The ICR mouse is a type of albino laboratory mouse frequently used as a tool in a wide range of biological and medical sciences. Its prevalence in research settings stems from a combination of specific genetic and physical traits that make it a versatile model for studying various biological processes and diseases.
Origins and Key Characteristics
The name “ICR” is an acronym for the Institute of Cancer Research, where the strain was established in 1948. Its lineage, however, traces back to just two male and seven female non-inbred albino mice imported from Switzerland to the Rockefeller Institute in 1926. Descendants of these original mice were sent to different institutions, eventually leading to the development of the Ha/ICR strain.
Being an outbred stock means that ICR mice are intentionally bred to maintain genetic variation. Unlike other types of laboratory mice that are genetically identical, the ICR population has a diverse set of genes, which more closely mirrors the genetic heterogeneity found in human populations. This genetic diversity is a planned and managed characteristic, achieved through specific breeding schemes like the Poiley rotational method to ensure variability is maintained across generations.
Physically, ICR mice are recognized by their albino coat, and they tend to be relatively large compared to some other strains. They are known for being docile, which makes them easy for researchers to handle and work with in a laboratory environment. Furthermore, they have excellent reproductive performance, with high fertility and large litter sizes, averaging around 11.5 pups. This productivity makes them a practical choice for studies that require a large number of subjects.
Common Uses in Research
In toxicology and pharmacology, researchers often need to understand how a new drug or chemical might affect a broad population. Using an outbred stock like the ICR mouse allows scientists to observe a range of responses to a substance, providing insights into how different genetic makeups might influence both the effectiveness and the potential toxicity of a compound. This mimics the real-world scenario where medications are administered to genetically diverse humans.
Because of their robust health and adaptability, ICR mice serve as a reliable general-purpose model. Their use extends to studies on aging, infectious diseases, and vaccine development. In oncology, while highly specific cancer genetics are often studied in other models, ICR mice can be used for more general cancer research.
Distinction from Inbred Strains
To fully appreciate the role of ICR mice, it is useful to contrast them with inbred strains, such as the C57BL/6 mouse. An inbred strain is created through many generations of sibling-to-sibling mating, resulting in a population where every individual is genetically uniform, much like identical twins. This genetic homogeneity is valuable for experiments that require high reproducibility and need to isolate the effect of a single variable, such as one specific gene, on a consistent genetic background.
The choice between an outbred stock like ICR and an inbred strain depends entirely on the scientific question. If the goal is to understand how a particular gene influences a disease, the controlled genetic environment of an inbred strain is ideal. It minimizes background genetic “noise,” making it easier to see the specific effect being studied.
Conversely, if the objective is to assess the safety of a new chemical for the general public, the genetic diversity of the ICR mouse is more informative. The varied responses within the ICR population can help predict a wider range of potential outcomes in humans. This trade-off between the generalizability of outbred stocks and the reproducibility of inbred strains allows researchers to select the most appropriate animal model for their specific experimental needs.