Sister chromatid exchange / editor, Avery A. Sandberg.

Date:
[1982], ©1982
Catalogue details

Licence: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Credit: Sister chromatid exchange / editor, Avery A. Sandberg. Source: Wellcome Collection.

    62/736 (page 40)
    40 / Tice and Schvartzman Ishii and Bender [32] examined the persistence of SCE-inducing DNA lesions induced by mitomycin С (MMC) in human peripheral blood lympho¬ cytes stimulated to proliferate in vitro. Based on the expected geometrical dilution of DNA lesions with each generation and assuming a constant ability of the lesions to induce SCEs, the ratio of non-symmetrical to symmetrical SCEs in third generation metaphase cells indicated a complete absence of DNA repair [32] (Table 3-1). Latt and Loveday [33] induced SCEs with 8-methoxypsoralen plus near UV-light in CHO cells and observed a significant increase in symmetrical SCEs in third generation metaphase cells. The ratio of non-symmetrical to symmet¬ rical SCEs (< 6:1) again indicated persistence of SCE-inducing lesions in¬ duced by the treatment for at least three S phases (Table 3-1). Schvartzman et al. [34] induced SCEs in cells of Allium сера L containing DNA substituted with BrdU with visible light and compared the frequency of non-symmetrical to symmetrical SCEs in third generation metaphase cells. The results indicated complete removal of the SCE-inducing lesions between one S phase and the next (Table 3-1). Finally, Guglielmi et al. [35] exposed human peripheral blood lymphocytes to caffeine throughout the culture period and, after comparing the frequency of symmetrical and non-symmetrical SCEs in third generation metaphase cells, concluded that the caffeine had induced an equal number of SCEs in each generation (Table 3-1). Implicit in this conclusion was the interpretation that if DNA lesions were responsible for caffeine's SCE-inducing ability, the lesions were completely repaired between one S phase and the next. Three-way differential staining. One noteworthy variation in the methodol¬ ogy for examining SCEs in third generation metaphase cells has been proposed by Schvartzman and Goyanes [36]. This approach is based on the use of dis¬ continuous concentrations of BrdU in the cell growth medium. Miller et al. [37] first demonstrated that if mammalian cells were cultured for two consecu¬ tive rounds with BrdU and then transferred to new medium containing only thymidine, the chromosomes of third generation metaphase cells exhibited not two, but three levels of staining. These results were interpreted as signifying a decreasing incorporation of BrdU over the three consecutive cell cycles. The fortuitous decrease in BrdU incorporation during the second replicative cycle was suggested to have resulted from a decrease in the effective concentration of BrdU in the medium. Subsequently, three-way sister chromatid differentia¬ tion (SCD) was also observed in mouse ascites tumor cells in vivo, although in this instance, it was claimed that the staining pattern was the result of an increasing incorporation of BrdU throughout the three consecutive generations [38]. Schvartzman [39] was able to show that three-way SCD could be achieved in the root tip cells of a higher plant by both increasing or