Microsatellite database for MSM/Ms and JF1/Ms, molossinus-derived inbred strains

Type specimens, taxonomic history, and genetic analysis of the Japanese dancing mouse or waltzer, Muswagneri variety rotans Droogleever Fortuyn, 1912 (Mammalia, Muridae)

In the present paper, the existence and location of the type series of the Japanese dancing mouse or waltzer, Muswagneri variety rotans Droogleever Fortuyn, 1912, are established, and a lectotype is designated. Available type specimens are measured, and some morphological parameters, sex, and general condition of the specimens are recorded. A literature survey was conducted, and an attempt is made to clarify the position of M.wagneri variety rotans in the taxonomy of Mus. A genetic analysis suggests that the type series of the Japanese dancing mouse represent a crossbred, or derivation of a crossbred, between the original Japanese dancing mouse of Musmusculusmolossinus Temminck 1844 origin and European fancy or laboratory mice of Musmusculusdomesticus Schwarz & Schwarz, 1943 origin. Much of their genome was replaced and occupied by Musmusculusdomesticus type genome, probably through extensive breeding with European mice.

A wild-derived inbred mouse strain, MSM/Ms, provides insights into novel skin tumor susceptibility genes

Cancer is one of the most catastrophic human genetic diseases. Experimental animal cancer models are essential for gaining insights into the complex interactions of different cells and genes in tumor initiation, promotion, and progression. Mouse models have been extensively used to analyze the genetic basis of cancer susceptibility. They have led to the identification of multiple loci that confer, either alone or in specific combinations, an increased susceptibility to cancer, some of which have direct translatability to human cancer. Additionally, wild-derived inbred mouse strains are an advantageous reservoir of novel genetic polymorphisms of cancer susceptibility genes, because of the evolutionary divergence between wild and classical inbred strains. Here, we review mapped Stmm (skintumor modifier of MSM) loci using a Japanese wild-derived inbred mouse strain, MSM/Ms, and describe recent advances in our knowledge of the genes responsible for Stmm loci in the 7,12-dimethylbenz(a)anthracene (DMBA)/12-O-tetradecanoylphorbol-13-acetate (TPA) two-stage skin carcinogenesis model.

The Japanese Wild-Derived Inbred Mouse Strain, MSM/Ms in Cancer Research

MSM/Ms is a unique inbred mouse strain derived from the Japanese wild mouse, Mus musculus molossinus, which has been approximately 1 million years genetically distant from standard inbred mouse strains mainly derived from M. m. domesticus. Due to its genetic divergence, MSM/Ms has been broadly used in linkage studies. A bacterial artificial chromosome (BAC) library was constructed for the MSM/Ms genome, and sequence analysis of the MSM/Ms genome showed approximately 1% of nucleotides differed from those in the commonly used inbred mouse strain, C57BL/6J. Therefore, MSM/Ms mice are thought to be useful for functional genome studies. MSM/Ms mice show unique characteristics of phenotypes, including its smaller body size, resistance to high-fat-diet-induced diabetes, high locomotive activity, and resistance to age-onset hearing loss, inflammation, and tumorigenesis, which are distinct from those of common inbred mouse strains. Furthermore, ES (Embryonic Stem) cell lines established from MSM/Ms allow the MSM/Ms genome to be genetically manipulated. Therefore, genomic and phenotypic analyses of MSM/Ms reveal novel insights into gene functions that were previously not obtained from research on common laboratory strains. Tumorigenesis-related MSM/Ms-specific genetic traits have been intensively investigated in Japan. Furthermore, radiation-induced thymic lymphomas and chemically-induced skin tumors have been extensively examined using MSM/Ms.

Devising assisted reproductive technologies for wild-derived strains of mice: 37 strains from five subspecies of Mus musculus

Wild-derived mice have long offered invaluable experimental models for mouse genetics because of their high evolutionary divergence from laboratory mice. A number of wild-derived strains are available from the RIKEN BioResource Center (BRC), but they have been maintained as living stocks because of the unavailability of assisted reproductive technology (ART). In this study, we sought to devise ART for 37 wild-derived strains from five subspecies of Mus musculus maintained at the BRC. Superovulation of females was effective (more than 15 oocytes per female) for 34 out of 37 strains by treatment with either equine chorionic gonadotropin or anti-inhibin serum, depending on their genetic background (subspecies). The collected oocytes could be fertilized in vitro at mean rates of 79.0% and 54.6% by the optimized protocol using fresh or frozen-thawed spermatozoa, respectively. They were cryopreserved at the 2-cell stage by vitrification with an ethylene glycol-based solution. In total, 94.6% of cryopreserved embryos survived the vitrification procedure and restored their normal morphology after warming. A conventional embryo transfer protocol could be applied to 25 out of the 35 strains tested. In the remaining 10 strains, live offspring could be obtained by a modified embryo transfer protocol using cyclosporin A treatment and co-transfer of ICR (laboratory mouse strain) embryos. Thus, ART for 37 wild-derived strains was devised successfully and is now routinely used for their preservation and transportation. The information provided here might facilitate broader use and wider distribution of wild-derived mice for biomedical research.

Independent genetic control of early and late stages of chemically induced skin tumors in a cross of a Japanese wild-derived inbred mouse strain, MSM/Ms

MSM/Ms is an inbred mouse strain derived from a Japanese wild mouse, Mus musculus molossinus. In this study, we showed that MSM/Ms mice exhibit dominant resistance when crossed with susceptible FVB/N mice and subjected to the two-stage skin carcinogenesis protocol using 7,12-dimethylbenz(a)anthracene (DMBA)/ 12-O-tetradecanoylphorbol-13-acetate (TPA). A series of F1 backcross mice were generated by crossing p53(+/+) or p53(+/-) F1 (FVB/N × MSM/Ms) males with FVB/N female mice. These generated 228 backcross animals, approximately half of which were p53(+/-), enabling us to search for p53-dependent skin tumor modifier genes. Highly significant linkage for papilloma multiplicity was found on chromosomes 6 and 7 and suggestive linkage was found on chromosomes 3, 5 and 12. Furthermore, in order to identify stage-dependent linkage loci we classified tumors into three categories (<2mm, 2-6mm and >6mm), and did linkage analysis. The same locus on chromosome 7 showed strong linkage in groups with <2mm or 2-6mm papillomas. No linkage was detected on chromosome 7 to papillomas >6mm, but a different locus on chromosome 4 showed strong linkage both to papillomas >6mm and to carcinomas. This locus, which maps near the Cdkn2a/p19(Arf) gene, was entirely p53-dependent, and was not seen in p53 (+/-) backcross animals. Suggestive linkage conferring susceptibility to carcinoma was also found on chromosome 5. These results clearly suggest distinct loci regulate each stage of tumorigenesis, some of which are p53-dependent.

A deletion in a cis element of Foxe3 causes cataracts and microphthalmia in rct mice

The Rinshoken cataract (rct) mutation, which causes congenital cataracts, is a recessive mutation found in SJL/J mice. All mutants present with opacity in the lens by 2 months of age. The rct locus was mapped to a 1.6-Mb region in Chr 4 that contains the Foxe3 gene. This gene is responsible for cataracts in humans and mice, and it plays a crucial role in the development of the lens. Furthermore, mutation of Foxe3 causes various ocular defects. We sequenced the genomic region of Foxe3, including the coding exons and UTRs; however, no mutations were discovered in these regions. Because there were no differences in Foxe3 sequences between the rct/rct and wild-type mice, we inferred that a mutation was located in the regulatory regions of the Foxe3 gene. To test this possibility, we sequenced a 5' noncoding region that is highly conserved among vertebrates and is predicted to be the major enhancer of Foxe3. This analysis revealed a deletion of 22-bp located approximately 3.2-kb upstream of the start codon of Foxe3 in rct mice. Moreover, we demonstrated by RT-PCR and in situ hybridization that the rct mutant has reduced expression of Foxe3 in the lens during development. We therefore suggest that cataracts in rct mice are caused by reduced Foxe3 expression in the lens and that this decreased expression is a result of a deletion in a cis-acting regulatory element.

Phenotypic and expression analysis of a novel spontaneous myosin VI null mutant mouse

In humans, hearing is a major factor in quality of life. Mouse models are important tools for the discovery of genes responsible for genetic hearing loss, often enabling analysis of the processes that regulate the onset of deafness in humans. Thus far, at least 400 deafness mutants have been discovered in laboratory mouse populations and used in the study of deafness. Here we report the discovery of a new spontaneous recessive Rinshoken shaker/waltzer (rsv) mutant derived from our in-house C57BL/6J stock, which exhibits circling and/or head-tossing behaviour and complete lack of auditory brain response to any sound pressure. The hearing and balance phenotypes are associated with structural defects, in particular, disorganisation and fusion of stereocilia in the inner ear hair cells. Two sets of intersubspecific N(2) mice were generated for the positional cloning of the rsv mutation. The mutant locus was mapped to a 4.8-Mb region of chromosome 9, which contains myosin VI (Myo6), a gene responsible for deafness in humans and Snell's waltzer mutation in mice. The rsv mutant showed reduced expressions of Myo6 mRNA and MYO6 protein in the inner ear. Moreover, no immunoreactivity was observed in the cochlear and vestibular hair cells in the rsv mutant mice. We sequenced the genomic region (30,154 bp) of Myo6, including all coding exons, a non-coding exon, UTRs and the Myo6 promoter; however, no mutation was discovered in these regions. We therefore speculate that loss of MYO6 expression might cause shaker/waltzer behaviour and deafness in the rsv mutant; also, loss of MYO6 expression might be the result of mutations in an unidentified regulatory region(s) of the gene.

Unique inbred strain MSM/Ms established from the Japanese wild mouse

Most laboratory mice belong to a species of house mouse, Mus musculus. So far, at least three subspecies groups have been recognized; domesticus subspecies group (DOM) distributed in western Europe, musculus subspecies group (MUS) distributed in eastern Europe and northeast Asia, and castaneus subspecies group (CAS) found in southwest and southeast Asia including southern China. These subspecies are estimated to have branched off roughly one million years ago. Genetic comparison between subspecies' groups and common inbred strains (CIS) have revealed that the genetic background of CIS is derived mainly from DOM. This shows the importance of non-DOM wild mice as valuable genetic resources. We started to establish our unique strain, MSM/Ms, from MUS in Japan in 1978. In the beginning, we kept wild mice trapped in Mishima in large plastic buckets. In 1979, breeding by sister-brother mating started. The MSM/Ms inbred strain was established in 1986 and 21 years later it reached F(100). During breeding, no significant fluctuations in litter size and sex ratios have been observed. Extensive genetic analyses of chromosome C-banding pattern, biochemical markers and microsatellite DNA (MIT) markers of this strain have demonstrated the characteristics of MUS. A phylogenetic tree constructed from MIT markers has confirmed the MUS nature of MSM strain. Taken together with its genetic remoteness from CIS, MSM appears to maintain many valuable alleles for investigation of biological functions and diseases. Some of these alleles have avoided selection during breeding as either fancy mice or laboratory mice. The MSM-specific genetic traits discovered to date are discussed.

Mouse phenome database

The Mouse Phenome Database (MPD; http://www.jax.org/phenome) is an open source, web-based repository of phenotypic and genotypic data on commonly used and genetically diverse inbred strains of mice and their derivatives. MPD is also a facility for query, analysis and in silico hypothesis testing. Currently MPD contains about 1400 phenotypic measurements contributed by research teams worldwide, including phenotypes relevant to human health such as cancer susceptibility, aging, obesity, susceptibility to infectious diseases, atherosclerosis, blood disorders and neurosensory disorders. Electronic access to centralized strain data enables investigators to select optimal strains for many systems-based research applications, including physiological studies, drug and toxicology testing, modeling disease processes and complex trait analysis. The ability to select strains for specific research applications by accessing existing phenotype data can bypass the need to (re)characterize strains, precluding major investments of time and resources. This functionality, in turn, accelerates research and leverages existing community resources. Since our last NAR reporting in 2007, MPD has added more community-contributed data covering more phenotypic domains and implemented several new tools and features, including a new interactive Tool Demo available through the MPD homepage (quick link: http://phenome.jax.org/phenome/trytools).

Biochemical individuality reflected in chromatographic, electrophoretic and mass-spectrometric profiles

This review discusses the current trends in molecular profiling for the emerging systems biology applications. Historically, the methodological developments in separation science were coincident with the availability of new ionization techniques in mass spectrometry. Coupling miniaturized separation techniques with technologically-advanced MS instrumentation and the modern data processing capabilities are at the heart of current platforms for proteomics, glycomics and metabolomics. These are being featured here by the examples from quantitative proteomics, glycan mapping and metabolomic profiling of physiological fluids.

Cranial bone morphometric study among mouse strains

BACKGROUND

Little is known about the molecular mechanism which regulates how the whole cranium is shaped. Mouse models currently available for genetic research include several hundreds of unique inbred strains and genetically engineered mutants. By cross comparing their genomic structures, we can elucidate the cause of any differences in the phenotype between two strains. The craniometry of subspecies, or closely related species, of mice provide a good systemic model to study the relationship between genetic variance and cranial shape evolution. The lack of a quantified framework for comparing and analyzing mouse cranial shape has been a problem. For this reason, we performed quantitative analysis of cranial shape morphology between several mouse strains.

RESULTS

This article reports on a craniometric assay of seven mouse strains: four inbred strains (C57BL/6J, BALB/cA, C3H/HeJ, and CBA/JNCr) from Mus musculus domesticus (M. m. domesticus); one closed colony strain (ICR) from M. m. domesticus; one inbred strain (MSM/Ms) from Mus musculus molossinus; and, Mus spretus as a strain from a species other than M. m. domesticus. We performed linear measurements and geometric morphometrics. Geometric morphometrics revealed that the cranial characteristics of each strains were clearly distinguishable. We obtained mean scores for each species using the tpsRelw Program and plotted them.

CONCLUSION

Geometric morphometrics proved to be useful for identifying and classifying variations in form, and it revealed that M. spretus has a slender cranium when compared with our other strains. The mean cranial shape of C3H or CBA was more similar to MSM/Ms, which is derived from M. m. molossinus, than to either C57BL/6J, BALB, or ICR which are derived from M. m. domesticus. Future work in this field will aid in elucidating the mechanism of whole cranial shape regulation.

X chromosome reactivation initiates in nascent primordial germ cells in mice

During primordial germ cell (PGC) development, epigenetic reprogramming events represented by X chromosome reactivation and erasure of genomic imprinting are known to occur. Although precise timing is not given, X reactivation is thought to take place over a short period of time just before initiation of meiosis. Here, we show that the cessation of Xist expression commences in nascent PGCs, and re-expression of some X-linked genes begins in newly formed PGCs. The X reactivation process was not complete in E14.5 PGCs, indicating that X reactivation in developing PGCs occurs over a prolonged period. These results set the reactivation timing much earlier than previously thought and suggest that X reactivation may involve slow passive steps.

X chromosome inactivation is a mechanism to compensate gene dosage difference between XY males and XX females in mammals. During early embryogenesis, one of two X chromosomes in every female cell is inactivated, and the inactive X chromosome is stably inherited through cell divisions of somatic cells. Although precise timing is not given, the inactive X chromosome is known to be reactivated during germ cell development. It is generally believed that the dynamics of X chromosome activity is tightly correlated with major genomic reprogramming events occurring during mammalian development. Therefore, elucidation of the X reactivation kinetics is important for understanding the mechanism of X chromosome inactivation/reactivation processes and the epigenetic reprogramming processes as well. Here we investigated when X reactivation is initiated during development of female mouse germ cells. Contrary to the previous suggestions, X reactivation already begins in nascent primordial germ cells in female mice and proceeds gradually requiring a prolonged period. The activity status of the X chromosomes of germ cells appears to vary from cell-to-cell and from gene-to-gene during the reactivation processes. These results indicate that the X reactivation coincides with the formation of germ cells and suggest that this involves slow passive steps.

Putative Chemical Signals about Sex, Individuality, and Genetic Background in the Preputial Gland and Urine of the House Mouse (Mus musculus)

To explore whether preputial gland secretions and/or urine from the house mouse (Mus musculus) can be used for coding information about sex, individuality, and/or the genetic background of strain [ICR/albino, Kunming (KM), and C57BL/6], we compared the volatile compositions of mouse preputial glands and urine using a combination of dichloromethane extraction and gas chromatography coupled with mass spectrometry (GC-MS). Of the 40 identified compounds in preputial gland secretions, 31 were esters, 2 sesquiterpens, and 7 alcohols. We failed to find any compound unique to a specific sex, individual, or strain. However, many low molecular weight compounds between the sexes, most compounds among individuals, and several compounds among the 3 strains varied significantly in relative ratios. These quantitative differences in preputial gland volatiles (analog coding) are likely to convey information about sex, individual, and the genetic background of mouse strain. We identified 2 new main and male-elevated compounds, 1-hexadecanol (Z=3.676, P=0.000, N=19 in ICR; Z=3.576, P=0.000, N=18) and 1-hexadecanol acetate (Z=3.429, P=0.000, N=19 in ICR; Z=3.225, P=0.001, N=18), which were eluted in GC chromatogram after the 2 sesquiterpens. They might also be potential male pheromones, in addition to the well-known E-beta-farnesene and E,E-alpha-farnesene. Additionally, a few compounds including 1-hexadecanol also varied with strains and might also code for genetic information. Of the 9 identified volatile compounds in male urine, (s)-2-sec-butyl-4,5-dihydrothiazole and R,R-3,4-dehydro-exo-brevicomin are known urine-originated male pheromones from previous studies. We also detected 6-hydroxy-6-methyl-3-heptanone, a male urinary pheromonal compound, which had not been directly detected by GC-MS previously. Chemical analysis shows that the genetically more closely related ICR and KM strains had a higher similarity in the volatile compositions of preputial glands and urine than that between ICR or KM and C57BL/6. R,R-3,4-dehydro-exo-brevicomin, in particular, was sensitive to genetic shifts and differed in relative abundance among the 3 strains, whereas (s)-2-sec-butyl-4,5-dihydrothiazole differed between ICR or Km and C57BL/6. Hence, these 2 compounds might code for information about their genetic background.

Mouse Phenome Research: Implications of Genetic Background

Now that sequencing of the mouse genome has been completed, the function of each gene remains to be elucidated through phenotypic analysis. The "genetic background" (in which each gene functions) is defined as the genotype of all other related genes that may interact with the gene of interest, and therefore potentially influences the specific phenotype. To understand the nature and importance of genetic background on phenotypic expression of specific genes, it is necessary to know the origin and evolutionary history of the laboratory mouse genome. Molecular analysis has indicated that the fancy mice of Japan and Europe contributed significantly to the origin of today's laboratory mice. The genetic background of present-day laboratory mice varies by mouse strain, but is mainly derived from the European domesticus subspecies group and to a lesser degree from Asian mice, probably Japanese fancy mice, which belong to the musculus subspecies group. Inbred laboratory mouse strains are genetically uniform due to extensive inbreeding, and they have greatly contributed to the genetic analysis of many Mendelian traits. Meanwhile, for a variety of practical reasons, many transgenic and targeted mutant mice have been created in mice of mixed genetic backgrounds to elucidate the function of the genes, although efforts have been made to create inbred transgenic mice and targeted mutant mice with coisogenic embryonic stem cell lines. Inbred mouse strains have provided uniform genetic background for accurate evaluation of specific genes phenotypes, thus eliminating the phenotypic variations caused by mixed genetic backgrounds. However, the process of inbreeding and selection of various inbred strain characteristics has resulted in inadvertent selection of other undesirable genetic characteristics and mutations that may influence the genotype and preclude effective phenotypic analysis. Because many of the common inbred mouse stains have been established from relatively small gene pools, common inbred strains have limitations in their genetic polymorphisms and phenotypic variations. Wild-derived mouse strains can complement deficiencies of common inbred mouse strains, providing novel allelic variants and phenotypes. Although wild-derived strains are not as tame as the common laboratory strains, their genetic characteristics are attractive for the future study of gene function.

Expression of imprinted genes in cloned mice

Genomic imprinting is a mammalian specific epigenetic modification of the genome. Assessment of the integrity of the imprinting memory in somatic cell cloned animals is important not only for understanding of the "reprogramming" process during cloning by nuclear transfer, but also for the applications of this technique for therapeutic cloning in the future. In this chapter, we summarize the analytical methods for assessment of monoallelic expression of imprinting genes and expression analysis. From a practical point of view, the authors suggest the use of intersubspecific F1 hybrids between the laboratory mouse (Mus musculus musculus) and the JF1 strain (Mus musculus molossinus). We also list the sequence for PCR primers to detect the polymorphism of imprinted genes between musculus and molossinus.

Origins of mouse inbred strains deduced from whole-genome scanning by polymorphic microsatellite loci

Microsatellite loci are uniformly distributed at approximately 100-kbp intervals on all chromosomes except the chromosome Y, and genetic information about more than 9000 loci and high-throughput polymorphism analysis are now available. Taking advantage of these properties, we carried out whole-genome scanning using eight common inbred strains (CIS) of laboratory mice, including A/J, C57BL/6J, CBA/J, DBA/2J, SM/J, SWR/J, NC/Nga, and 129/SvJ, and eight wild-derived inbred strains (WIS), BGL2/Ms, CAST/Ei, JF1/Ms, MSM/Ms, NJL/Ms, PGN2/Ms, SK/CamEi, and SWN/Ms. We selected and located 1226 informative loci at 1.2-cM average intervals on all of the chromosomes of the 16 strains and compared the polymorphisms of the eight CIS with those from the eight WIS as subspecies representatives. More than 50% of the loci can be identified as WIS (therefore, subspecies-specific) alleles in the CIS genomes. We also discovered that the CIS chromosomes form a mosaic structure with an average ratio of domesticus to non-domesticus alleles of 3:1. Furthermore, the domesticus alleles were present much more frequently on the CIS chromosome X than on their autosomes, suggesting that successive backcrossing of non-domesticus stocks to domesticus stocks had been undergone at the beginning of CIS history.

Intestinal tumorigenesis in Min mice is enhanced by X-irradiation in an age-dependent manner

We examined the effect of X-irradiation on intestinal tumorigenesis in Min (multiple intestinal neoplasia) mice. Single whole-body irradiation was given to mice of various ages from newborn to young adults. On the C57BL/6J (B6) background, X-irradiation increased tumor multiplicity of the small intestine exposed at ages from 2-3 days to 24-25 days, with a peak of 2.7-fold increase at 10-12 days of age; exposure at later ages resulted in only a slight increase. X-irradiation also increased colonic tumors; however, the susceptible age period appeared earlier than that of the small intestine; the peak value of 4.6-fold increase was observed in the exposure at around 2-3 days of age. Irradiation at 24 days or later ages showed almost no effect on the colonic tumor induction. On the (B6 x MSM)F1 background, X-irradiation resulted in 2.7-fold increase in the small intestinal tumors, but no increase in the colonic tumors, and besides, the age dependency observed in the small intestinal tumors was much attenuated. Collectively, we conclude that tumorigenic efficacy of X-irradiation in Min mice was determined by the combination of the target organ, the age at exposure, and the genetic background.

Contribution of Asian mouse subspecies Mus musculus molossinus to genomic constitution of strain C57BL/6J, as defined by BAC-end sequence-SNP analysis

MSM/Ms is an inbred strain derived from the Japanese wild mouse, Mus musculus molossinus. It is believed that subspecies molossinus has contributed substantially to the genome constitution of common laboratory strains of mice, although the majority of their genome is derived from the west European M. m. domesticus. Information on the molossinus genome is thus essential not only for genetic studies involving molossinus but also for characterization of common laboratory strains. Here, we report the construction of an arrayed bacterial artificial chromosome (BAC) library from male MSM/Ms genomic DNA, covering approximately 1x genome equivalent. Both ends of 176,256 BAC clone inserts were sequenced, and 62,988 BAC-end sequence (BES) pairs were mapped onto the C57BL/6J genome (NCBI mouse Build 30), covering 2,228,164 kbp or 89% of the total genome. Taking advantage of the BES map data, we established a computer-based clone screening system. Comparison of the MSM/Ms and C57BL/6J sequences revealed 489,200 candidate single nucleotide polymorphisms (SNPs) in 51,137,941 bp sequenced. The overall nucleotide substitution rate was as high as 0.0096. The distribution of SNPs along the C57BL/6J genome was not uniform: The majority of the genome showed a high SNP rate, and only 5.2% of the genome showed an extremely low SNP rate (percentage identity = 0.9997); these sequences are likely derived from the molossinus genome.

Hybrid breakdown caused by substitution of the X chromosome between two mouse subspecies

Hybrid breakdown is a type of reproductive failure that appears after the F2 generation of crosses between different species or subspecies. It is caused by incompatibility between interacting genes. Genetic analysis of hybrid breakdown, particularly in higher animals, has been hampered by its complex nature (i.e., it involves more than two genes, and the phenotype is recessive). We studied hybrid breakdown using a new consomic strain, C57BL/6J-X(MSM), in which the X chromosome of C57BL/6J (derived mostly from Mus musculus domesticus) is substituted by the X chromosome of the MSM/Ms strain (M. m. molossinus). Males of this consomic strain are sterile, whereas F1 hybrids between C57BL/6J and MSM/Ms are completely fertile. The C57BL/6J-X(MSM) males showed reduced testis weight with variable defects in spermatogenesis and abnormal sperm head morphology. We conducted quantitative trait locus (QTL) analysis for these traits to map the X-linked genetic factors responsible for the sterility. This analysis successfully detected at least three distinct loci for the sperm head morphology and one for the testis weight. This study revealed that incompatibility of interactions of X-linked gene(s) with autosomal and/or Y-linked gene(s) causes the hybrid breakdown between the genetically distant C57BL/6J and MSM/Ms strains.

Characterization of diabetes-related traits in MSM and JF1 mice on high-fat diet

We examined the effect of a high-fat diet on the diabetes-related traits of the Japanese Fancy mouse 1 (JF1), MSM, and C57BL/6J (B6J) mice. MSM and JF1 mice were derived from Mus musculus molossinus. B6J is a commonly used laboratory strain, with the vast majority of genome segments derived from Mus musculus domesticus and Mus musculus musculus, and is susceptible to high-fat diet-induced type 2 diabetes. None of the strains showed symptoms of diabetes or obesity when fed a laboratory chow diet. Under a high-fat diet, JF1 mice developed impaired glucose tolerance, hyperglycemia, hyperinsulinemia, and obesity. B6J mice fed a high-fat diet mildly developed these diabetes-related traits compared to JF1 mice fed a high-fat diet. JF1 mice fed a high-fat diet were classified as having type 2 diabetes and were susceptible to high-fat diet-induced diabetes and obesity. On the other hand, MSM mice were resistant to high-fat diet-induced diabetes. These results indicate that the JF1 strain, with its unique genetic origin, is a useful new animal model of high-fat diet-induced diabetes and obesity. Further investigations using JF1 mice will help to clarify the role of the high-fat diet on human diabetes and obesity.

Improved strain distribution patterns of SMXA recombinant inbred strains by microsatellite markers

To develop SMXA recombinant inbred (RI) strains as more valuable genetic resources, 302 microsatellite (Mit) loci were added to the strain distribution patterns (SDP) reported previously. The improved SDP were constructed in a total of 1085 loci containing 484 Mit markers, 571 restriction landmark genomic scanning (RLGS) spot markers and 30 others. This substantially improved SDP can be freely accessed on our homepage (http://www.med.nagoya-u.ac.jp/sisetu/SDP.htm).

Hybrid Breakdown Caused by Substitution of the X Chromosome Between Two Mouse Subspecies

Hybrid breakdown is a type of reproductive failure that appears after the F2 generation of crosses between different species or subspecies. It is caused by incompatibility between interacting genes. Genetic analysis of hybrid breakdown, particularly in higher animals, has been hampered by its complex nature (i.e., it involves more than two genes, and the phenotype is recessive). We studied hybrid breakdown using a new consomic strain, C57BL/6J-XMSM, in which the X chromosome of C57BL/6J (derived mostly from Mus musculus domesticus) is substituted by the X chromosome of the MSM/Ms strain (M. m. molossinus). Males of this consomic strain are sterile, whereas F1 hybrids between C57BL/6J and MSM/Ms are completely fertile. The C57BL/6J-XMSM males showed reduced testis weight with variable defects in spermatogenesis and abnormal sperm head morphology. We conducted quantitative trait locus (QTL) analysis for these traits to map the X-linked genetic factors responsible for the sterility. This analysis successfully detected at least three distinct loci for the sperm head morphology and one for the testis weight. This study revealed that incompatibility of interactions of X-linked gene(s) with autosomal and/or Y-linked gene(s) causes the hybrid breakdown between the genetically distant C57BL/6J and MSM/Ms strains.

Update of Mouse Microsatellite Database of Japan (MMDBJ)

We updated a database of microsatellite marker polymorphisms found in inbred strains of the mouse, most of which were derived from the wild stocks of four Mus musculus subspecies, M. m. domesticus, M. m. musculus, M. m.castaneus and M. m. molossinus. The major aim of constructing this database was to establish the genetic status of these inbred strains as resources for linkage analysis and positional cloning. The inbred strains incorporated in our database are A/J, C57BL/6J, CBA/J, DBA/2J, SM/J, SWR/J, 129Sv/J, MSM/Ms, JF1/Ms, CAST/Ei, NC/Nga, BLG2/Ms, NJL/Ms, PGN2/Ms, SK/CamEi and SWN/Ms, which have not or have only been poorly incorporated in the Whitehead Institute/MIT (WI/MIT) microsatellite database. The number of polymorphic microsatellite loci incorporated in our database is over 1,000 in all strains, and the URL site for our database is located at http:// www.shigen.nig.ac.jp /mouse/mmdbj/mouse.html.

Spontaneous hypomorphic mutations in antioxidant enzymes of mice

An antioxidant enzymatic system is pivotal for aerobic animals to minimize the damage induced by reactive oxygen species. Spontaneous mutant animals with altered antioxidant enzyme activity should be useful for the study of the function of these enzymes in vivo. We examined the nucleotide sequences of the genes for the major antioxidant enzymes, including catalase (Cat), superoxide dismutase (Sod1, Sod2, Sod3), glutathione peroxidase (Gpx1, Gpx2, Gpx3, Gpx4, Gpx5), and glutathione reductase (Gsr) in 10 inbred mouse strains. Nonsynonymous nucleotide polymorphisms were identified in all genes, except for Gpx1, Gpx3, and Gpx4. Notably, the SJL/J mouse strain possessed unique nucleotide substitutions in the Gsr and Sod2 genes, which led to Asp39Ala and Val138Met amino acid substitutions in GSR and SOD2, respectively. The specific activity of GSR of SJL/J mice was reduced to 65% of that of NZB/N mice. In vivo activity, however, was higher in SJL/J, due to upregulated expression of the enzyme. The SOD2 activity in SJL/J mice was reduced to half that of other mouse strains. Consistent with this reduction, oxidative damage in the mitochondria was increased as demonstrated by a decrease of total glutathione and an increase in the levels of protein oxidation. These spontaneous hypomorphic alleles would be valuable in the study of free radical biology.

Mouse models for four types of Waardenburg syndrome

Waardenburg syndrome (WS) is an auditory-pigmentary syndrome caused by a deficiency of melanocytes and other neural crest-derived cells. Depending on a variety of symptoms associated with the auditory-pigmentary symptoms, WS is classified into four types: WS type 1 (WS1), WS2, WS3, and WS4. Six genes contributing to this syndrome--PAX3, SOX10, MITF, SLUG, EDN3 and EDNRB--have been cloned so far, all of them necessary for normal development of melanocytes. Mutant mice with coat color anomalies were helpful in identifying these genes, although the phenotypes of these mice did not necessarily perfectly match those of the four types of WS. Here we describe mice with mutations of murine homologs of WS genes and verify their suitability as models for WS with special interest in the cochlear disorder. The mice include splotch (Sp), microphthalmia (mi), Slugh-/-, WS4, JF1, lethal-spotting (ls), and Dominant megacolon (Dom). The influence of genetic background on the phenotypes of mice mutated in homologs of WS genes is also addressed. Finally, possible interactions among the six WS gene products are discussed.

A Small Deletion Hotspot in the Type II Keratin Gene mK6irs1/Krt2-6g on Mouse Chromosome 15, a Candidate for Causing the Wavy Hair of the Caracul (Ca) Mutation

A new mutation has arisen in a colony of mice transgenic for human α-galactosidase. The mutation is independent of the transgenic insertion, autosomal dominant, and morphologically very similar to the classical wavy coat mutation, caracul (Ca), on chromosome 15. Therefore, we designated this locus the caracul Rinshoken (CaRin). Applying a positional cloning approach, we identified the mK6irs1/Krt2-6g gene as a strong candidate for CaRin because among five Ca alleles examined mutations always occurred in the highly conserved positions of the α-helical rod domain (1A and 2B subdomain) of this putative gene product. The most striking finding is that four independently discovered alleles, the three preexistent alleles CaJ, Ca9J, Ca10J, and our allele CaRin, all share one identical amino acid deletion (N 140 del) and the fifth, CamedJ, has an amino acid substitution (A 431 D). These findings indicate that a mutation hotspot exists in the Ca locus. Additionally, we describe a Ca mutant allele induced by ENU mutagenesis, which also possesses an amino acid substitution (L 424 W) in the mK6irs1/Krt2-6g gene. The identification of the Ca candidate gene enables us to further define the nature of the genetic pathway required for hair formation and provides an important new candidate that may be implicated in human hair and skin diseases.

Unique genetic variation revealed by a microsatellite polymorphism survey in ten wild-derived inbred strains

Here we report on a genome polymorphism survey using 254 microsatellite markers in ten recently wild-derived inbred strains. Allele size analysis showed that the rate of polymorphism of these wild-derived mouse strains when compared with any of the common laboratory strains is on average 79.8%. We found 632 wild-derived alleles that were not present in the common laboratory strains, representing a 61% increase over the genetic variation observed in the laboratory strains. We also found that on average 14.5% of the microsatellite alleles of any given wild-derived inbred strain were unique. Our results indicate that the recently wild-derived mouse strains represent repositories of unique naturally occurring genetic variability and may prove invaluable for the study of complex phenotypes and in the construction of new mouse models of human disease.