermatozoa. 

 Since the duration of all other spermatogenic 

 stages is short in relation to the total reproductive 

 span, type A spermatogonia are the cells of 

 primary importance in both genetic damage and 

 fertility of irradiated male mammals. Degener- 

 ation of cells in interphase or early prophase 

 reduces type A cells in irradiated testes to a 

 small fraction of control numbers. With acute 

 exposures of 300 r or higher, the surviving cells 

 multiply before differentiation into later stages 

 is resumed. The population dynamics of these 

 few surviving cells, however, is not well under- 

 stood. Our present experiments were stimulated 

 by theobservationt 1 ) that two 500 r doses 24 hr 

 apart gave a mutation rate 5 times that obtained 

 for 1000 r given as a single exposure. Synchro- 

 nization of the cell population by the first dose 

 fraction was suggested as a possible explanation. 

 Our quantitative histological analysis of mouse 

 testes 24 hr after 500 r support Russell's hy- 

 pothesis of a difference in the cell stages present. 

 Type A spermatogonia were almost exclusively 

 in interphase. A few early prophases were 

 counted, but no later mitotic stages were ob- 

 served. Experiments are now under way to 

 determine the relative frequencies of Gi, S and 

 G 2 phases in spermatogonia arrested in inter- 

 phase by irradiation. 



1 Russell, Proc.Natl. Acad. Sci. 48, 1 724-1 727, 1 962 



82 



