The mouse spot test: results with a new cross

Mutagenicity testing with transgenic mice. Part II: Comparison with the mouse spot test

The mouse spot test, an in vivo mutation assay, has been used to assess a number of chemicals. It is at present the only in vivo mammalian test system capable of detecting somatic gene mutations according to OECD guidelines (OECD guideline 484). It is however rather insensitive, animal consuming and expensive type of test. More recently several assays using transgenic animals have been developed. From data in the literature, the present study compares the results of in vivo testing of over twenty chemicals using the mouse spot test and compares them with results from the two transgenic mouse models with the best data base available, the lacI model (commercially available as the Big Blue(R) mouse), and the lacZ model (commercially available as the Mutatrade mark Mouse). There was agreement in the results from the majority of substances. No differences were found in the predictability of the transgenic animal assays and the mouse spot test for carcinogenicity. However, from the limited data available, it seems that the transgenic mouse assay has several advantages over the mouse spot test and may be a suitable test system replacing the mouse spot test for detection of gene but not chromosome mutations in vivo.

Mosaicism: the embryo as a target for induction of mutations leading to cancer and genetic disease

Mosaicism, the existence of "patches" of cells with a genetic constitution that differs from that of other cells of an organism, has been observed in both germinal and somatic tissues of several species, including humans. Mutational events occurring during early embryogenesis can give rise to an organism with a significant number of cells with the mutant genotype in one or more tissues. If this event occurs in a precursor of the germ cells, the mutation can be transferred to subsequent generations. In the F1 generation, this event will usually be perceived as a de novo germinal mutation rather than a transmitted variant allele, unless significant effort is directed toward detecting the mosaicism. Similarly, mutations in oncogenes and tumor-suppressor genes in proliferating somatic cells can generate populations of cells that are at increased risk of transforming into tumor cells. The number of potential preneoplastic cells is larger when the mutagenic event occurs in early development than if it occurs in the mature adult. Experimental data confirm that treatment of the developing embryo or fetus with carcinogenic and mutagenic agents increases the cancer incidence in these animals and the frequency of mutations in the offspring of the animals that were exposed in utero. The available data are conclusive that the developing organism is at risk from exposure to mutagenic and carcinogenic agents. However, the data are insufficient to estimate the level of risk associated with exposures in utero, relative to either the background (spontaneous) level of risk or risk associated with similar exposures to the adult organism.(ABSTRACT TRUNCATED AT 250 WORDS)