Recently, it has become possible to produce small numbers of genetically identical mice by the procedure of fusing individual cumulus cells from an adult female into individual enucleated eggs, thereby providing each egg with a diploid nucleus. This Cumulina family is in its third generation of transfers (Wakayama et al. 1998). Recently, mice have been cloned from fibroblasts derived from adult tail snips (Wakayama and Yanagimachi 1999a,b; Wakayama et al. 1999). In testing situations in which genetic variability is a problem, such clones could provide a uniform population.
The new knowledge gained from model animal research should be applicable to developmental toxicology in at least three important ways:
In developing more effective assays to test for environmental toxicants.
In assessing the risks of known toxicants.
In investigating toxicological mechanisms, the understanding of which will allow development of new therapeutic approaches to toxicant-induced defects.
In keeping with the third charge to the committee to evaluate how this information might be used to improve qualitative and quantitative risk assessment, this section deals primarily with possible new model organism approaches to toxicant detection and to the analysis of the mechanism of action of toxicants on developmental processes. The committee will draw upon these new approaches in Chapters 8 and 9 in proposing a multilevel, multidisciplinary strategy to improve developmental toxicity assessment.
Ideally, scientists would like to have an inexpensive test system analogous to the Ames test, which is used, and sometimes misused, for detecting potential carcinogens. The Ames test was based on the assumption that many carcinogens are mutagens and that most mutagens are carcinogens. This test uses sensitized bacteria to measure the mutagenic activity of test samples. It is inexpensive, rapid, and suitable for testing many compounds under many conditions.