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The case for isogenic strains in toxicological screening
Abstract:
The fundamental principle of the controlled experiment is that treated and control groups should be identical, with minimal within-group variability. Toxicologists recognise this and control age, body weight, disease and the physical environment of the test animals. However most toxicological screening in done with genetically variable outbred stocks, even though isogenic inbred strains, F1 hybrids or identical siblings are usually available. The result is poor experiments with the inevitable genetic differences between groups resulting in increased false positive and negative results, and no indication that the response is under genetic control. It is also illogical to treat genetic variation differently from other types of variation. The argument that it is essential to use outbred animals to model outbred man is illogical. If bacteria can be used to model man (as in the Ames test), so can inbred animals. The uncontrolled variation present in an outbred stock can not be used efficiently to increase the range of phenotypes tested because it also introduces "noise" which obscures experimental effects. The use of two or more isogenic strains gives a much more efficient experimental design with low "noise" and an indication of whether the response is under genetic control. Inbred and F1 hybrid strains (but not identical siblings) have the added advantage of an immortal genotype which outlives any individual animal. Such immortal genotypes may be studied in detail to gather background information. Toxicologists should treat genetics like every other variable and control it, using several isogenic strains in cases where testing needs to be done on more than one genotype.
Insights
Using genetically uniform inbred strains in toxicology improves experimental design. This reduces false positives and negatives, providing clearer results on genetic control of toxic responses.
Area of Science:
- Toxicology
- Genetics
- Experimental Design
Background:
- Controlled experiments require identical groups with minimal variability.
- Toxicologists control many factors but often overlook genetic variation by using outbred stocks.
- Genetic differences in outbred animals lead to poor experimental results, including increased false positives/negatives and obscured genetic control.
Purpose of the Study:
- To highlight the limitations of using genetically variable outbred stocks in toxicological screening.
- To advocate for the use of isogenic strains (inbred, F1 hybrids) in toxicological experiments.
- To demonstrate how controlling genetic variation enhances experimental efficiency and data interpretation.
Main Methods:
- Critiquing the current practice of using outbred animal stocks in toxicological screening.
- Proposing the use of isogenic strains, F1 hybrids, or multiple inbred strains for controlled toxicological studies.
- Comparing the efficiency of using outbred versus isogenic strains in experimental design.
Main Results:
- Genetically variable outbred stocks introduce 'noise,' obscuring true experimental effects and hindering the assessment of genetic control.
- Isogenic strains provide a more efficient experimental design with lower 'noise,' allowing for better detection of toxicological responses.
- The use of multiple isogenic strains offers a robust approach to understanding genetic influences on toxicity.
Conclusions:
- Toxicologists should treat genetic variation as a critical variable to be controlled, similar to age or environment.
- Employing isogenic strains significantly improves the reliability and interpretability of toxicological screening data.
- The use of immortal genotypes from inbred and F1 hybrid strains facilitates detailed background research and long-term study.