THE CHROMOSOMES IN VIRUS-INDUCED MURINE 



LEUKAEMIAS 



P. C. ROLLER, E. LEUCHARS, C. TALUKDAR, and V. WALLIS 



Chester Beatty Research Institute, Institute of Cancer Research, London, England 



INTRODUCTION 



Since the first analysis of the chromosomes in spontaneous and radiation- 

 induced leukaemias by Ford and co-workers (1958), a considerable body of 

 information has been added to our knowledge concerning leukaemias in man, 

 rats and mice. It has been established that viral agents are involved in the 

 leukaemogenic process which occurs not only in mice of AK (Gross, 1951) and 

 C58BL strains (Gross, 1956), but also in leukaemias induced by irradiation in 

 C57BL mice (Lieberman and Kaplan, 1959; Gross, 1959). Cytological analysis 

 of these leukaemic cells has disclosed that the chromosome number often 

 deviates from that found in non-leukaemic cells. Attempts have been made to 

 find some relationship between the irregular chromosome number and the 

 leukaemogenic process. With the aim of throwing more light on this problem, 

 chromosome analysis has been carried out in "spontaneous" AK leukaemias 

 and in those which were induced by the Passage-A virus (cell-free extract 

 from AK leukaemic tissues). The data obtained from our studies are pre- 

 sented below. 



METHODS 



The preparations for chromosome studies were made according to the 

 technique of Ford and Hamerton (1956). Colcemid was injected into mice 

 intraperitoneally (dose: "n" ml of a 0-02% solution where "n" = 2% of the 

 body weight in g). The animals were sacrificed 60-75 minutes later. Cell 

 suspensions made from the thymus, spleen, bone-marrow and enlarged 

 lymph nodes, were pre-treated in hypotonic citrate solution for 20 minutes at 

 37°C and fixed in acetic alcohol (1 : 3). The chromosomes were stained with 

 2% aceto-orcein. Before sacrificing the mice, white blood cell counts were 

 made. 



Transplantation of leukaemia was accomplished by taking 1-5 x 10^ 

 thymus or spleen cells from a leukaemic mouse and injecting them intra- 

 peritoneally into non-leukaemic hosts. 



The mitotic index of various tissues has been estimated by counting the 

 number of cells in prophase and metaphase in 1,000 cells and expressing the 



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