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Mutant mouse models are indispensable tools for clarifying the functions of genes and elucidating the underlying pathogenic mechanisms of human diseases. We carried out large‐scale mutagenesis using the chemical mutagen N‐ethyl‐N‐nitrosourea. One specific aim of our mutagenesis project was to generate novel cancer models. We screened 7012 animals for dominant traits using a necropsy test and thereby established 17 mutant lines predisposed to cancer. Here, we report on a novel cancer model line that developed osteoma, trichogenic tumor, and breast cancer. Using fine mapping and genomic sequencing, we identified a point mutation in the adenomatous polyposis coli (Apc) gene. The Apc1576 mutants bear a nonsense mutation at codon 1576 in the Apc gene. Although most Apc mutant mice established thus far have multifocal intestinal tumors, mice that are heterozygous for the Apc1576 mutation do not develop intestinal tumors; instead, they develop multifocal breast cancers and trichogenic tumors. Notably, the osteomas that develop in the Apc1576 mutant mice recapitulate the lesion observed in Gardner syndrome, a clinical variant of familial adenomatous polyposis. Our Apc1576 mutant mice will be valuable not only for understanding the function of the Apc gene in detail but also as models of human Gardner syndrome.

Mutant mouse models are indispensable tools for clarifying the functions of genes and for elucidating the underlying pathogenic mechanisms of human diseases. Currently, several large-scale mutagenesis projects that employ the chemical mutagen N-ethyl-N-nitrosourea (ENU) are underway worldwide. One specific aim of our ENU mutagenesis project is to generate diabetic mouse models. We screened 9375 animals for dominant traits using a clinical biochemical test and thereby identified 11 mutations in the glucokinase (Gk) gene that were associated with hyperglycemia. GK is a key regulator of insulin secretion in the pancreatic beta-cell. Approximately 190 heterozygous mutations in the human GK gene have been reported to cause maturity onset diabetes of the young, type 2 (MODY2). In addition, five mutations have been reported to cause permanent neonatal diabetes mellitus (PNDM) when present on both alleles. The mutations in our 11 hyperglycemic mutants are located at different positions in Gk. Four have also been found in human MODY2 patients, and another mutant bears its mutation at the same location that is mutated in a PNDM patient. Thus, ENU mutagenesis is effective for developing mouse models for various human genetic diseases, including diabetes mellitus. Some of our Gk mutant lines displayed impaired glucose-responsive insulin secretion and the mutations had different effects on Gk mRNA levels and/or the stability of the GK protein. This collection of Gk mutants will be valuable for understanding GK gene function, for dissecting the function of the enzyme and as models of human MODY2 and PNDM.

Wnt/β-catenin signalling regulates numerous developmental and homeostatic processes. Ctnnb1 (also known as β-catenin) is the only protein that transmits signals from various Wnt ligands to downstream genes. In this study, we report that our newly established mouse strain, which harbours a Cys429 to Ser missense mutation in the β-catenin gene, exhibited specific organ defects in contrast to mice with broadly functioning Wnt/β-catenin signalling. Both homozygous mutant males and females produced normal gametes but were infertile because of abnormal seminal vesicle and vaginal morphogenesis. An ins-TOPGAL transgenic reporter spatiotemporally sustained Wnt/β-catenin signalling during the corresponding organogenesis. Therefore, β-cateninC429S should provide new insights into β-catenin as a universal component of Wnt/β-catenin signal transduction.

A systematic and comprehensive phenotyping platform has been developed by the RIKEN ENU-mutagenesis project between 1999 and 2007. As a result of phenotype screening on this platform, we have discovered about 400 mutants as animal models for human diseases. All information regarding these mouse mutants is now available to the public through our home page (http://www.brc.riken.jp/lab/gsc/mouse/indexJ.html). In 2008, we reconstructed the existing phenotyping platform and built a new platform. The new system has a hierarchical structure, consisting of a fundamental pipeline that utilizes the existing platform and an additional pipeline, which is optimized for more in-depth phenotyping assays. Using this system, we have started to perform more comprehensive phenotyping of mouse mutants. We have opened this system to Japanese scientists as the Japanese Mouse Clinic. It is anticipated that existing mouse mutants will be reevaluated as disease models by identifying novel phenotypes on the new platform. We will share detailed information about the standard operating procedures (SOPs) of our phenotyping analyses with other related large-scale projects, such as the European Mouse Disease Clinic (EUMODIC) and the German Mouse Clinic (GMC). Moreover, we will contribute to international efforts to standardize mouse phenotype data by sharing annotation of mutant phenotypes, which are made by internationally standardized methods, with other related projects.

A mouse ENU-mutagenesis program at RIKEN GSC has been initiated to conduct a large-scale, genome-wide, early- and late-onset phenotypic screen of mutant mice. We screened about a hundred mice every week with a comprehensive set of phenotype assays including behavioral tests based on a modified SHIRPA protocol, blood tests (both clinical biochemical testing and hemogram), and measurement of locomotor activity in their home cages. To manage the entire program, we developed a client/server architecture database system and named it MUSDB (Mutagenesis Universal Support DataBase). It manages mouse husbandry, mating protocols, procedures for ENU injection and phenotypic screens, phenotype inheritance tests, preservation of sperm and organs, and other materials generated during the program. We have implemented MUSDB in quite a large-scale system that includes 150 client computers. It has, helped reduce typographical errors and provided simple and efficient operation via its front-end user interface. It significantly contributed to the communication within and between workgroups in the program and in the accumulation of various phenotypic and inheritance data.