National BioResource Project Mice (ENU-mutagenesis)

The mouse has been used as an experimental animal for more than 100 years and, accordingly, an enormous amount of information about its genes and diseases has been accumulated. Since many genetically homogeneous inbred mouse lines have been reared, animal experiments can now be performed with high reproducibility. In addition, owing to its small size and well-characterized genome, advanced genetic manipulation techniques can be applied to this mammal model at an individual level, and experiments and research carried out from the initial to the final stages of disease development can be tracked at the molecular level, which cannot be accomplished using human subjects. Thus, mice have been widely used worldwide as typical model animals for humans for both fundamental research and direct medical applications.

The RIKEN BioResource Center (BRC) was established in 2001. Since then, the Experimental Animal Division has collected, preserved, and provided mice for research purposes. In 2002, the RIKEN BRC launched its activities as a core institution of the National BioResource Project (NBRP). To date, the RIKEN BRC has collected more than 7000 mouse strains and has provided strains developed in Japan to 950 organizations within Japan and 36 other countries. When an article on the RBC was first published in BioResource Now! in December 2005, the number of mouse strains maintained was 1600. Therefore, the number of strains has increased by more than four times during these past eight years. Many genetically modified mouse lines have been produced for research on cancer, the brain, allergies, development, and tissue regeneration in Japan, and high-quality studies have been performed using these mice. Owing to the support and contribution of these high-level research communities, in the past decade, the RIKEN BRC has collected approximately the same number of mouse strains as those contained in similar resource organizations in Europe and the United States (Fig. 1 and Fig. 2).

The quality of materials used for research is one of the most important factors for ensuring reproducibility of the research results. The quality control procedures for mouse resources consist mainly of microbiological monitoring and genetic monitoring. With respect to microbiological monitoring, 24 items, including documenting the main pathogenic microorganisms that could affect the experimental results, have been regularly examined using decoy mice, and the results of these evaluations have been published on the homepage of the Experimental Animal Division.

Until 2013, mouse hepatitis virus and Mycoplasma pulmonis were occasionally detected during monitoring of mice that were deposited from universities and research institutions. Such contaminations were not observed in 2014. However, intestinal protozoa and threadworms are still detected in nearly 50% of mice. Therefore, we are concerned about the spread of intestinal protozoa and threadworms among research colonies in Japan. The BRC has performed caesarean operations and embryo transfer to eliminate microbial contaminations and can therefore provide high-quality specific pathogen-free (SPF) mice with confidence.

Experiments involving genetic manipulation for specific cells, tissues, or organs at arbitrary time periods in mice have been successfully conducted using Cre-loxP^∗1 or TET^∗2 technology. From the standpoints of the reproducibility of animal experiments, 3R^∗3, and legal compliance regarding the handling of genetically modified organisms, the genetic quality of genetically modified mice must be precisely controlled. However, it is difficult to maintain the quality of genetically modified mice at the high level required for research. At sites where research is performed by breeding multiple transgenic and knockout mice, the genetic quality of many types of genetically modified mice must be quickly and exhaustively controlled. The KO-survey polymerase chain reaction (PCR) method [1] (Fig. 3) is used to exhaustively examine various transgenes, and the loxP/Frt-survey method is used for structural examination of the gene construct of a conditional knockout mouse; thus, the BRC can accurately judge the genotype of a genetically modified mouse and provide accurate information about genetically modified organisms.