HGPRT locus

Kao and Puck, 1968) have attributed classic status to this X-linked gene. Indeed, it has become a standard against which all other development in this field must be measured. For this reason, we felt it necessary to first acquaint ourselves with the HGPRT locus before striving to develop other loci in the Fischer L5178Y mouse lymphomacell system (Fischer, 1958). 

Initially, we became attracted to the potential of L5178Y. cells because of a number of characteristics which would seem to favor their use in an in vitro mammalian cell mutational assay system. These include growth in suspension culture, a short generation time of 11 hr, and a cloning efficiency of up to 100% in a simple soft-agar cloning medium. 

We describe in this chapter our experience with the X-linked HGPRT locus and compare some of the results derived from studies with this locus to those obtained with the newly developed thymidine kinase locus, which we believe to be autosomal. Details of the methodology are described, and an attempt is made to compare the utility ofL5178Y cells to that of other cell lines used for specific-locus mutational assays. 

Survival of such metabolically deficient cells is predicated on the existence of an alternate pathway by which guanine nucleotides are generated de novo. In fact, this is the prime pathway leading to purine nucleotides, while the HGPRT-mediated route is generally considered a salvage pathway of far less metabolic importance. 

Once HGPRT-deficient mutants have been isolated by cloning in selection medium, revertants can be selected by taking advantage of another type of selection medium—in this case, medium containing 

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Bootman, J., G.Hodson-Walker, and J.M.Lloyd. 1988b. CFC141b Investigation of mutagenic activity at the HGPRT locus in a Chinese hamster V79 cell mutation system. 88/ PSV005/257, Life Science Research Laboratory, EYE, Suffolk, England (Cited in ECETOC 1994). 

V79 System. The Chinese hamster V79 line was established in 1958 (Ford and Yerganian, 1958). Publication of the use of the line for mutation studies (by measuring resistance to purine analogues due to mutation of the Hgprt locus) occurred 10 years later (Chu and Mailing, 1968). The V79 line was derived from a male Chinese hamster hence, V79 cells possess only a single X chromosome. 

Paschin YV, Bahitova LM. 1982. Mutagenicity of benzo[a]pyrene and the antioxidant phenol at the HGPRT locus of V79 Chinese hamster cells. Mutat Res 104 389-393. 

Fox, M. Delow, G.F. (1985) Tests for mutagenic activity at the HGPRT locus in Chinese hamster V79 cells in culture. In Ashby, J., de Serres, F.J., Draper, M., Ishidate, M., Jr, Margolin, B.H., Matter, B.E. Shelby, M.D., eds, Progress in Mutation Research, Volume 5, Evaluation of Short-Term Tests for Carcinogens. Report of the International Programme on Chemical Safety s Collaborative Study on in vitro assays, Amsterdam, Elsevier Science, pp. 517-523... 

Fox, M. Delow. GF. (1985) Tests for mutagenic activity at the HGPRT locus in Chinese hamster V79 cells in culture. Prog. Mutat. Res., 5, 517-523... 

Moore, M.M., Parker, L., Huston, J., Harrington-Brock, K. Dearfield, K.L. (1991) Comparison of mutagenicity results for nine compounds evaluated at the hgprt locus in the standard and suspension CHO assays. Mutagenesis, 6, 77-85... 

Prenatal and postnatal development rats Genetic toxicology Ames test, chromosomal aberrations in mammalian cells, micronuclei in mice, gene mutation at the HGPRT locus Carcinogenicity none... 

Not genotoxic (Ames, in vitro chromosomal aberrations in mammalian cells, in vivo mouse MN, in vitro gene mutation of HGPRT locus)... 

The cytotoxic, clastogenic and mutagenic effects of HD in Chinese hamster ovary cells have also been evaluated by Jostes et al. (1989). Chromosomal aberration frequency increased in a dose-dependent manner over the dose range of 0.0625 to 0.25 pM. Mutation induction at the HGPRT locus was sporadic, but the majority of the exposures resulted in mutation frequencies that were 1.2 to 4.0 fold higher than the spontaneous frequencies. 

Cytogenetic examination of bone marrow cells showed no increase in aberrations in maternal and neonatal rats following maternal oral exposure to a DeBDE and NoBDE mixture. In vitro assays found that DeBDE did not induce gene mutations in several bacterial tests (Ames assays) or in mammalian cells. DeBDE also did not induce chromosomal aberrations in Chinese hamster ovary cells. However, exposure to the congeners 2,2, 4,4 -tetra-BDE, 3,4-diBDE, and 2-monoBDE caused increased recombinogenic activity at the HGPRT locus in several cell lines. 

CR is stated not to be genotoxic in a Salmonella bacterial mutagenicity test, a CHO forward gene mutation test (HGPRT locus), mouse lymphoma cell assay (L5178Y/tk+/tk ), and a micronucleus test (Colgrave et al, 1983). 

V79 Chinese hamster lung HGPRT locus, forward mutation 6-TGr 2, 43, 39... 

Paschin YV, Kozachenko VL, Sal nikova LE (1983) Differential mutagenic response at the HGPRT locus in V-79 and CHO cells after treatment with chromate. Mutat Res 122 362-365 Patterson RR, Fendorf S, Fendorf M (1997) Reduction of hexavalent chromium by amorphous iron sulfide. Environ Sci Technol 31 2039-2044... 

However, under these conditions SAB does not increase the frequency of gene mutations at the HGPRT locus (Table 1). 

The long-term rat liver epithelial lines are used for mutagenesis studies because of the need for cell proliferation in such studies. The mutation that has been studied is in the hypoxanthine-guanine phosphoribosyl transferase (HGPRT) locus. This locus is on the X chromosome, and therefore only one... 

J. P. O Neill, P. A. Brimer, R. Machanoff, G. P. Hirsch, and A. W. Hsie, A quantitative assay of mutation induction at the HGPRT locus in Chinese hamster ovary cells (CHO/ HGPRT system) Development and definition of the system, Mutat. Res. 45, 91-101 (1977). 

Comparison of Mutation at the hgprt Locus in Different Human... 

One may compare mutation at the tk locus (FsTdR resistance), at the hgprt locus (6TG resistance), and at the Na /K ATPase locus (OU resistance) via the data in Table 2. While the number of experiments performed to date is small, the mutagens are diverse. In each experiment, mutation for all three markers was measured in the same mutagenized population. 

J. G. DeLuca, J. Krolewski, T. R. Skopek, D. A. Kaden, and W. G. Thilly, 9-Amino-acridine—A frameshift mutagen for Salmonella typhimurium TA 1537 inactive at the hgprt locus in human lymphoblasts, Mutat. Res. 42, 327 (1977). 

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