Germ cell assays

Several assays have been developed for assessing genetic alterations in germ cells. The information developed can be used for hazard identification in the cancer risk assessment process or, more appropriately, in the development of a genetic risk assessment. The decision of when to conduct a germ cell assay is an important one because the assays are generally expensive and time-consuming. An exception is the use of Drosophila in assays that can serve as a substitute for mammalian assays. 

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Mouse visible or eleetrophoretie specifie-locus tests Assays for skeletal and cataract mutations Cytogenetic analy.sis and heritable translocation assays DNA damage and repair in rodent germ cells Dominant lethal assay... 

Mammalian germ cell cytogenetic assay [OECD 483] /... 

In vivo mammalian mutation tests are not restricted to germ cell tests. The mouse spot test described below is, again, a test used first for studying radiation-induced mutation but has also been used for screening chemicals for in vivo mutagenic potential. This test has had several proponents but compared with in vivo chromosomal assays is not widely used. 

Ehling, U.H., Chu, E.H.Y., DeCarli, L., Evans, H.J., Hayashi, M., Lambert, B., Neubert, D., Thilly, W.G. and Vainio, H. (1986). Report 8. Assays for germ-cell mutations in mammals. In Long-term and Short-term Assays for Carcinogens. (Montesano, R., Bartsch, H., Vainio, H., Wilboum, J. and Yamasaki, H., Eds.). A Critical Appraisal. IARC Scientific Publications, No. 83, Lyon, pp. 245-265. 

Bentley KS, Working PK. 1988. Activity of germ-cell mutagens and nonmutagens in the rat spermatocyte UDS assay. Mutat Res 203 135-142. 

Acrylic acid was not mutagenic in five strains of Salmonella typhimurium with or without metabolic activation by liver micro-somes. Results were also negative (nonmuta-genic) in an number of in vivo assays in both somatic and germ cells. ... 

Dominant lethal assays in mice were performed using o- and p-cresols. Male mice were given a single dose of o-cresol (0, 75, 250, or 750 mg/kg) or p- cresol (0, 100, 275, or 550 mg/kg) by gavage in corn oil and mated to untreated females in order to assess dominant lethal effects. The matings were continued for 6 weeks so that all stages of male germ cell development were tested. 

Each cytogenetic test system has advantages and disadvantages. For instance, if a very simple determination of a compound s ability to produce chromosomal aberrations in vivo is desired, a bone marrow assay is probably simplest and least expensive. If, however, genetic hazards to future generations are of primary concern, assays of germ cells would be more appropriate. In in vitro assays of peripheral lymphocytes or cell lines, the cells can be made synchronous or fairly synchronous. 

Several assays in mammals permit a determination of the incidence of micronuclei 393 of these, the only one sufficiently developed to be a standard assay is the in vivo mammalian bone marrow polychromatic-erythrocyte assay.155 Micronuclei are formed from chromosomes or chromosomal fragments that are not incorporated into daughter nuclei at the time of cell division. Ihus, this very rapid test serves as an in vivo somatic cell screening test for finding genotoxic chemicals that might break chromosomes or cause nondisjunction in germ cells. It has been applied to more than 150 chemicals.158... 

A micronucleus assay can be conducted with bone marrow cells, peripheral lymphocytes or germ cells (spermatids) of mice. Rats can be used for micronucleus assays with bone marrow or spermatogenic cells but the use of peripheral lymphocytes requires surgical removal of the spleen, since this is the predominant site of removal of micronucleated erythrocytes in rats. 

NOTE, Chemicals which are positive in in vitro mammalian mutagenicity assays, and which also show chemical structure activity relationship to known germ cell mutagens, should be considered for classification as Category 2 mutagens. 

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