The HPRT Gene as a Model System for Mutation Analysis
There is now very convincing evidence drawn from many different fields of study to support the hypothesis that carcinogenesis is a multistep process, and that mutations are causally involved in bringing about the changes required for a normal cell to become a malignant cell. (For review see McCormick and Maher, 1994). This understanding has served as our working hypothesis as we investigated the ability of physical or chemical carcinogenic agents to induce mutations in diploid human cells in culture and examined the effect of various DNA repair processes on such mutagenesis. We began by developing methods for culturing diploid human fibroblasts in culture and achieving high cloning efficiencies, using normal DNA repair-proficient fibroblasts, but also cells deficient in one or other DNA repair process, such as nucleotide excision repair derived from patients with genetic predispositions to develop cancer (Maher et al., 1975, 1976). Once cloning efficiencies of 30 to 80% had been achieved, we developed methods to quantify the induction of mutations in the endogenous gene coding for hypoxanthine phosphoribosyl-transferase (HPRT) (McCormick and Maher, 1981; Maher et al., 1977, 1979) or diphtheria toxin resistance (Drinkwater et al., 1982), and later for mutations induced in a bacterial gene, supF, when carcinogen-treated plasmids are allowed to replicate in human cells (Boldt et al., 1991; Mah et al., 1989, 1991; Yang et al., 1987, 1988). Albertini and his colleagues (O’Neill et al, 1990a,b; Albertini, 1985; Albertini et al., 1982) developed techniques to allow similar studies of mutations in the HPRT gene of diploid human peripheral blood T lymphocytes.
KeywordsExcision Repair Nucleotide Excision Repair Xeroderma Pigmentosum Cloning Efficiency Diploid Human Fibroblast
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