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Research Models
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Mary Parker

Mouse Gene Nomenclature: A Mouse By Any Other Name

The standardization of lab animal nomenclature helps us improve the science

What’s in a name? Would a CB17/Icr-Prkdcscid/IcrIcoCrl , by any other name, show as severe a combined immunodeficiency affecting both B and T lymphocytes?

Laboratory mice may seem to the uninitiated like simple creatures. But when you factor in genealogy, genetic engineering, mutations, etc., it starts to get downright headache-inducing. In fact, whole committees have been established just to standardize nomenclature for mice .

Why Does Proper Lab Mouse Nomenclature Matter?

Beyond scientists loving standardization and precision, it comes down to one of the Three R’s: “Reduction”. Russell and Burch's Three Rs , “Replacement”, “Reduction”, and “Refinement “, were defined in 1959 to not only consider laboratory animal usage from an ethical perspective, but also to improve the science.

Almost all scientific peer-reviewed journals require researchers to be as precise as possible so that other scientists could potentially replicate the results. Replication is a cornerstone of science, but when it comes to lab animals, should never be undertaken without cause. For example, it would be wasteful to replicate a study intended for a Fox Chase SCID (CB17/Icr-Prkdcscid/IcrIcoCrl) mice in an FVB mouse – not only would their immunologic reactions differ vastly but the conclusions of such a study would not be a true replication and possibly a waste of resources.

For true replication to be possible, other researchers must know the precise details of the experiment – including the mouse’s origin and genetics. Simply saying “I used a black 6 mouse” is not enough when there are multiple sub-strains of the C57BL/6 such as the C57BL/6NCrl.

How Does Mouse Gene Nomenclature Work?

Like any new language, in order to read, learning the alphabet and the rules of the language is the first step to communicating with researchers worldwide about your strain of mouse.

The full rules are here , if you require precision, but here is a simple example using a CRL F1 strain:

Mouse gene nomenclature

The uppercase abbreviations denote the two parental strains of which the female strain is always listed first. In this case the hybrid is a C57BL/6NCrl female, indicated by the “B6”, with a C3H/HeNCrl male, indicated by the “C3”. The “F1” lets you know it’s an F1 hybrid and the “/Crl” let’s you know this is housed and bred by Charles River labs.

The important facts for a researcher looking to use a B6C3F1/Crl mouse to know, based on the name, is the animal’s background – whether it is an inbred strain or a hybrid. In this case the mouse is a hybrid of two strains. An F1 hybrid is an outcross, a mating of two unrelated strains, of two inbred strains. F1 hybrids are similar to their inbred parents in that they are the same genetically to each other. However, unlike their inbred parents, brother and sister matings of the F1 offspring, do not result in the same allele pattern as their parents. All of which you know once you understand how to read the nomenclature. 

In deciphering any name there are many important questions you must consider in mouse gene nomenclature:

  • How was the strain bred (ex. Inbred vs. outbred)?

  • Does the model have a spontaneous or a genetically engineered mutation?

  • Is the mutation a targeted mutation (ex. knock-out, knock-in, or floxed)?

  • Is the gene of interest human or mouse origin?

The letters “Tg” could be added to indicate the animal is transgenic whereas the letters “tm” indicate the use of ES cells and targeted mutations to create a line. The abbreviation for the specific gene targeted is then included, and whether the gene is of human or mouse origin is denoted by italics and capitalization of certain letters or the allele number could be included as a superscript. Other information could include a mixed strain background (indicated by a semicolon), or whether it is congenic strain (indicated by a period). The list really does go on.

Finally, the laboratory code or laboratory registration code identifies a particular institute, laboratory or investigator that produced and may hold stocks of a particular strain. Laboratory codes are assigned by the Institute of Laboratory Animal Research (ILAR).

There are many, many more codes and symbols and abbreviations that could appear in a lab mouse gene nomenclature code. Which section is most important depends on what kind of mouse you need for your specific study, but all the information is there.

So what’s in a name? Short version: a whole lot.

To learn more about mouse nomenclature check out these articles, here and here.

Kimberly Jen, DVM, MSc, DACLAM, Senior Staff Veterinarian in Charles River's Research Models and Services contributed to this article.