Breeding Of Mice Research Articles

Dendritic Morphology of Hippocampal and Amygdalar Neurons in Adolescent Mice Is Resilient to Genetic Differences in Stress Reactivity

Many studies have shown that chronic stress or corticosterone over-exposure in rodents leads to extensive dendritic remodeling, particularly of principal neurons in the CA3 hippocampal area and the basolateral amygdala. We here investigated to what extent genetic predisposition of mice to high versus low stress reactivity, achieved through selective breeding of CD-1 mice, is also associated with structural plasticity in Golgi-stained neurons. Earlier, it was shown that the highly stress reactive (HR) compared to the intermediate (IR) and low (LR) stress reactive mice line presents a phenotype, with respect to neuroendocrine parameters, sleep architecture, emotional behavior and cognition, that recapitulates some of the features observed in patients suffering from major depression. In late adolescent males of the HR, IR, and LR mouse lines, we observed no significant differences in total dendritic length, number of branch points and branch tips, summated tip order, number of primary dendrites or dendritic complexity of either CA3 pyramidal neurons (apical as well as basal dendrites) or principal neurons in the basolateral amygdala. Apical dendrites of CA1 pyramidal neurons were also unaffected by the differences in stress reactivity of the animals; marginally higher length and complexity of the basal dendrites were found in LR compared to IR but not HR mice. In the same CA1 pyramidal neurons, spine density of distal apical tertiary dendrites was significantly higher in LR compared to IR or HR animals. We tentatively conclude that the dendritic complexity of principal hippocampal and amygdala neurons is remarkably stable in the light of a genetic predisposition to high versus low stress reactivity, while spine density seems more plastic. The latter possibly contributes to the behavioral phenotype of LR versus HR animals.

What have we learned from brucellosis in the mouse model?

Brucellosis is a zoonosis caused by Brucella species. Brucellosis research in natural hosts is often precluded by practical, economical and ethical reasons and mice are widely used. However, mice are not natural Brucella hosts and the course of murine brucellosis depends on bacterial strain virulence, dose and inoculation route as well as breed, genetic background, age, sex and physiological statu of mice. Therefore, meaningful experiments require a definition of these variables. Brucella spleen replication profiles are highly reproducible and course in four phases: i), onset or spleen colonization (first 48 h); ii), acute phase, from the third day to the time when bacteria reach maximal numbers; iii), chronic steady phase, where bacterial numbers plateaus; and iv), chronic declining phase, during which brucellae are eliminated. This pattern displays clear physiopathological signs and is sensitive to small virulence variations, making possible to assess attenuation when fully virulent bacteria are used as controls. Similarly, immunity studies using mice with known defects are possible. Mutations affecting INF-γ, TLR9, Myd88, Tγδ and TNF-β favor Brucella replication; whereas IL-1β, IL-18, TLR4, TLR5, TLR2, NOD1, NOD2, GM-CSF, IL/17r, Rip2, TRIF, NK or Nramp1 deficiencies have no noticeable effects. Splenomegaly development is also useful: it correlates with IFN-γ and IL-12 levels and with Brucella strain virulence. The genetic background is also important: Brucella-resistant mice (C57BL) yield lower splenic bacterial replication and less splenomegaly than susceptible breeds. When inoculum is increased, a saturating dose above which bacterial numbers per organ do not augment, is reached. Unlike many gram-negative bacteria, lethal doses are large (≥ 108 bacteria/mouse) and normally higher than the saturating dose. Persistence is a useful virulence/attenuation index and is used in vaccine (Residual Virulence) quality control. Vaccine candidates are also often tested in mice by determining splenic Brucella numbers after challenging with appropriate virulent brucellae doses at precise post-vaccination times. Since most live or killed Brucella vaccines provide some protection in mice, controls immunized with reference vaccines (S19 or Rev1) are critical. Finally, mice have been successfully used to evaluate brucellosis therapies. It is concluded that, when used properly, the mouse is a valuable brucellosis model.

Selective breeding of mice for high voluntary exercise alters adaptive plasticity of metabolic phenotypes in skeletal muscle

The response to selection on behavior necessarily entails associated changes in lower‐level (subordinate) traits. We studied mice from 4 replicate lines that had been selectively bred for high levels of voluntary exercise (High Runner or HR) that run ~3‐fold more wheel revolutions/day than those from 4 non‐selected control (C) lines, and have evolved higher baseline endurance and VO2max. We examined hindlimb skeletal muscle metabolic capacity in mice housed with or without wheel access for 8 weeks. Triceps surae muscles were assayed at 37C for Vmax of hexokinase (HK), citrate synthase (CS), carnitine palmitoyl‐transferase (CPT), and β‐hydroxyacyl‐CoA dehydrogenase (HAD). Wheel access increased heart ventricle mass in both HR and C lines, but only HR showed increased enzyme activities as well as higher phosphorylation of 5ˈ‐AMP‐activated protein kinase. Analysis of wheel‐access groups indicated the greater training effect in HR could be explained statistically by their greater wheel running for ventricle mass, CS, and HAD, but for HK and CPT, HR mice had greater adaptive plasticity of the response to voluntary exercise. Thus, HR do not have inherent baseline differences in metabolic capacity, but they have evolved greater adaptive plasticity for some traits. Supported by NSF IOB‐0543429 and IOS‐1121273 to TG.

Decreased expression of Wnt9b and Ube2ql1 in the face of CL/Fr mouse embryos at E11.5 based on microarray analysis

The CL/Fr mouse demonstrates heritable bilateral and unilateral cleft lip and palate (CLP) at a rate of approximately 35%, generally above the background “A” strain mouse. Using classical mouse breeding strategies, it has been suggested that at least two disease loci, clf1 and clf2, are involved in the defect and candidate genes have been identified. Additionally, gene‐targeting analyses strongly suggest that Wnt9b contributes to CLP in the “A” strain mice. The aim of this study was to test the expression of clf1 and clf2 candidate genes in the facial prominences of CL/Fr embryos, utilizing microarray analysis. Medial nasal, lateral nasal, and maxillary prominences of phenotypically normal as well as cleft E11.5 CL/Fr mice were dissected and RNA was extracted using standard techniques for Agilent‐microarray protocol. Results indicate that expression of the clf1 candidate gene, Wnt9b, and the clf2 candidate gene, Ube2ql1, are significantly reduced (−3.11 and −1.83 fold, respectively) in the CL/Fr cleft tissues, suggesting these genes may be involved in the CLP mutation in CL/Fr mice. Future gene expression studies through quantitative RT‐PCR and regional expression analyses through immunohistochemistry and whole mount in situ hybridization will be performed to further test the expression of these clf1 and clf2 candidate genes.Grant Funding Source: NIH/NCRR 5P20RR024206 (S.J.S) and R01‐DK‐064752 (SL)

Life History Features and Aging Rates: Insights from Intra-specific Patterns in the Cricket Acheta domesticus

We carried out 42 lifetime studies of male and female crickets (Acheta domesticus) treated with different diets, nutritional supplements and dietary restriction (84 groups). Maximal longevity of controls averaged ~118 days and various treatments obtained lifespans of 86–257 days. Overall, greater longevity was most strongly associated with slower growth and delayed maturation. Early nymphal mortality and early fasting stress were also associated with life extension. The opposite associations of growth rate and stress resistance with maximal life span are consistent with modulation of aging by the target of rapamycin (growth) and forkhead transcription factors (stress resistance). Unlike inter-specific comparisons or intra-specific comparisons of species differentiated into strains or breeds, body size did not emerge as a strong predictor of cricket longevity. Rather, targeted body size was strongly compensated for in crickets whereas most genetically differentiated breeds of mice, rats, horses and dogs express breed-specific sizes and growth rates. Both extension of the juvenile period and adult lifetime contributed to increases in maximal longevity of crickets, although for extreme life extension, extended immaturity was a greater factor than adult life span. We discuss the inter- and intra-specific allometry of life histories from a perspective of aging and suggest that inter-specific variance may particularly reflect exogenous mortality risks whereas intra-specific aging is dominated by constraints on productivity.

Japanese Wild Mice: A Rich Resource for New Disease Models

Breeding of fancy mice has been a tradition in Japan. Recent progress in animal science has shed a new light on Japanese wild-derived mice as tools for discovery of new disease models because these mice, Mus musculus molossinus, are genetically far remote from the majority of available laboratory mice. After decades of effort, five inbred strains of mice have been established from pairs of wild mice trapped in Tohoku, northeastern Japan, namely KOR1/Stm, KOR5/Stm, KOR7/Stm, AIZ/Stm, and MAE/Stm. They carried numerous mutations, leading to a variety of diseases. During the inbreeding of KOR1, the first spontaneous mutation was found in the Apoe (apolipoprotein E) gene, and the mutant was later designated as spontaneous hyperlipidemic (SHL). Thereafter, a number of other mutations were discovered among wild-derived inbred strains, including atopic dermatitis, microphthalmia, dominant white spots, sebaceous gland abnormalities, and audible song-like vocalization. Furthermore, to examine the possible effects of the genetic background for these mutant genes, sets of congenic strains were generated, in which the mutant gene was introduced into at least 3 different strains of laboratory mice, including BALB/c and C57BL/6. These congenic strains have now been established as novel disease models. These wild-derived inbred strains serve as a treasure trove for novel disease models. Most of them have been deposited in the Riken BioResource Center (BRC), and some are also available from commercial breeders.

Selective breeding of mice for different susceptibilities to high fat diet-induced glucose intolerance: Development of two novel mouse lines, Selectively bred Diet-induced Glucose intolerance-Prone and -Resistant.

Aims/Introduction: The development of type 2 diabetes is primarily due to lifestyle and environmental factors, as well as genetics, as shown by familial clustering. To establish mouse lines for evaluating heritable factors determining susceptibility to diet-induced diabetes, we performed selective breeding for differences in high fat diet (HFD)-induced glucose intolerance. Selective breeding was performed using hybrid mice of C57BL/6J, C3H/HeJ and AKR/N backgrounds. After 5-week HFD feeding, mice showing high and low 2-h blood glucose levels in an oral glucose tolerance test (OGTT) were selected and bred over 14 generations to produce lines prone and resistant to diet-induced glucose intolerance (designated Selectively bred Diet-induced Glucose intolerance-Prone [SDG-P] and -Resistant [SDG-R]). At 5 weeks of age (pre HFD feeding), SDG-P mice showed higher blood glucose levels both in the OGTT and insulin tolerance test as compared to SDG-R mice. After receiving HFD, the glucose intolerance of SDG-P mice became more evident without hyper insulin secretion. In addition, SDG-P mice had greater body weight gain and lower HDL-cholesterol levels as compared to SDG-R mice. In comparison with C57BL/6J, a well-known strain prone to HFD-induced glucose intolerance, SDG-P mice showed significantly higher glucose levels in OGTT after the 5-week HFD feeding. Susceptibility to HFD-induced glucose intolerance was transmitted over generations and was intensified by selective breeding. The newly established mouse lines, SDG-P and SDG-R, may be useful in investigating the pathophysiology of type 2 diabetes through elucidating the crucial factors for determining the susceptibility to HFD-induced glucose intolerance. (J Diabetes Invest, doi: 10.1111/j.2040-1124.2011.00175.x, 2011).

Control of Megakaryocyte Expansion and Bone Marrow Fibrosis by Lysyl Oxidase

Lysyl oxidase (LOX), a matrix cross-linking protein, is known to be selectively expressed and to enhance a fibrotic phenotype. A recent study of ours showed that LOX oxidizes the PDGF receptor-β (PDGFR-β), leading to amplified downstream signaling. Here, we examined the expression and functions of LOX in megakaryocytes (MKs), the platelet precursors. Cells committed to the MK lineage undergo mitotic proliferation to yield diploid cells, followed by endomitosis and acquisition of polyploidy. Intriguingly, LOX expression is detected in diploid-tetraploid MKs, but scarce in polyploid MKs. PDGFR-BB is an inducer of mitotic proliferation in MKs. LOX inhibition with β-aminopropionitrile reduces PDGFR-BB binding to cells and downstream signaling, as well as its proliferative effect on the MK lineage. Inhibition of LOX activity has no influence on MK polyploidy. We next rationalized that, in a system with an abundance of low ploidy MKs, LOX could be highly expressed and with functional significance. Thus, we resorted to GATA-1(low) mice, where there is an increase in low ploidy MKs, augmented levels of PDGF-BB, and an extensive matrix of fibers. MKs from these mice display high expression of LOX, compared with control mice. Importantly, treatment of GATA-1(low) mice with β-aminopropionitrile significantly improves the bone marrow fibrotic phenotype, and MK number in the spleen. Thus, our in vitro and in vivo data support a novel role for LOX in regulating MK expansion by PDGF-BB and suggest LOX as a new potential therapeutic target for myelofibrosis.

Phenotypes in mTERT+/− and mTERT−/− Mice Are Due to Short Telomeres, Not Telomere-Independent Functions of Telomerase Reverse Transcriptase

Telomerase is essential for telomere length maintenance. Mutations in either of the two core components of telomerase, telomerase RNA (TR) or the catalytic protein component telomerase reverse transcriptase (TERT), cause the genetic disorders dyskeratosis congenita, pulmonary fibrosis, and other degenerative diseases. Overexpression of the TERT protein has been reported to have telomere length-independent roles, including regulation of the Wnt signaling pathway. To examine the phenotypes of TERT haploinsufficiency and determine whether loss of function of TERT has effects other than those associated with telomere shortening, we characterized both mTERT⁺/⁻ and mTERT⁻/⁻ mice on the CAST/EiJ genetic background. Phenotypic analysis showed a loss of tissue renewal capacity with progressive breeding of heterozygous mice that was indistinguishable from that of mTR-deficient mice. mTERT⁻/⁻ mice, from heterozygous mTERT⁺/⁻ mouse crosses, were born at the expected Mendelian ratio (26.5%; n = 1,080 pups), indicating no embryonic lethality of this genotype. We looked for, and failed to find, hallmarks of Wnt deficiency in various adult and embryonic tissues, including those of the lungs, kidneys, brain, and skeleton. Finally, mTERT⁻/⁻ cells showed wild-type levels of Wnt signaling in vitro. Thus, while TERT overexpression in some settings may activate the Wnt pathway, loss of function in a physiological setting has no apparent effects on Wnt signaling. Our results indicate that both TERT and TR are haploinsufficient and that their deficiency leads to telomere shortening, which limits tissue renewal. Our studies imply that hypomorphic loss-of-function alleles of hTERT and hTR should cause a similar disease spectrum in humans.

Genetic association between helpless trait and depression-related phenotypes: evidence from crossbreeding studies with H/Rouen and NH/Rouen mice

Genetic factors are believed to be involved in the aetiology of unipolar depressive disorders. We have previously described a model built up by selective breeding of mice with different responses in the tail suspension test, a screening test for potential antidepressants. In this model, helpless H/Rouen mice are essentially immobile in this test, as well as in the Porsolt forced-swim test, whereas non-helpless NH/Rouen mice show the opposite behaviour, i.e. very low immobility. However, it is unclear whether or not the other phenotypic differences (forced swim test, locomotor activity, sucrose test, sleep patterns, effect of fluoxetine) observed between H/Rouen and the NH/Rouen mice may be attributed to a genetic drift phenomenon during the selection step, rather than being related to the trait of selection. In this study we used reciprocal crossbreeding between H/Rouen and NH/Rouen mice and obtained a segregating F2 population in order to determine whether phenotypic differences between the two lines co-segregate with the trait of selection. In the segregating F2 population, we found significant and strong genetic correlations between helplessness in the tail suspension test and some phenotypical features associated with depressive disorders such as 'alterations of sleep patterns', behavioural response to fluoxetine, immobility duration in the forced swim test, and anhedonia. Our results converge with clinical observations in depressed humans. These results strengthen the validity of the H/Rouen mouse as a model of depression, notably for preclinical studies with antidepressants. In addition, this model should open the way to identifying genes related to depression-like behaviours.

Crucial role of alkaline sphingomyelinase in sphingomyelin digestion: a study on enzyme knockout mice

Alkaline sphingomyelinase (alk-SMase) hydrolyses sphingomyelin (SM) to ceramide in the gut. To evaluate the physiological importance of the enzyme, we generated alk-SMase knockout (KO) mice by the Cre-recombinase-Locus of X-over P1(Cre-LoxP) system and studied SM digestion. Both wild-type (WT) and KO mice were fed ³H-palmitic acid labeled SM together with milk SM by gavage. The lipids in intestinal content, intestinal tissues, serum, and liver were analyzed by TLC. In KO mice, nondigested ³H-SM in the intestinal content increased by 6-fold and the formation of ³H-ceramide decreased markedly, resulting in 98% reduction of ³H-ceramide/³H-SM ratio 1 h after gavage. The absorbed ³H-palmitic acid portion was decreased by 95%. After 3 h, a small increase in ³H-ceramide was identified in distal intestine in KO mice. In feces, ³H-SM was increased by 243% and ceramide decreased by 74% in the KO mice. The KO mice also showed significantly decreased radioactivity in liver and serum. Furthermore, alkaline phosphatase activity in the mucosa was reduced by 50% and histological comparison of two female littermates preliminarily suggested mucosal hypertrophy in KO mice. This study provides definite proof for crucial roles of alk-SMase in SM digestion and points to possible roles in regulating mucosal growth and alkaline phosphatase function.

Mouse Breeding and Colony Management.

The possibility to genetically modify the mouse genome has enabled the creation of numerous lines of genetically engineered mouse models (GEMMs). As a result, the demand for housing space in research facilities is increasing. Knowledge of the basis of mouse reproduction and of the methods to handle colonies of GEMMs is therefore mandatory to efficiently populate facilities. The mouse has a short generation period, produces large progenies, and can breed all year round. However, environmental parameters (bedding, diet, cage type, temperature, hygrometry, light, noise, and sanitary status) strongly influence the breeding efficiency and experimental data, and must be tightly controlled. Efficient GEMM colony management requires adequate recording of breeding and proper identification and genotyping of animals. Various mating types and breeding schemes can be used, depending on the type of studies conducted. The recent development of assisted reproduction methods helps circumvent some of the issues faced with those lines especially difficult to breed. Curr. Protoc. Mouse Biol. 1:239-264. © 2011 by John Wiley & Sons, Inc.

An immunohistochemical study on the localization of type II collagen in the developing mouse mandibular condyle

The present chronological investigation assessed the distribution of type II collagen expression in the developing mouse mandibular condyle using immunohistochemical staining with respect to the anatomy of the anlage of the mandibular condyle, the histological characteristics of which were disclosed in our previous investigation. We analyzed fetuses, obtained by cross breeding of ICR strain mice, between 14.0 and 19.0 days post-conception (dpc) and pups on 1, 3, and 5 days post-natal (dpn) using immunohistochemical staining with 2 anti-type II collagen antibodies. The expression of type II collagen was first detected at 15.0 dpc in the lower part of the hypertrophic chondrocyte zone; thereafter, this type II collagen-positive layer was expanded and intensified (P1 layer). At 17.0 dpc, we identified a type II collagen-negative layer (N layer) around the P1 layer and we also identified another newly formed type II collagen-positive layer (P, layer) on the outer surface of the N layer. The most typical and conspicuous 3-layered distribution was observed at 1 dpn; thereafter, there was a reduction in the intensity of expression, and with it, the demarcation between the layers was weakened by 5 dpn. The P1 layer was derived from the central region of the core cell aggregate of the anlage of the mandibular condyle and participated in endochondral bone formation. The N layer was derived from the fringe of the core cell aggregate of the anlage, formed the bone collar at the side of the condyle by intramembranous bone formation, and showed a high level of proliferative activity at the vault. The P2 layer was formed from the outgrowth of the N layer, and could be considered as the secondary cartilage. The intensive expression of type II collagen from 17.0 dpc to 3 dpn was detected in the fibrous sheath covering the condylar head, which is derived from the peripheral cell aggregate of the anlage. Since its expression in the fibrous sheath was not detected in the neighboring section in the absence of hyaluronidase digestion, some changes in the extracellular matrix of the fibrous sheath appear to participate in the generation of the lower joint space. The results of the present investigation indicate that further studies are required to fully characterize the development of the mouse mandibular condyle.

Lasker Lauds Leptin

This year, the Albert Lasker Basic Medical Research Award will be shared by Douglas Coleman and Jeffrey Friedman for their discovery of leptin, a hormone that regulates appetite and body weight. By uncovering a critical physiologic system, their discovery markedly accelerated our capacity to apply molecular and genetic techniques to understand obesity.

Early autophagic response in a novel knock-in model of Huntington disease

The aggregation of mutant polyglutamine (polyQ) proteins has sparked interest in the role of protein quality-control pathways in Huntington's disease (HD) and related polyQ disorders. Employing a novel knock-in HD mouse model, we provide in vivo evidence of early, sustained alterations of autophagy in response to mutant huntingtin (mhtt). The HdhQ200 knock-in model, derived from the selective breeding of HdhQ150 knock-in mice, manifests an accelerated and more robust phenotype than the parent line. Heterozygous HdhQ200 mice accumulate htt aggregates as cytoplasmic aggregation foci (AF) as early as 9 weeks of age and striatal neuronal intranuclear inclusions (NIIs) by 20 weeks. By 40 weeks, striatal AF are perinuclear and immunoreactive for ubiquitin and the autophagosome marker LC3. Striatal NIIs accumulate earlier in HdhQ200 mice than in HdhQ150 mice. The earlier appearance of aggregate pathology in HdhQ200 mice is paralleled by earlier and more rapidly progressive motor deficits: progressive imbalance and decreased motor coordination by 50 weeks, gait deficits by 60 weeks and gross motor impairment by 80 weeks of age. At 80 weeks, heterozygous HdhQ200 mice exhibit striatal and cortical astrogliosis and a approximately 50% reduction in striatal dopamine receptor binding. Increased LC3-II protein expression, which is noted early and sustained throughout the disease course, is paralleled by increased expression of the autophagy-related protein, p62. Early and sustained expression of autophagy-related proteins in this genetically precise mouse model of HD suggests that the alteration of autophagic flux is an important and early component of the neuronal response to mhtt.

Cathepsin H Is an Additional Convertase of Pro-granzyme B

The serine protease granzyme B (GrB) is the most potent proapoptotic cytotoxin of the granule exocytosis pathway of cytotoxic lymphocytes. GrB is synthesized as a zymogen (proGrB) and activated in cytotoxic granules by the lysosomal cysteine protease cathepsin C (CatC) which removes the N-terminal dipeptide Gly-Glu. It has been shown recently that mice lacking CatC nonetheless express significant residual GrB activity, indicating the presence of additional proGrB convertases. Here, we describe an assay to assess activation of proGrB and show that the amino-peptidase cathepsin H (CatH) has proGrB convertase activity in vitro, whereas dipeptidylpeptidase II does not. We generated mice lacking both CatC and CatH expression (CatCH(-/-)) and found that their lymphocytes have reduced convertase activity compared with those from CatC-deficient mice. Despite this, cytotoxic lymphocytes from CatCH(-/-) mice retain cytotoxic activity and some residual GrB activity. We conclude that CatH can act as an additional proGrB convertase and that other protease/s (apart from dipeptidylpeptidase II) must also possess convertase activity. This indicates a great deal of functional redundancy in GrB maturation, which would prevent pathogen-mediated immune suppression by via convertase inhibition.

Seasonal breeding in relation to dietary animal protein in deer mice (Peromyscus maniculatus)

We used stable carbon and nitrogen isotope compositions of hair and liver as a way of examining seasonal diet changes and explaining seasonal breeding in deer mice ( Peromyscus maniculatus (Wagner, 1845)). Summer and winter δ13C values differed, which is attributed to the availability of different plant tissues (C3 plants). The δ15N values of liver showed a decrease in consumed animal protein during winter, but the difference was not large enough to indicate a full trophic level change in diet from summer to winter. The δ15N values of hair remained constant across the seasons, which is attributed to a continuous level of moulting throughout the year. Our data indicate that lowered food quality in the form of reduced dietary animal protein intake may play a role in the cessation of breeding in deer mice in winter.

Genes, Physiology, Behavior All Linked in One Study

Although it is not possible to test whether a mouse is psychotic, it is possible to measure the mouse's impairment in working memory; this is analogous to a cognitive deficit observed in human patients with schizophrenia. In this study, mice were trained in a spatial task, which required them to retrieve recently learned information. First, a mouse was directed to turn in one of two possible directions in a T-shaped maze. Next, the animals had to remember which direction they took before and turn in the opposite direction to find food. Thus, how quickly a mouse learned to perform the task is a measurement of its working memory.

Altered myosin heavy chain phenotype in locomotor and non‐locomotor muscles of mini‐muscle mice bred for high running capacity

Replicated selective breeding of mice for high voluntary wheel running for over 50 generations resulted in four lines of mice that display a high‐running phenotype. Individuals in two of the four lines display a smaller hindlimb muscle mass (mini‐muscle mice), inherited as a Mendelian recessive. In one line (lab designation line 3), all mice now have the mini‐muscle phenotype. Previous studies suggested that mini‐muscle mice also have differences in myosin heavy chain (MyHC) isoform content in hindlimb muscles. This study evaluated whether the changes in MyHC content were restricted to locomotor muscles. Electrophoretic analyses revealed that both locomotor (vastus lateralis, trapezius) and non‐locomotor (lingual) muscles of mini‐muscle mice had greatly reduced 2b MyHC isoform content compared to control mice. The loss in 2b MyHC isoform content in the mini‐muscle mice was compensated by a corresponding increase in 2a and 2x MyHC isoforms. The data suggest that alterations in the MyHC isoform profile in mini‐muscle mice are not restricted to locomotor muscles. Thus, the underlying gene appears to have a general influence on specifying muscle phenotype. NSF IOB‐0543429 to T.G.

Prevalence of Laboratory Animal Allergy in Laboratory Workers

This study was designed to analyze the prevalence rates of laboratory animal allergy (LAA) in laboratory workers who perform researches with animals, and detect the mouse urinary allergen (Mus m 1) level in animal facilities for the purpose of establishing program for prevention of exposure to allergen. Study subjects were 240 employees who were working for two animal research institutions in Korea. Then the questionnaire and skin prick tests (SPTs) using twenty allergens were conducted with them. Presence of Mus m 1 in each air borne sample collected from animal facility was determined by using enzyme-linked immunosorbent assay. Through 240 questionnaire sheets, we found that; (1) 17.0% of workers in the direct exposure group answered that they had allergic symptoms due to laboratory animals; and (2) 6.2% of them had asthmatic symptoms. Twenty one subjects (27.6%) among the subjects with common allergens positive result and five subjects (6.6%) among the subjects with negative result showed a positive response to LAA under the SPTs. The Mus m 1 concentration (1.339 ng/㎥) in the sample collected during cage exchange in mouse breeding room was up to 2.8 times higher than its concentration (0.483 ng/㎥) in the sample collected at the stationary state. We suggest that LAA management programs including control of exposure to laboratory animal allergens should be considered as a measure to reduce the incidence of LAA and relieve the laboratory worker’s allergic sensitivity to laboratory animals.