February 13, 2023

Transgenic Mice: How they help us understand human disease and development

“Why does NIH fund all these studies about mice?”  My clinical colleague, recently appointed as an advisor to the federal institute asked me this question about twenty years ago when I was working at the Eunice Kennedy Shriver National Institute of Child Health and Human Development. He was not hostile but really wanted to know the answer. “The NIH, he said, is about human disease and our institute is about human development.” I took the time to explain that scientists have used mouse models for human disease and development for over one hundred years. First, as they have short lives, two years at the most in the laboratory and second as they have similar genetics and gene expression (as do other mammals} to humans much can be understood by studying them. In the 1970s, Beatrice Mintz Rudolf Jaenisch developed the first transgenic mouse by inserting viral DNA in the mouse embryo and showed that this inserted gene was found in every cell of the transgenic mouse. As new methods to generate transgenic mice were discovered a revolution in biological science occurred. Scientists understand very well what knock-out and transgenic mice are but to the public these animal models are confusing. First it is possible to silence a specific gene by inserting into a fertilized mouse egg a modification of a particular gene that keeps it from being expressed. These are knock out mice. It is also possible to delete or silence a specific gene in only certain tissues or cells. The mice produced are conditional knock out mice and are useful to study reproductive development (as well as cancer and other diseases). Techniques exist where a gene in a mouse can be silenced or expressed at certain specific times which helps to understand the process of development. It is also possible to produce mice where a gene is overexpressed as well. These transgenic mice have DNA from another animal or a generated mutation sequence put into their DNA. Techniques exist also to allow this expression occur in only certain tissues or cells. It is possible to insert a gene that is tagged with fluorescent or other markers to note over time when the gene is turned on or off, (expressed or not) (1)  These are important models for scientists to study how genes function. Like any research technique the means to generate transgenic mice are constantly being enhanced. Scientists also work to understand insufficiencies in transgenic mouse strains in order to improve these model systems. For instance, a strain developed as a conditional knockout might be shown to be expressed in tissues that are not intended so show expression and thus confound the studies using that particular strain.

Getting back to my colleague’s question, why study mice, or for that matter any animal model?  After all there are many other ways to study disease and human development. There are sophisticated computer data base analyses and stimulations, studies in epidemiology, clinical trials, human genetic studies, and human tissue studies. Isn’t that sufficient? Well actually no. All study methods are important and are complementary in understanding human biology and human disease. Preclinical mouse studies are an excellent method for stand in studies of human disease and for development. They provide a way to find precise details about gene function which leads to other types of essential studies that provide a new understanding of human biology and disease.  Like all research methods, they do have limitations.  It is apparent that humans are diverse. We live in diverse environments, have different eating habits, sleep variations, personal traits that influence our health and wellbeing. Because the laboratory environment is controlled it does not necessarily mimic this diversity.

The Jackson Laboratory in Maine has been a leader in the development of transgenic mice and they understand that inbred strains of mice are not sufficient to study complex diseases. Recently they have developed two projects to deal with this complexity: the Collaborative Cross and the Diversity Outbred strains. These are multi-parent models to explore the intricacy of human biology and disease. Jackson Labs has a vast database on the parents and the environment of these strains (2).

In the past there has been debate among clinicians and scientists as to how useful mouse studies are.  Recently, published studies have attempted to look at the congruence of mouse studies with human disease (3, 4). Often clinicians tend to say there is little congruence while basic scientists tend to say that there is congruence or similarity. Just this month a paper was published by George Tseng of the Department of Biostatistics, University of Pittsburgh proposing a method for determining the issue of how congruent a specific published study is (5).  Scientists are also looking at how certain transgenic mice may not be appropriate as a model due to a problem with the methodology in constructing a transgenic mouse strain. A paper is soon to be published in Biology of Reproduction by MacKenzie Dickson and colleagues at the National Institutes of Environmental Health Sciences. She reports that a Cre recombinase, Amhr2-IRES-Cre (Bhr) that ablates a gene for Anti-mullerian hormone receptor 2  in the ovarian granulosa and in the uterine stroma which was utilized in the development of a  conditional mouse model and used in numerous studies is not as specific as assumed previously. She demonstrated that this particular model displayed global genetic modification and thus casts doubt on previous conclusions of studies using this modified gene (6). The gene in question is for the Anti-mullerian hormone receptor 2 which binds Anti-mullerian hormone. AMH essential in the development of the male reproductive tract is also expressed in the granulosa cells of healthy ovarian follicles and regulates their growth and is found in several uterine diseases such as endometriosis where it is thought to play a role in cell apoptosis or cell death.  

These two recent papers illustrate how science is a process, an always changing understanding of how things work, with each new finding providing further insight into our knowledge of biology. The process of science is like a solving a complex 1000 piece – puzzle that many individuals are a bit familiar with.  In my retirement community residents are always working on such puzzles. At first a person trying to solve the puzzle is confronted with a frustrating time trying to figure out how to put border pieces together. As the puzzle is solved there are surprises. Pieces that an individual thought at first were missing are there in reality and when found are essential in seeing the whole picture. Pieces that a person thought would fit in one place, actually fit in a totally different spot. The process goes on sometimes slowly and sometimes quickly until there is clarity and completion. Then there is always a new puzzle to solve. Scientific investigation is  like this.


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  • Srivastava A, Morgan AP, Najarian ML, Sarsani VK, Sigmon JS, Shorter JR, Kashfeen A,  McMullan RC,  Williams LH, Giusti-Rodríguez P,  Ferris MT, Sullivan P,  Hock P, Miller DR, Bell TA,  McMillan L, Churchill, GA, Pardo-Manuel de Villena F, Genomes of the Mouse Collaborative Cross. Genetics. 2017: 206: 2, 1: 537–556.
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  • Li P, Tompkins RG, Xiao W. The Inflammation and Host Response to Injury Large-Scale Collaborative Research Program. KERIS: kaleidoscope of gene responses to inflammation between species. Nucleic Acids Res. 2017:45(D1):D908-D914. Epub 2016 Oct 26.
  • Zong W, Rahman T, Zhu L, Zeng X, Zhang Y, Zou J, Liu S, Ren Z, Li JJ, Sibille E, Lee AV, Oesterreich S, Ma T, Tseng GC. Transcriptomic congruence analysis for evaluating model organisms. Proc Natl Acad Sci U S A. 2023:120(6):e2202584120
  • Dickson MJ, Gruzdev A, DeMayo FJ, iCre recombinase expressed in the anti-Müllerian hormone receptor 2 gene causes global genetic modification in the mouse, Biology of Reproduction, 2023. ioad012, https://doi.org/10.1093/biolre/ioad012