Laboratory Mice Mus Musculus Research Articles

Anatomic and Molecular Correlates of Divergent Selection for Basal Metabolic Rate in Laboratory Mice

Proximal mechanisms describing the evolution of high levels of basal metabolic rate (BMR) in endotherms are one of the most intriguing problems of evolutionary physiology. Because BMR mostly reflects metabolic activity of internal organs, evolutionary increase in BMR could have been realized by an increase in relative organ size and/or mass-specific cellular metabolic rate. According to the "membrane pacemaker" theory of metabolism, the latter is mediated by an increase in the average number of double bonds (unsaturation index) in cell membrane fatty acids. To test this, we investigated the effect of divergent artificial selection for body-mass-corrected BMR on the mass of internal organs and the fatty acid composition of cell membranes in laboratory mice (Mus musculus). Mice from the high-BMR line had considerably larger liver, kidneys, heart, and intestines. In contrast, the unsaturation index of liver cell membranes was significantly higher in low-BMR mice, mainly because of the significantly higher content of highly polyunsaturated 22 : 6 docosahexanoic fatty acid. Thus, divergent selection for BMR did not affect fatty acyl composition of liver and kidney phospholipids in the direction predicted by the membrane pacemaker theory. We conclude that an intraspecific increase in BMR may rapidly evolve mainly as a result of the changes in size of internal organs, without simultaneous increase of the unsaturation index in cell membrane lipids.

Comparative chromosome painting map between two Ryukyu spiny rat species, Tokudaia osimensis and Tokudaia tokunoshimensis (Muridae, Rodentia)

Ryukyu spiny rats (genus Tokudaia) are indigenous species that are confined to three islands of the Nansei Shoto archipelago, Amami-Oshima, Tokunoshima and Okinawa-jima, Japan. Tokudaia tokunoshimensis from Tokunoshima Island and Tokudaia osimensis from Amami-Oshima Island are closely related taxonomically, although their karyotypes are quite different: the diploid chromosome numbers and sex chromosome constitution are 2n=45, X0/X0 for T. tokunoshimensis and 2n=25, X0/X0 for T. osimensis. We conducted comparative chromosome painting with chromosome-specific DNA probes of the laboratory mouse (Mus musculus) to molecularly examine the chromosome homology between T. tokunoshimensis and T. osimensis, and deduced a possible ancestral karyotype of Tokudaia species and the process of evolutionary chromosome rearrangements. The proposed ancestral karyotype with the diploid number of 2n=48, XX/XY was similar to the karyotype of T. tokunoshimensis, and the karyotype of T. osimensis would then have been established through at least 14 chromosomal changes, mainly centric fusion and tandem fusion, from the ancestral karyotype. The close karyological relationship between the ancestral karyotypes of Tokudaia and Apodemus also suggests that the chromosomal evolution in the Tokudaia-Apodemus lineage has been very slow and has accelerated only recently in the branch leading to T. osimensis.

Reciprocal chromosome painting between three laboratory rodent species

The laboratory mouse (Mus musculus, 2n = 40), the Chinese hamster (Cricetulus griseus, 2n = 22), and the golden (Syrian) hamster (Mesocricetus auratus, 2n = 44) are common laboratory animals, extensively used in biomedical research. In contrast with the mouse genome, which was sequenced and well characterized, the hamster species has been set aside. We constructed a chromosome paint set for the golden hamster, which for the first time allowed us to perform multidirectional chromosome painting between the golden hamster and the mouse and between the two species of hamster. From these data we constructed a detailed comparative chromosome map of the laboratory mouse and the two hamster species. The golden hamster painting probes revealed 25 autosomal segments in the Chinese hamster and 43 in the mouse. Using the Chinese hamster probes, 23 conserved segments were found in the golden hamster karyotype. The mouse probes revealed 42 conserved autosomal segments in the golden hamster karyotype. The two largest chromosomes of the Chinese hamster (1 and 2) are homologous to seven and five chromosomes of the golden hamster, respectively. The golden hamster karyotype can be transformed into the Chinese hamster karyotype by 15 fusions and 3 fissions. Previous reconstructions of the ancestral murid karyotype proposed diploid numbers from 2n = 52 to 2n = 54. By integrating the new multidirectional chromosome painting data presented here with previous comparative genomics data, we can propose that syntenies to mouse Chrs 6 and 16 were both present and to hypothesize a diploid number of 2n = 48 for the ancestral Murinae/Cricetinae karyotype.

Mouse models of gastrointestinal tumors

The laboratory mouse (Mus musculus) has become one of the best model animal species in biomedical research today because of its abundant genetic/genomic information, and easy mutagenesis using transgenic and gene knockout technology. Genetically engineered mice have become essential tools in both mechanistic studies and drug development. In this article I will review recent topics in gastrointestinal cancer model mice, with emphasis on the results obtained in our laboratory. They include: (i) mouse models for familial adenomatous polyposis (Apc mutant mice; modifier genes of Apc intestinal polyposis; stabilizing beta-catenin mutant mice); (ii) mouse models for colon cancer (mouse models for hereditary non-polyposis colon cancer; additional mutations in Apc mutant mice; models with mutations in other genes; models for colon cancer associated with inflammatory bowel diseases); and (iii) mouse models for gastric cancer.

Molecular evidence that Heligmosomoides polygyrus from laboratory mice and wood mice are separate species

The gastro-intestinal (GI) nematode Heligmosomoides polygyrus is an important experimental model in laboratory mice and a well-studied parasite of wood mice in the field. Despite an extensive literature, the taxonomy of this parasite in different hosts is confused, and it is unclear whether laboratory and field systems represent the same or different Operational Taxonomic Units (OTUs). Molecular analyses reveal high sequence divergence between H. p. bakeri (laboratory) and H. p. polygyrus (field); 3% difference in the ribosomal DNA Internal Transcribed Spacers (ITS) and 8.6% variation in the more rapidly evolving mitochondrial cytochrome c oxidase I (COI) gene. The COI sequence of U.K. H. p. polygyrus is more similar to H. glareoli from voles than to H. p. bakeri, while a single isolate of H. p. polygyrus from Guernsey confirms the extent of genetic variation between H. p. polygyrus populations. Analysis of molecular variance demonstrated that mtCOI sequence variation is associated primarily with groups with distinct ITS2 sequences, and with host identity, but is not partitioned significantly with a single combined taxon H. polygyrus incorporating European and North American isolates. We conclude therefore that the laboratory OTU should be raised to the level of a distinct species, as H. bakeri from the laboratory mouse Mus musculus, and we reject the hypothesis that H. bakeri has diverged from H. polygyrus in the recent past following introduction into America. However, we are unable to reject the hypothesis that H. polygyrus and H. bakeri are sister taxa, and it may be that H. polygyrus is polyphyletic or paraphyletic.

Genetic Engineering of Mice to Test the Oxidative Damage Theory of Aging

The laboratory mouse Mus musculus domesticus provides the best current mammalian models for the genetic analysis of aging. We give a brief overview of the use of transgenic manipulations to test the oxidative damage theory of aging. These manipulations are of two types: The first approach engineers mice that exhibit increased sensitivities to oxidative damage and thus produces mice that are likely to be short-lived. The second approach engineers mice to be more resistant to such injuries, and thus may produce mice that exhibit enhanced longevities, something that is much harder to engineer. The latter result is thus more meaningful, with the caveat that it may result from some special vulnerability of a particular lab strain or lab strains in general. The first approach, most elegantly carried out by Arlan Richardson's laboratory, provides evidence against the oxidative damage theory. My colleagues and I have been engaged in the second approach and have accumulated evidence supporting the theory. These conventional transgenic experiments, however, should be supplemented by alternative genetic approaches. One that is surprisingly neglected takes advantage of the pleuripotency of embryonic stem cells and the power of somatic cell genetics. A cautionary note is that interventions that minimize oxidative stress may be complicated by unwanted compromises of physiologically adaptive actions such as superoxide signaling and the possible protective effects of certain oxidatively modified proteins.

Regional variations in the distributions of small intestinal intraepithelial lymphocytes (IELs) in outbred laboratory mice ( Mus musculus domesticus) and the inbred strain of mice established from Japanese fancy mice ( Mus musculus molossinus)

Previously, we reported regional variations in small intestinal IELs of mice. In this study, we examined the regional variations of IELs in outbred laboratory mice (ddY: Mus musculus domesticus) and the inbred strain of mice established from Japanese fancy mice (JF1: Mus musculus molossinus). IELs were isolated from the proximal, middle and distal parts of the small intestine and analyzed by flow cytometry. The percentages of γδ T cells and αβ T cell subset of extrathymic origin were higher in the proximal part while the percentages of αβ T cell subset(s) of thymic origin were higher in the distal part in both ddY and JF1 mice. Such trends in regional variations of IELs were almost the same as those found in the inbred strains of laboratory mice in our previous reports. This strongly suggests that these regional variations of IELs may be common phenomena in Mus musculus species.

Mouse behavioural analysis in systems biology

Molecular techniques allowing in vivo modulation of gene expression have provided unique opportunities and challenges for behavioural studies aimed at understanding the function of particular genes or biological systems under physiological or pathological conditions. Although various animal models are available, the laboratory mouse (Mus musculus) has unique features and is therefore a preferred animal model. The mouse shares a remarkable genetic resemblance and aspects of behaviour with humans. In this review, first we describe common mouse models for behavioural analyses. As both genetic and environmental factors influence behavioural performance and need to be carefully evaluated in behavioural experiments, considerations for designing and interpretations of these experiments are subsequently discussed. Finally, common behavioural tests used to assess brain function are reviewed, and it is illustrated how behavioural tests are used to increase our understanding of the role of histaminergic neurotransmission in brain function.

Comparative study of sperm chromatin condensation in the excurrent ducts of the laboratory mouse Mus musculus and spinifex hopping mouse Notomys alexis

In most mammals, post-testicular sperm maturation is completed in the caput and corpus epididymides, with storage occurring in the cauda epididymides. However, in the spinifex hopping mouse, Notomys alexis, epididymal sperm transit is rapid and some sperm storage occurs in the distal region of the vas deferens. The aim of the present study was to determine whether the rapid progression of sperm into the vas deferens in the hopping mouse results in late sperm maturation. To determine this, sperm nuclei from the epididymides and vasa deferentia of laboratory and hopping mice were compared for: (1) thiol content after staining with monobromobimane (mBBr); (2) chromatin resistance to acid denaturation following incubation with acetic alcohol and staining with acridine orange; and (3) chromatin resistance to in vitro decondensation after incubation with 1% sodium dodecyl sulfate (SDS). It was found that, whereas laboratory mouse sperm completed chromatin condensation by the time they reached the cauda epididymidis, hopping mouse sperm nuclei from the vas deferens showed significantly less mBBr fluorescence and a greater proportion of sperm were resistant to decondensation with SDS than those in the cauda epididymidis. Therefore, the results of the present study indicate that, unlike in the laboratory mouse, hopping mouse chromatin condensation of spermatozoa continues in the vas deferens and this may be due, at least in part, to rapid epididymal transit.

Is there a germ plasm in mouse oocytes?

It was found that in the Graafian oocytes of laboratory mice Mus musculus the population of electron-dense bodies contains two patterns of structures. One of these, designated as cortical granules, originated from the Golgi complex and was surrounded by a membrane. The other was discovered as cristae-containing mitochondrial derivatives lacked an outer membrane. It was found that the mitochondrial derivatives underwent progressive condensation and transformed into electron-dense bodies similar to germinal bodies of metazoan animals. Based on examination of Graafian follicle oocytes from 5 female individuals, about 15% of electron-dense bodies were cortical granules. However, about 85% of electron-dense bodies were condensing mitochondrial derivatives transforming into electron-dense bodies.

The relationships between litter size, offspring weight, and behavioral development in laboratory mice Mus musculus

The relationships between litter size, offspring weight, and behavioral development were investigated in 924 offspring from 74 litters of CD-1 control mice. The litters were measured for litter size and offspring weight on postnatal days (PND) 0, 4, 7, 14, and 21 during the lactation period. The offspring were examined for behavioral development including surface righting, negative geotaxis, cliff avoidance, swimming behavior, and olfactory orientation. Offspring weight decreased as litter size increased at PNDs 4, 7, 14, and 21 in both sexes, and the coefficients of determination (r2) of the regression analysis were more than 0.5 and significant (P < 0.01) for each sex. The relationships between litter size and behavioral development were assessed using regression analyses, and litter size incurred few significant effects on the behavioral developmental variables (r2 < 0.5 in each case). The relationships between offspring weight and behavioral development were also assessed using regression analyses, and similarly offspring weight showed few significant effects on the behavioral developmental variables (r2 < 0.5 in each case).

Genetic control of susceptibility to bacterial infections in mouse models.

Historically, the laboratory mouse (Mus musculus) has been the experimental model of choice to study pathophysiology of infection with bacterial pathogens, including natural and acquired host defence mechanisms. Inbred mouse strains differ significantly in their degree of susceptibility to infection with various human pathogens such as Mycobacterium, Salmonella, Legionella and many others. Segregation analyses and linkage studies have indicated that some of these differences are under simple genetic control whereas others behave as complex traits. Major advances in genome technologies have greatly facilitated positional cloning of single gene effects. Thus, a number of genes playing a key role in initial susceptibility, progression and outcome of infection have been uncovered and the functional characterization of the encoded proteins has provided new insight into the molecular basis of antimicrobial defences of polymorphonuclear leukocytes, macrophages, as well as T and B lymphocytes. The multigenic control of susceptibility to infection with certain human pathogens is beginning to be characterized by quantitative trait locus mapping in genome wide scans. This review summarizes recent progress on the mapping, cloning and characterization of genes and proteins that affect susceptibility to infection with major intracellular bacterial pathogens.

Bioaccumulation and damaging action of polymetal industrial dust on laboratory mice Mus musculus alba II. Genetic, cell, and metabolic disturbances

An ecologo–toxicological experiment was carried out with laboratory mice Mus musculus alba of the inbred line BALB/c. The experimental animals (male and female) were exposed for 120 days to polymetal industrial dust containing zinc, copper, lead, and cadmium, which was mixed with conventional animal food. Chromosome aberration frequency and pathological changes in hematological indices, oxygen consumption, body temperature, and body weight were studied in the context of heavy metal bioaccumulation and interactions. Samples for analyses were taken on days 15, 40, 60, and 90. An increased frequency of chromosome aberrations (up to 22%), lead-induced anemia, and significant decreases in body temperature were observed. A strong correlation between hemoglobin content and oxygen consumption (O 2/ g h) was established. An increase in hematocrit, accompanied by a loss of body weight after day 60, suggests dehydration resulting from lead and cadmium poisoning.

Mus musculus and Mus spretus homologues of the human telomere-associated protein TIN2

Telomere length is regulated by TRF1, which binds telomeric DNA, and TIN2, which binds TRF1. Laboratory mice ( Mus musculus) have long telomeres, although a related mouse species, Mus spretus, has human-sized telomeres. Because differences in TIN2 might explain these differences in telomere length, we cloned cDNAs encoding murine TIN2s and compared their sequence to that of human TIN2. M. musculus (Mm) and M. spretus TIN2s were >95% identical, but shared only 67% identity with human TIN2. An N-terminal truncation, or N-terminal fragment, of MmTIN2 elongated M. spretus telomeres. These findings suggest that mouse TIN2, like human TIN2, negatively regulates telomere length, and that N-terminal perturbations have dominant-negative effects. Our findings suggest that differences in TIN2 cannot explain the telomere length differences among Homo sapiens, M. musculus, and M. spretus. Nonetheless, M. spretus cells appear be a good system for studying the function of mouse telomere-associated proteins.

Identification of chromosome rearrangements between the laboratory mouse (Mus musculus) and the Indian spiny mouse (Mus platythrix) by comparative FISH analysis.

Comparative chromosome painting was applied to the Indian spiny mouse (Mus platythrix) with mouse (M. musculus) chromosome-specific probes for understanding the process of chromosome rearrangements between the two species. The chromosome locations of the 5S and 18S-28S ribosomal RNA genes and the order of the 119 and Tcp-1 genes in the In(17)2 region of the t-complex were also compared. All the painting probes were successfully hybridized to the Indian spiny mouse chromosomes, and a total of 27 segments homologous to mouse chromosomes were identified. The comparative FISH analysis revealed that tandem fusions were major events in the chromosome evolution of the Indian spiny mouse. In addition, other types of chromosome rearrangements, i.e. reciprocal translocations and insertions, were also included.

Effects of intestinal nematodes during lactation: consequences for host morphology, physiology and offspring mass.

Sublethal parasites are often assumed to have no detrimental effects on their host. However, the sublethal intestinal nematode Heligmosomoides polygyrus affects both the morphology and the physiology of its laboratory mouse (Mus musculus) host and therefore has the potential to affect host life history. The objectives of the present study were to determine (1) whether lactating and non-lactating mice responded similarly to experimental infection with H. polygyrus and (2) whether the changes in morphology and physiology that occurred with parasite infection affected host reproductive performance. Parasitized mice had greater whole body mass as a result of greater lean mass compared with unparasitized mice. Parasitized mice had larger organs (spleen, stomach, cecum and small intestine) and a diminished rate of glucose transport by the small intestine compared with unparasitized mice. Lactating mice had larger organs (liver, kidney, spleen, heart, stomach, large intestine, cecum and small intestine), lean mass and whole body mass, but a similar rate of glucose transport compared with virgin mice. Resting metabolism increased with lactation but not with parasitism. Lactating and non-lactating mice responded similarly to parasite infection for most measured variables. Production of large litters was followed by production of small litters for parasitized but not unparasitized females. After adjusting for parity and litter size, parasitized mothers produced female pups that were 6% smaller at weaning than female pups from unparasitized mothers, but there was no effect of maternal parasite infection on mass at weaning for male pups. Other measures of reproductive output were not affected by parasite infection.

Maternal and direct effects of the intestinal nematode Heligmosomoides polygyrus on offspring growth and susceptibility to infection.

The laboratory mouse (Mus musculus) has a naturally occurring intestinal nematode (Heligmosomoides polygyrus) that induces an immune response, causes phenotypic plasticity in metabolism and in organ structure and function, and results in changes in host reproductive output. The objectives of the present study were to determine (1) whether pups infected with parasites at weaning grew differently and had a different body composition at adulthood compared with uninfected pups, (2) whether offspring from parasitized mothers grew differently and had a different body composition at adulthood compared with offspring from unparasitized mothers, (3) whether parasite effects on body composition of pups varied under different infection intensities and (4) whether maternal parasite infection affected susceptibility, duration and intensity of offspring parasite infection. H. polygyrus had direct and maternal effects on offspring growth, but final adult mass was not affected by parasites. Parasite infection in offspring had no effect on overall fat mass, but mass changes for some organs were greater for mice that had a high infection intensity compared with mice that had a low infection intensity. Only offspring from parasitized mothers cleared their parasite infection; however, if the infection was not cleared, the final infection intensity was greater for offspring born to parasitized mothers than to unparasitized mothers. This study shows that chronic, sublethal parasite infection with H. polygyrus has both maternal and direct effects that induce physiological changes in growing mice sufficient to alter host growth trajectories, morphology and susceptibility to parasite infection.

The Murine α-Proteinase Inhibitor Gene Family: Polymorphism, Chromosomal Location, and Structure

α1-Proteinase inhibitor (α1-PI) is a member of the serpin superfamily of serine proteinase inhibitors, which function in maintaining homeostasis through regulation of numerous proteolytic processes. In laboratory mice (Mus musculus domesticus), α1-PI occurs in multiple isoforms encoded by a family of three to five genes that are polymorphic among inbred strains and that are located at the Serpina1 locus on chromosome 12. In the present study, we have characterized the α1-PI gene family of inbred mice in more detail. We show that mice express seven isoforms, all of which are encoded by genes that map to the Serpina1 locus. In addition, polymorphism at the locus is defined by three haplotypes (Serpina1b, Serpina1c, and Serpina1l) that differ with regard to both the number and identity of α1-PI genes. Finally, we present the complete sequence of an 84-kb region of Serpina1 containing a tandem repeat of two α1-PI genes.

The Murine α 1-Proteinase Inhibitor Gene Family: Polymorphism, Chromosomal Location, and Structure

α 1-Proteinase inhibitor (α 1-PI) is a member of the serpin superfamily of serine proteinase inhibitors, which function in maintaining homeostasis through regulation of numerous proteolytic processes. In laboratory mice ( Mus musculus domesticus), α 1-PI occurs in multiple isoforms encoded by a family of three to five genes that are polymorphic among inbred strains and that are located at the Serpina1 locus on chromosome 12. In the present study, we have characterized the α 1-PI gene family of inbred mice in more detail. We show that mice express seven isoforms, all of which are encoded by genes that map to the Serpina1 locus. In addition, polymorphism at the locus is defined by three haplotypes ( Serpina1 b , Serpina1 c , and Serpina1 l ) that differ with regard to both the number and identity of α 1-PI genes. Finally, we present the complete sequence of an 84-kb region of Serpina1 containing a tandem repeat of two α 1-PI genes.

Headfirst Ingestion of Prey by Rattlesnakes: Are Tactile Cues Used?

Most vertebrates swallow prey headfirst (e.g., Bolles, 1890; Ewer, 1968; Eisenberg and Leyhausen, 1972; Tinbergen, 1972). This tendency for headfirst ingestion has been observed frequently for adult (Diefenbach and Emslie, 1971; Loop and Bailey, 1972; Greene, 1976; Mori 1996) and neonate snakes (Klein and Loop, 1975; but see Mori, 1994). Probability of headfirst ingestion appears related to prey/predator size ratios and possibly the type of prey (Loop and Bailey, 1972; Franz, 1977; Mori, 1991, 1994, 1996). Potential advantages for headfirst ingestion include a decrease in both swallowing time and probability of incurring injury while handling prey (Greene, 1976). Yet, headfirst ingestion has been observed for prey types for which these benefits are not evident (de Queiroz and de Queiroz, 1987). In such cases, there are presumably no costs associated with headfirst relative to tailfirst ingestion. How do snakes locate the head of their prey to begin ingestion? Tactile cues appear to play a role. For instance, Greene (1976) found that snakes feeding on other snakes used scale overlap as a directional cue to locate the head. Mori (1998) found a similar result for piscivorous snakes. For snakes feeding on mammals, the direction of the hair has been suggested as a stimulus for locating the head (Diefenbach and Emslie, 1971). Chemical and visual cues, such as body shape, may also be used for head location (Naulleau, 1966; Diefenbach and Emslie, 1971; Greene, 1976). The objective of my study was to test whether rattlesnakes use tactile cues, specifically hair, to locate the head of their prey for ingestion. I report both qualitative observations and quantitative statistical tests comparing rattlesnakes feeding on mice with and without hair. By comparing these results with previous studies, I suggest that the type of cues used to locate the head of prey varies based on the feeding behavior of snakes. Subjects were eight Crotalus viridis collected from several populations throughout the range of this species. All subjects were long-term laboratory residents (> 2 yr) and were individually housed in aquariums 52 cm x 36 cm x 20 cm with water available ad libitum. Snakes were maintained on a 12:12 L:D cycle with access to radiant heat during the light part of the cycle. All snakes were fed laboratory mice (Mus musculus) prior to the initiation of this experiment. Two types of laboratory mice were used for these experiments: regular lab mice (hair present), and lab mice that were devoid of hair (hair absent). The latter