Mutant Mouse Research & Resource Center at the University of Missouri Furthers Model Development for the Community

Figure 1. Armedia O'Neill-Blair, University of Missouri Mutant Mouse Research & Resource Center (MU-MMRRC) Project Manager and Supervisor of Colony Management, handles a mouse from one of the MU-MMRRC’s colonies. The MU-MMRRC provides a unique repository service to the biomedical community by importing, storing and distributing a vast number of mutant mouse strains. Photo courtesy of Dr. Craig L. Franklin, MU-MMRRC.

Laboratory mice are an essential resource for the scientific community. The mouse genome can be manipulated easily, allowing researchers to induce mutations analogous to those that cause disease in humans. As an increasing number of mouse models are created, standardization presents a significant challenge. The University of Missouri Mutant Mouse Research & Resource Center (MU-MMRRC) is supported by ORIP (U42OD010918) to fulfill this emerging need.

The MU-MMRRC is part of a consortium of four Mutant Mouse Research & Resource Centers (MMRRCs) that provide a platform for researchers to share their genetically engineered models. Researchers submit mutant mice that are unique, have been documented in a publication or other publicly available databases, and fill a gap in scientific knowledge. MMRRC staff then cryopreserve the germplasm (e.g., sperm, embryos) and list the model on the MMRRC consortium webpage (mmrrc.org). Researchers from around the world can request mouse models, embryonic stem cells, related reagents, and protocols for their work. Frequently requested models are kept in live colonies for immediate distribution, whereas most are stored as cryopreserved germplasm.

Dr. Craig L. Franklin, MU-MMRRC Co-Director, explained that the consortium works actively to optimize reproducibility and translatability of animal studies by ensuring genetic and infectious disease integrity. When a model is accepted by the MMRRC, background genetic testing is performed to ensure the appropriate mutation is present. The genotype protocol is refined for easier replication, and the background genetics of the mouse are defined precisely. Mice are also rederived into a pathogen-free status and maintained in high-biosecurity facilities to facilitate distribution of high-quality animals.

All four MMRRCs in the consortium participate in broad-based research that can be applied to multiple models. The focus of the MU-MMRRC is to better understand the role of the gut microbiome in model phenotypes. The researchers are defining the following factors: (1) variability in the gut microbiome in contemporary research mouse colonies and factors that influence this variability, (2) effects of gut microbiome variability on model variability, and (3) strategies to address gut microbiome differences that affect model performance.

“We have shown that there is marked variability in the gut microbiome of research mice, and multiple husbandry factors can modulate these populations. However, these differences do not necessarily equate to changes in model phenotype, as differing microbiomes can functionally be very similar,” Dr. Franklin stated.

As a proof-of-concept experiment, the team transferred interleukin-10 knockout embryos into surrogate mothers harboring different microbiomes. Results showed that gut microbiome variability affected model performance, and the team has subsequently found similar results with multiple other models.

Ultimately, these findings will allow for the tailoring of the gut microbiome for optimal translatability to humans. Currently, most laboratory mice are kept in pristine environments with limited antigen exposure. Many viruses and bacteria endemic to wild mouse populations have been excluded to keep colonies healthy and eliminate sources of experimental variability. These conditions foster a limited gut microbiome that Dr. Franklin stated results in an immune system that is more like that of a neonatal human.

Wild and pet mice, in contrast, have been shown to harbor richer gut microbiota and have immune systems more translatable to adult humans.¹ Dr. Franklin and his colleagues are investigating how to increase the antigenic experience in mouse models without reintroducing pathogens that the scientific community has worked diligently to exclude.

Figure 2. Becky Dorfmeyer, a technician at the MU Metagenomics Center, performs DNA extraction for fecal microbiome analysis. Photo courtesy of Dr. Craig L. Franklin, MU-MMRRC.

Dr. Franklin explained that subtle shifts in the gut microbiota occur when mice are transferred from one location to another. Types of bedding, minor housing differences, and water purification methods can affect the gut microbiome. The research team also observed, however, that gut microbiome shifts can occur even when husbandry factors are tightly controlled. These findings illustrate the difficulty of complete standardization across facilities. Dr. Franklin asserted that this microbiotic variation could offer benefits for researchers.

“If we get the same results from mice that have subtly different microbiomes—or even markedly different microbiomes—that [finding] in itself may be [considered] more robust data that applies to the human condition,” he stated.

Dr. Franklin cautioned that shifts seen in the mouse microbiome with location changes are subtle and might be insufficient to influence the model phenotype. He advised researchers to house microbiota-defined mice in individually ventilated caging and handle them only with fresh personal protective equipment.

Researchers also are encouraged to bank feces upon receipt of the new mice and at regular intervals afterwards. Dr. Franklin explained that if a change in phenotype is associated with microbiome drift, the banked feces can be used to re-establish the original microbiome and determine whether any observed phenotypic changes coincided with changes in the gut microbial population.

Recently, the development of models for COVID-19 has represented an area of significant importance for public health. The MU‑MMRRC is helping to fill critical knowledge gaps on gut microbiota and COVID-19. Drs. Franklin and James Amos-Landgraf, an MU-MMRRC co-investigator, recently were awarded supplemental funding to refine and optimize mouse models for the study of SARS‑CoV‑2 infection. They are leading a team to characterize the effect of selected viral and bacterial antigen exposures on model phenotypes. Results will be made immediately available to the biomedical research community.

Researchers who are curious about the effects of the gut microbiome on their model can collaborate with the MU-MMRRC to rederive transgenic mice using mothers from different microbiota-defined colonies. Currently, the gold standard for microbiota transfer is embryo transfer, which is expensive and requires expertise. Dr. Franklin noted that early data indicate that cross‑fostering could be a more user-friendly alternative for microbiome transfer.

Dr. Franklin concluded by providing his perspective on the future of mouse model research. He remarked that the community is shifting away from the concept that enteric disease is caused by single agents and working toward a community influence approach. In this approach, community shifts could be associated with the onset of various disease states. Dr. Aaron Ericsson, University of Missouri Metagenomics Center Director and an MU-MMRRC co-investigator, is pursuing research to further understand this topic.

For more information on the MMRRC program, please visit the Mutant Mouse Resource & Research Centers.

References

¹ Ericsson AC, Montonye DR, Smith CR, et al. Modeling a superorganism—Considerations regarding the use of “dirty” mice in biomedical research. Yale J Biol Med. 2017;90(3):361–371.