Aphidicolin-resistant mutator strains of mouse teratocarcinoma

Summary

From among a series of stable, aphidicolin-resistant mutant strains of mouse teratocarcinoma, derived from a multipotent parental line (PSA-1-80), three were selected for further study on the basis of their comparatively high degrees of resistance and elevated frequencies of spontaneous forward mutation to 6-thioguanine and ouabain resistance. Fluctuation tests confirmed that they were mutator strains. Since each of the three mutants was isolated after mutliple rounds of selection, and since a variety of biochemical abnormalities were observed, it is likely that a number of mechanisms, probably consisting of overlapping subsets, determine the phenotypes. Abnormalities in the metabolism of the nucleotide substrates for polymerization are likely to be of major importance in mutants designated Aph-2 and Aph-3, as there were marked alterations in the dCTP and dATP pool sizes. The specific activity of DNA polymerase α was also increased. For the case of Aph-3, which exhibited the greatest (400-fold) increase in resistance to aphidicolin, a mutation in the structural gene for DNA polymerase α may be an additional important component, since in vitro assays revealed that the isolated enzyme was resistant to aphidicolin. For the case of Aph-1 however, only minor alterations in dNTP pools were observed, and there was no increase in the specific activity of DNA polymerase α or in the aphidicolin resistance of the isolated DNA polymerase α, suggesting yet another mechanism(s) underlying the aphidicolin resistance/mutator phenotype. All three mutants formed subcutaneous tumors in syngeneic mice; both Aph-1 and Aph-2 were multipotent; whereas Aph-3 was nullipotent. Since the parental cells and at least one other derivative multipotent mutator strain have been shown to contribute to the development of injection chimeric embryos (Aizawa et al. 1985), it may be possible to investigate certain phenotypic consequences of Aph-1 and Aph-2 in vivo.