CYTOPLASMIC DNA IN IRRADIATED NEURAL TUBE 85 



rare until cells ha\e undergone at least one mitosis subsequent to irradiation. 

 Micronuclei are more prominent in some material than in others (La Cour, 

 1953). Both the number of fragments per cell and the number of cells with 

 fragments increase with the dose ( Roller. 1947) . At their height, micronuclei 

 may occur in lO^r or more of cells (Gray and Scholes, 1951 : von Sallmann, 

 et al, 1957; Friedkin, 1959). 



Most ideas in the literature as to the nature of the bodies in the cytoplasm 

 are based on interpretations of a static picture rather than on direct obser- 

 vation. Of indisputable origin are micronuclei. Recordings with time-lapse 

 photography have been made of the formation of micronuclei in irradiated 

 cells and of their movement into the cytoplasm (Bajer, 1958; Bloom ct al., 

 1955: Ohnuki and Makino, 1960). The origin of a chromatin body in the 

 cytoplasm through degeneration of a sister nucleus in a cell which did not 

 complete division is well founded in a restricted field ( VVigglesworth, 1942) 

 and has also been observed in irradiated tissue cultures (Stroud and Brues, 

 1954). Direct extrusion of nuclear material into the cytoplasm has ofen been 

 postulated as the method of formation of these bodies, but apparently has 

 not often been observed in irradiated material, nor has the gradual growth 

 of a cytoplasmic body de novo in the cytoplasm, nor actual phagocytosis of 

 degenerated nuclei. 



Our material confirms the observations of others (Butler. 1936; Schneller, 

 1951) working with irradiated chick embryos. Attention has been centered 

 on the large amount of extranuclear Feulgen-positive material present, espe- 

 cially in the neural tube. Apparently the presence of DNA in the cytoplasm 

 is not a universal reaction to irradiation. Mitchell !l942) found the cyto- 

 plasm of irradiated tumor cells consistenly negative to the Feulgen reaction. 



Our material justifies the conclusion that many of the bodies lie within 

 the cytoplasm (Figs. 2-1 1 ) . This could often be demonstrated with the light 

 microscope with Zeiss stereoscopic eye caps to give an exaggerated view of 

 depth. The electron microscope pictures are indisputable (Fig. 12) Wanko 

 etal.,\959. 



Spear and Gliicksmann's i^l938j and Glucksmann's (^1951) distinction be- 

 tween two types of chromatin bodies, depending on whether death of the 

 cell occurred in interphase or in mitosis, aids in identification of certain 



Fig. 2. Feulgen stain of the neural tube of a 3-day chick embryo which had re- 

 ceived 200 r of x-rays 7 hours previously. Many of the cytoplasmic bodies are of com- 

 pound nature (see arrows) containing one or several Feulgen-positive centers, accom- 

 panied by Feulgen-negative material. Compare Fig. 10. Newcomer fixative. X 1200. 



Fig. 3. Brain of a 2'/2- to 3-day chick embryo which had received 200 r of x-rays 

 9 hours previously. The lumen is at the top of the figure. This field shows only minor 

 change compared to much of the embryo. Carnoy fixative : May-Griinwald and Giemsa 

 stain. X 1000. 



