Quality Considerations in the Use of Animal Models


     
Which elements of quality should you consider when conducting a study with animal models?

Let's start with the definition of quality from Merriam-Webster:

Quality [qual-i-ty] noun
  1. How good or bad something is.
  2. A characteristic or feature that someone or something has, something that can be noticed as a part of a person or thing.
  3. A high level of value or excellence.
There are four elements which affect the quality and performance of animal models: health, genetics, environment and transportation. We'll start this week with the impact of colony health standards and genetic background on the suitability of animal models.

Health Standards

In general, this refers to the level of known pathogenic organisms present in a mouse model. All commercial lab mice providers, and virtually all research animal facilities, perform some level of health testing.

When referring to the health status of a lab mouse, a common abbreviation is SPF (Specific Pathogen Free). Some providers, like Taconic, have their own health standards such as MPF™, which stands for Murine Pathogen Free™.

The important thing to note about the different health designations is what they actually mean. Commercial providers often test for about 60 to 70 organisms.

Animal Model Health Questions

  • What organisms, if any, are present?
  • How will these organisms affect your study?
  • Will your facility veterinarian allow these organisms to enter your animal facility?
When acquiring mice, you can request a health report from the sending facility. Commercial providers often make their health reporting data available online.

While there are approximately 1,000 different bacteria in the mouse gut, very few are tested for during routine health screenings. While most of these organisms would be considered commensal and not pathogenic, the presence or absence of specific organisms can have tremendous effect on research studies.

One of those organisms, Segmented Filamentous Bacteria (SFB) can have dramatic effects on innate immunity. More recently, studies have shown that the presence of gut flora typically found in wild caught mice can have an effect on immune studies in lab mice.

mouse model page View the Taconic White Paper:


Genetic Background

This should be a major quality consideration. If genetics is ignored, it can wreak havoc on your studies.

To misquote Gertrude Stein, "Mouse is a mouse is a mouse is a mouse". Well...not so much. A mouse is a living organism with an active genome, which changes through both spontaneous mutation and active genetic engineering.

While two black mice might look identical to the eye, they could have very different genetic compositions. Even mice with seemingly the same name - such as C57BL/6, C57BL/6N, and C57BL/6J - will have slightly different genetic backgrounds.

The influence of genetics on studies is well known; after all, that is why we have thousands of different strains to choose from when planning a study.

There are two aspects of genetics which you should be aware of and test for when working with genetically engineered animal models.

The first is perhaps the most obvious: testing for the gene which has been manipulated, added, deleted or mutated. This is routinely done by polymerase chain reaction (PCR) testing for the presence or the absence of the desired engineered mutation.

Did you know that genetically engineered genes can change over generations? The process that produces spontaneous mutations in native genes acts just as well on your genetically engineered genes. In addition to testing for the presence or absence of targeted genetic alteration, you should also be testing for changes in copy number.

The second aspect of genetics to consider is the background strain.

Lab Lesson

Tim, the researcher, reads about a model in a paper and requests breeding pairs from the publishing lab. The paper says the model was made on a C57BL/6NTac ES cell line and in discussions with the originating scientist, Tim is told the breeding has continued on C57BL/6. The mice arrive and they have a black coat color. Tim assumes this means they are C57BL/6NTac mice. Tim orders some controls of the same background strain, runs his study and find the results don't make sense. He runs the study again and behold, get the same results. What did Tim forget to do?

Diagnosing a Genetic Problem

If the above researcher had performed Single-Nucleotide Polymorphisms (SNP) testing on his mice, he might have found that sometime in the lineage of this mouse it had been bred to C57BL/10. Could that explain the results?

Maybe.

So now the researcher has to decide whether to pursue backcrossing to make the model congenic on C57BL/6NTac. SNP testing is inexpensive and fast, often delivering results in two weeks or less. When acquiring models from other labs it is always good practice to perform SNP testing and assure you know exactly what the background strain is.

There is much about genetics that is out of our control and driven by biology, we should take the time to understand the genetics of the models we are working with.

Next week we'll discuss the two remaining quality considerations when using laboratory mice: environment and transportation.

mouse model page View the Taconic White Paper: