Common Inbred Mouse Strains Research Articles

Sex differences in avoidance behavior and cued threat memory dynamics in mice: Interactions between estrous cycle and genetic background

Anxiety disorders are the most prevalent mental illnesses worldwide, exhibit high heritability, and affect twice as many women as men. To evaluate potential interactions between genetic background and cycling ovarian hormones on sex differences in susceptibility to negative valence behaviors relevant to anxiety disorders, we assayed avoidance behavior and cued threat memory dynamics in gonadally-intact adult male and female mice across four common inbred mouse strains: C57Bl/6J, 129S1/SVlmJ, DBA/2J, and BALB/cJ. Independent of sex, C57Bl/6J mice exhibited low avoidance but high threat memory, 129S1/SvlmJ mice high avoidance and high threat memory, DBA/2J mice low avoidance and low threat memory, and BALB/cJ mice high avoidance but low threat memory. Within-strain comparisons revealed reduced avoidance behavior in the high hormone phase of the estrous cycle (proestrus) compared to all other estrous phases in all strains except DBA/2J, which did not exhibit cycle-dependent behavioral fluctuations. Robust and opposing sex differences in threat conditioning and extinction training were found in the C57Bl/6J and 129S1/SvlmJ lines, whereas no sex differences were observed in the DBA/2J or BALB/cJ lines. C57Bl/6J males exhibited enhanced acute threat memory, whereas 129S1/SvlmJ females exhibited enhanced sustained threat memory, compared to their sex-matched littermates. These effects were not mediated by estrous cycle stage or sex differences in active versus passive defensive behavioral responses. Our data demonstrate that core features of behavioral endophenotypes relevant to anxiety disorders, such as avoidance and threat memory, are genetically driven yet dissociable and can be influenced further by cycling ovarian hormones.

Comparison of three common inbred mouse strains reveals substantial differences in hippocampal GABAergic interneuron populations and in vitro network oscillations.

A major challenge in neuroscience is to pinpoint neurobiological correlates of specific cognitive and neuropsychiatric traits. At the mesoscopic level, promising candidates for establishing such connections are brain oscillations that can be robustly recorded as local field potentials with varying frequencies in the hippocampus in vivo and in vitro. Inbred mouse strains show natural variation in hippocampal synaptic plasticity (e.g. long-term potentiation), a cellular correlate of learning and memory. However, their diversity in expression of different types of hippocampal network oscillations has not been fully explored. Here, we investigated hippocampal network oscillations in three widely used inbred mouse strains: C57BL/6J (B6J), C57BL/6NCrl (B6N) and 129S2/SvPasCrl (129) with the aim to identify common oscillatory characteristics in inbred mouse strains that show aberrant emotional/cognitive behaviour (B6N and 129) and compare them to "control" B6J strain. First, we detected higher gamma oscillation power in the hippocampal CA3 of both B6N and 129 strains. Second, higher incidence of hippocampal sharp wave-ripple (SPW-R) transients was evident in these strains. Third, we observed prominent differences in the densities of distinct interneuron types and CA3 associative network activity, which are indispensable for sustainment of mesoscopic network oscillations. Together, these results add further evidence to profound physiological differences among inbred mouse strains commonly used in neuroscience research.

Mouse strain-dependent variation in metabolic associated fatty liver disease (MAFLD): a comprehensive resource tool for pre-clinical studies

Non-alcoholic steatohepatitis (NASH), characterized as the joint presence of steatosis, hepatocellular ballooning and lobular inflammation, and liver fibrosis are strong contributors to liver-related and overall mortality. Despite the high global prevalence of NASH and the substantial healthcare burden, there are currently no FDA-approved therapies for preventing or reversing NASH and/or liver fibrosis. Importantly, despite nearly 200 pharmacotherapies in different phases of pre-clinical and clinical assessment, most therapeutic approaches that succeed from pre-clinical rodent models to the clinical stage fail in subsequent Phase I-III trials. In this respect, one major weakness is the lack of adequate mouse models of NASH that also show metabolic comorbidities commonly observed in NASH patients, including obesity, type 2 diabetes and dyslipidaemia. This study provides an in-depth comparison of NASH pathology and deep metabolic profiling in eight common inbred mouse strains (A/J, BALB/c, C3H/HeJ, C57BL/6J, CBA/CaH, DBA/2J, FVB/N and NOD/ShiLtJ) fed a western-style diet enriched in fat, sucrose, fructose and cholesterol for eight months. Combined analysis of histopathology and hepatic lipid metabolism, as well as measures of obesity, glycaemic control and insulin sensitivity, dyslipidaemia, adipose tissue lipolysis, systemic inflammation and whole-body energy metabolism points to the FVB/N mouse strain as the most adequate diet-induced mouse model for the recapitulation of metabolic (dysfunction) associated fatty liver disease (MAFLD) and NASH. With efforts in the pharmaceutical industry now focussed on developing multi-faceted therapies; that is, therapies that improve NASH and/or liver fibrosis, and concomitantly treat other metabolic comorbidities, this mouse model is ideally suited for such pre-clinical use.

Two Loci Contribute to Age-Related Hearing Loss Resistance in the Japanese Wild-Derived Inbred MSM/Ms Mice

An MSM/Ms strain was established using Japanese wild mice, which exhibit resistance to several phenotypes associated with aging, such as obesity, inflammation, and tumorigenesis, compared to common inbred mouse strains. MSM/Ms strain is resistant to age-related hearing loss, and their auditory abilities are sustained for long durations. The age-related hearing loss 3 (ahl3) locus contributes to age-related hearing in MSM/Ms strain. We generated ahl3 congenic strains by transferring a genomic region on chromosome 17 from MSM/Ms mice into C57BL/6J mice. Although C57BL/6J mice develop age-related hearing loss because of the ahl allele of the cadherin 23 gene, the development of middle- to high-frequency hearing loss was significantly delayed in an ahl3 congenic strain. Moreover, the novel age-related hearing loss 10 (ahl10) locus associated with age-related hearing resistance in MSM/Ms strain was mapped to chromosome 12. Although the resistance effects in ahl10 congenic strain were slightly weaker than those in ahl3 congenic strain, slow progression of age-related hearing loss was confirmed in ahl10 congenic strain despite harboring the ahl allele of cadherin 23. These results suggest that causative genes and polymorphisms of the ahl3 and ahl10 loci are important targets for the prevention and treatment of age-related hearing loss.

ICLAS LAQ Network for the Promotion of Animal Quality in Research.

ICLAS Laboratory Animal Quality Network (LAQN) programs currently consist of the Performance Evaluation Program (PEP), which focuses on microbial monitoring by and for laboratory animal diagnostic laboratories, and the Genetic Reference Monitoring Program (GENRef), which provides assay-ready reference DNA for genetic testing of mouse strains. Since 2008, PEP has grown to become a truly international program with participating laboratories in 5 continents. Launched in 2016, GENRef currently distributes DNA from 12 common inbred mouse strains for use in genetic monitoring of locally inbred colonies as well as for genetic testing of stocks, particularly genetically engineered stocks, of uncertain origins. GENRef has the capacity to include additional strains as well as additional species. PEP and GENRef provide the reagents at cost, as a resource to the international scientific community, in the interest of improving research quality in an environment of growing concern for research quality, rigor, and reproducibility.

Identification of Basp1 as a novel angiogenesis-regulating gene by multi-model system studies.

We have previously used the genetic diversity available in common inbred mouse strains to identify quantitative trait loci (QTLs) responsible for the differences in angiogenic response using the corneal micropocket neovascularization (CoNV) assay. Employing a mouse genome-wide association study (GWAS) approach, the region on chromosome 15 containing Basp1 was identified as being significantly associated with angiogenesis in inbred strains. Here, we developed a unique strategy to determine and verify the role of BASP1 in angiogenic pathways. Basp1 expression in cornea had a strong correlation with a haplotype shared by mouse strains with varied angiogenic phenotypes. In addition, inhibition of BASP1 demonstrated a dosage-dependent effect in both primary mouse brain endothelial and human microvascular endothelial cell (HMVEC) migration. To investigate its role in vivo, we knocked out basp1 in transgenic kdrl:zsGreen zebrafish embryos using a widely adopted CRISPR-Cas9 system. These embryos had severely disrupted vessel formation compared to control siblings. We further show that basp1 promotes angiogenesis by upregulating β-catenin gene and the Dll4/Notch1 signaling pathway. These results, to the best of our knowledge, provide the first in vivo evidence to indicate the role of Basp1 as an angiogenesis-regulating gene and opens the potential therapeutic avenues for a wide variety of systemic angiogenesis-dependent diseases.

Genetic Background but Not Intestinal Microbiota After Co-Housing Determines Hyperoxaluria-Related Nephrocalcinosis in Common Inbred Mouse Strains.

Calcium oxalate (CaOx) crystal formation, aggregation and growth is a common cause of kidney stone disease and nephrocalcinosis-related chronic kidney disease (CKD). Genetically modified mouse strains are frequently used as an experimental tool in this context but observed phenotypes may also relate to the genetic background or intestinal microbiota. We hypothesized that the genetic background or intestinal microbiota of mice determine CaOx crystal deposition and thus the outcome of nephrocalcinosis. Indeed, Casp1 -/-, Cybb -/- or Casp1 -/-/Cybb -/- knockout mice on a 129/C57BL/6J (B6J) background that were fed an oxalate-rich diet for 14 days did neither encounter intrarenal CaOx crystal deposits nor nephrocalcinosis-related CKD. To test our assumption, we fed C57BL/6N (B6N), 129, B6J and Balb/c mice an oxalate-rich diet for 14 days. Only B6N mice displayed CaOx crystal deposits and developed CKD associated with tubular injury, inflammation and interstitial fibrosis. Intrarenal mRNA expression profiling of 64 known nephrocalcinosis-related genes revealed that healthy B6N mice had lower mRNA levels of uromodulin (Umod) compared to the other three strains. Feeding an oxalate-rich diet caused an increase in uromodulin protein expression and CaOx crystal deposition in the kidney as well as in urinary uromodulin excretion in B6N mice but not 129, B6J and Balb/c mice. However, backcrossing 129 mice on a B6N background resulted in a gradual increase in CaOx crystal deposits from F2 to F7, of which all B6N/129 mice from the 7th generation developed CaOx-related nephropathy similar to B6N mice. Co-housing experiments tested for a putative role of the intestinal microbiota but B6N co-housed with 129 mice or B6N/129 (3rd and 6th generation) mice did not affect nephrocalcinosis. In summary, genetic background but not the intestinal microbiome account for strain-specific crystal formation and, the levels of uromodulin secretion may contribute to this phenomenon. Our results imply that only littermate controls of the identical genetic background strain are appropriate when performing knockout mouse studies in this context, while co-housing is optional.

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

Simple SummarySince human studies on tumor susceptibility alleles require vast numbers of DNA samples from both cancer patients and well-matched controls, their investigation and identification in humans have been complemented using mouse models. However, a number of confounding factors are associated with this type of research, including heterogeneity, weak genetic interactions, and lifestyle habits. Inbred strains relatively recently established from wild mice are often more resistant to carcinogenic stimulation and various pathogens than standard inbred mouse strains. A Japanese wild-derived inbred mouse strain, MSM/Ms has been used to map tumor resistance loci as well as other Quantitative Trait Loci (QTL) in Japan. Furthermore, genetic tools have been developed with MSM/Ms. MSM/Ms genomic sequences are currently available, which have greatly promoted the identification of tumor resistance loci as well as genes controlling quantitative variations and provide a more detailed understanding of gene function. 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.

Biological sex, not reproductive cycle, influences peripheral blood immune cell prevalence in mice.

Traditionally the female sex, compared with the male sex, has been perceived as having greater variability in many physiological traits, including within the immune system. We investigated effects of biological sex and the female reproductive cycle on numbers of circulating leukocytes in C57BL/6J mice. We show that biological sex, but not female reproductive cyclicity, has a significant effect on peripheral blood immune cell prevalence and variability, and that sex differences were not consistent amongst common inbred laboratory mouse strains. We found that male C57BL/6J mice, compared with female mice, have greater variability in peripheral blood immunophenotype, and that this was influenced by body weight. We created summary tables for researchers to facilitate experiment planning and sample size calculations for peripheral immune cells that consider the effects of biological sex. Immunophenotyping (i.e. quantifying the number and types of circulating leukocytes) is used to characterize immune changes during health and disease, and in response to pharmacological and other interventions. Despite the importance of biological sex in immune function, there is considerable uncertainty amongst researchers as to the extent to which biological sex or the female reproductive cycle influence blood immunophenotype. We quantified circulating leukocytes by multicolour flow cytometry in young C57BL/6J mice and assessed the effects of the reproductive cycle, biological sex, and other experimental and biological factors on data variability. We found that there are no significant effects of the female reproductive cycle on the prevalence of peripheral blood B cells, NK cells, CD4+ T cells, CD8+ T cells, monocytes, or neutrophils. Immunophenotype composition and variability do not significantly change between stages of the female reproductive cycle. There are, however, sex-specific differences in immune cell prevalence, with fewer monocytes, neutrophils, and NK cells in female mice. Surprisingly, immunophenotype is more variable in male mice, and weight is a significant contributing factor. We provide tools for researchers to perform a priori sample size calculations for two-group and factorial analyses. We show that immunophenotype varies between inbred mouse strains, and that using equal sample sizes of male and female mice is not always appropriate for within-sex evaluations of immune cell populations in peripheral blood.

Angiogenic responses in a 3D micro-engineered environment of primary endothelial cells and pericytes.

Angiogenesis plays a key role in the pathology of diseases such as cancer, diabetic retinopathy, and age-related macular degeneration. Understanding the driving forces of endothelial cell migration and organization, as well as the time frame of these processes, can elucidate mechanisms of action of important pathological pathways. Herein, we have developed an organ-specific microfluidic platform recapitulating the in vivo angiogenic microenvironment by co-culturing mouse primary brain endothelial cells with brain pericytes in a three-dimensional (3D) collagen scaffold. As a proof of concept, we show that this model can be used for studying the angiogenic process and further comparing the angiogenic properties between two different common inbred mouse strains, C57BL/6J and 129S1/SvlmJ. We further show that the newly discovered angiogenesis-regulating gene Padi2 promotes angiogenesis through Dll4/Notch1 signaling by an on-chip mechanistic study. Analysis of the interplay between primary endothelial cells and pericytes in a 3D microfluidic environment assists in the elucidation of the angiogenic response.

Adaptation of retinal ganglion cell function during flickering light in the mouse

Rapid dilation of retinal vessels in response to flickering light (functional hyperemia) is a well-known autoregulatory response driven by increased neural activity in the inner retina. Little is known about flicker-induced changes of activity of retinal neurons themselves. We non-invasively investigated flicker-induced changes of retinal ganglion cell (RGC) function in common inbred mouse strains using the pattern electroretinogram (PERG), a sensitive measure of RGC function. Flicker was superimposed on the pattern stimulus at frequencies that did not generate measurable flicker-ERG and alter the PERG response. Transition from flicker at 101 Hz (control) to flicker at 11 Hz (test) at constant mean luminance induced a slow reduction of PERG amplitude to a minimum (39% loss in C57BL/6J mice and 52% loss in DBA/2J mice) 4–5 minutes after 11 Hz flicker onset, followed by a slow recovery to baseline over 20 minutes. Results demonstrate that the magnitude and temporal dynamics of RGC response induced by flicker at 11 Hz can be non-invasively assessed with PERG in the mouse. This allows investigating the functional phenotype of different mouse strains as well as pathological changes in glaucoma and optic nerve disease. The non-contact flicker-PERG method opens the possibility of combined assessment of neural and vascular response dynamics.

The Evolution of Polymorphic Hybrid Incompatibilities in House Mice.

Resolving the mechanistic and genetic bases of reproductive barriers between species is essential to understanding the evolutionary forces that shape speciation. Intrinsic hybrid incompatibilities are often treated as fixed between species, yet there can be considerable variation in the strength of reproductive isolation between populations. The extent and causes of this variation remain poorly understood in most systems. We investigated the genetic basis of variable hybrid male sterility (HMS) between two recently diverged subspecies of house mice, Mus musculus domesticus and Mus musculus musculus We found that polymorphic HMS has a surprisingly complex genetic basis, with contributions from at least five autosomal loci segregating between two closely related wild-derived strains of M. m. musculus One of the HMS-linked regions on chromosome 4 also showed extensive introgression among inbred laboratory strains and transmission ratio distortion (TRD) in hybrid crosses. Using additional crosses and whole genome sequencing of sperm pools, we showed that TRD was limited to hybrid crosses and was not due to differences in sperm motility between M. m. musculus strains. Based on these results, we argue that TRD likely reflects additional incompatibilities that reduce hybrid embryonic viability. In some common inbred strains of mice, selection against deleterious interactions appears to have unexpectedly driven introgression at loci involved in epistatic hybrid incompatibilities. The highly variable genetic basis to F1 hybrid incompatibilities between closely related mouse lineages argues that a thorough dissection of reproductive isolation will require much more extensive sampling of natural variation than has been commonly utilized in mice and other model systems.

A novel genetic model to explore the Brenner hypothesis: Linking nephron endowment and number with hypertension

Nephron endowment, the total number of nephrons an individual is born with, is determined by both genetic and environmental factors during embryonic development. In 1988, Brenner hypothesized that there was an inverse relationship between nephron number and hypertension. Over the course of one’s lifetime it is predicted that even healthy individuals will lose a significant percentage of nephrons as part of normal aging. Thus, a low nephron endowment at birth or in combination with age- or disease-related nephron loss could pre-dispose individuals to the development of hypertension. Currently, it is not clear what minimal number (ie, threshold) of nephrons is associated with susceptibility to glomeruli injury or hypertension, due in part to the lack of relevant animal models. The BPH2 mouse is a unique genetic model of hypertension that has a normotensive line (BPN3 mice) as well as a hypotensive line (BPL1 mice) derived from the original breeding of eight common inbred strains of mice. Thus, we hypothesize that the differences in blood pressure observed in BPH2, BPN3, and BPL1 mice will correlate inversely with nephron number as predicted by the Brenner hypothesis. If our hypothesis is true, then the BPH2 mouse model will provide a unique experimental model to study the impact of nephron endowment and nephron number on susceptibility to renal injury and hypertension.

Identification of Padi2 as a novel angiogenesis-regulating gene by genome association studies in mice.

Recent findings indicate that growth factor-driven angiogenesis is markedly influenced by genetic variation. This variation in angiogenic responsiveness may alter the susceptibility to a number of angiogenesis-dependent diseases. Here, we utilized the genetic diversity available in common inbred mouse strains to identify the loci and candidate genes responsible for differences in angiogenic response. The corneal micropocket neovascularization assay was performed on 42 different inbred mouse strains using basic fibroblast growth factor (bFGF) pellets. We performed a genome-wide association study utilizing efficient mixed-model association (EMMA) mapping using the induced vessel area from all strains. Our analysis yielded five loci with genome-wide significance on chromosomes 4, 8, 11, 15 and 16. We further refined the mapping on chromosome 4 within a haplotype block containing multiple candidate genes. These genes were evaluated by expression analysis in corneas of various inbred strains and in vitro functional assays in human microvascular endothelial cells (HMVECs). Of these, we found the expression of peptidyl arginine deiminase type II (Padi2), known to be involved in metabolic pathways, to have a strong correlation with a haplotype shared by multiple high angiogenic strains. In addition, inhibition of Padi2 demonstrated a dosage-dependent effect in HMVECs. To investigate its role in vivo, we knocked down Padi2 in transgenic kdrl:zsGreen zebrafish embryos using morpholinos. These embryos had disrupted vessel formation compared to control siblings. The impaired vascular pattern was partially rescued by human PADI2 mRNA, providing evidence for the specificity of the morphant phenotype. Taken together, our study is the first to indicate the potential role of Padi2 as an angiogenesis-regulating gene. The characterization of Padi2 and other genes in associated pathways may provide new understanding of angiogenesis regulation and novel targets for diagnosis and treatment of a wide variety of angiogenesis-dependent diseases.

Anatomical Variation of the Tarsus in Common Inbred Mouse Strains.

Rodent models are used for a variety of orthopedic research applications; however, anatomy references include mostly artistic representations. Advanced imaging techniques, including micro-computed tomography (microCT), can provide more accurate representations of subtle anatomical characteristics. A recent microCT atlas of laboratory mouse (Mus musculus) anatomy depicts the central and tarsal bone III (T3) as a single bone, differing from previous references. Fusion of tarsal bones is generally characterized as pathological secondary to mutations associated with growth factors, and normal variation has not been documented in the mouse tarsus. Therefore, it is unclear if this fusion is a normal or a pathological characteristic. The aim of this study is to characterize the tarsus of the laboratory mouse and compare it to the rat and selected outgroup species (i.e., white-footed mouse) via microCT and histology to determine if the central and T3 are separate or fused into a single bone. Laboratory mice (C57/Bl6 [n = 17] and BalbC [n = 2]) and rats (n = 5) were scanned with microCT. A representative laboratory mouse from each strain was evaluated histologically via serial sagittal sections through the mid-tarsus. General pedal anatomy was similar between all species; however, the central and T3 bones were fused in all laboratory mice but not the rat or white-footed mouse. A band of hyaline cartilage was identified within the fused bone of the laboratory mice. We conclude that the fusion found is a normal characteristic in laboratory mice, but timing of the fusion remains ambiguous. Anat Rec, 300:450-459, 2017. © 2016 Wiley Periodicals, Inc.

Abstract 052: Direct Correlation Between Blood Pressure and Nephron Endowment in a Genetic Mouse Model of Hypertension

Blood pressure high (BPH2) mice represent a novel genetic mouse model of hypertension that was derived from an 8-way cross of common inbred strains of mice. Mice derived from the original cross were segregated by blood pressure and then inbred to establish distinct mouse lines including the BPH2 line, a normotensive genetic control (blood pressure normal; BPN3) as well as a blood pressure low (BPL1) line. The goal of the present study was to test the hypothesis that the level of blood pressure in BPH2, BPN3, BPL1, and C57Bl/6 (normotensive inbred control) mice correlates with nephron endowment. Systolic blood pressure (SBP) was measured in male BPH2, BPN3, BPL1, and C57BL/6 mice (n=6/group) using tail-cuff plethysmography. SBP in BPH2, BPN3, BPL1, and C57BL/6 mice averaged 152±2, 117±1; 105±4; and 107±3 mm Hg, respectively. SBP was significantly greater (P<0.05) in BPH2 mice compared to the other three groups of mice. In contrast, SBP was found to be similar (P>0.05) between BPL1 and C57BL/6 mice and significantly (P<0.05) lower than that in either BPH2 or BPN3 mice. Total kidney weight/body weight ratios were found to be similar (P>0.05) in BPH2 and BPN3 mice and significantly (P<0.05) higher than that in BPL1 and C57BL/6 mice. Nephron number as assessed by the acid maceration technique revealed that total nephron number in BPH2, BPN3, BPL1, and C57Bl/6 averaged 10,409±285, 25,333±478, 27,300±445 and 22,533±668 nephrons per kidney, respectively. There was an extremely significant correlation (R2=0.779; P<0.0001) between nephron number and systolic blood pressure. These data provide evidence that blood pressure in a genetic mouse model of hypertension correlates with total nephron number. These findings are consistent with the emerging concept that nephron endowment at birth or progressive loss of nephrons with age or disease directly impacts blood pressure. Thus, we suggest that the BPH2 mouse can serve as an important experimental model to investigate the intrinsic relationship between nephron endowment and blood pressure.

Temporal dynamics of the developing lung transcriptome in three common inbred strains of laboratory mice reveals multiple stages of postnatal alveolar development.

To characterize temporal patterns of transcriptional activity during normal lung development, we generated genome wide gene expression data for 26 pre- and post-natal time points in three common inbred strains of laboratory mice (C57BL/6J, A/J, and C3H/HeJ). Using Principal Component Analysis and least squares regression modeling, we identified both strain-independent and strain-dependent patterns of gene expression. The 4,683 genes contributing to the strain-independent expression patterns were used to define a murine Developing Lung Characteristic Subtranscriptome (mDLCS). Regression modeling of the Principal Components supported the four canonical stages of mammalian embryonic lung development (embryonic, pseudoglandular, canalicular, saccular) defined previously by morphology and histology. For postnatal alveolar development, the regression model was consistent with four stages of alveolarization characterized by episodic transcriptional activity of genes related to pulmonary vascularization. Genes expressed in a strain-dependent manner were enriched for annotations related to neurogenesis, extracellular matrix organization, and Wnt signaling. Finally, a comparison of mouse and human transcriptomics from pre-natal stages of lung development revealed conservation of pathways associated with cell cycle, axon guidance, immune function, and metabolism as well as organism-specific expression of genes associated with extracellular matrix organization and protein modification. The mouse lung development transcriptome data generated for this study serves as a unique reference set to identify genes and pathways essential for normal mammalian lung development and for investigations into the developmental origins of respiratory disease and cancer. The gene expression data are available from the Gene Expression Omnibus (GEO) archive (GSE74243). Temporal expression patterns of mouse genes can be investigated using a study specific web resource (http://lungdevelopment.jax.org).

Sequence Diversity, Intersubgroup Relationships, and Origins of the Mouse Leukemia Gammaretroviruses of Laboratory and Wild Mice

Mouse leukemia viruses (MLVs) are found in the common inbred strains of laboratory mice and in the house mouse subspecies ofMus musculus Receptor usage and envelope (env) sequence variation define three MLV host range subgroups in laboratory mice: ecotropic, polytropic, and xenotropic MLVs (E-, P-, and X-MLVs, respectively). These exogenous MLVs derive from endogenous retroviruses (ERVs) that were acquired by the wild mouse progenitors of laboratory mice about 1 million years ago. We analyzed the genomes of seven MLVs isolated from Eurasian and American wild mice and three previously sequenced MLVs to describe their relationships and identify their possible ERV progenitors. The phylogenetic tree based on the receptor-determining regions ofenvproduced expected host range clusters, but these clusters are not maintained in trees generated from other virus regions. Colinear alignments of the viral genomes identified segmental homologies to ERVs of different host range subgroups. Six MLVs show close relationships to a small xenotropic ERV subgroup largely confined to the inbred mouse Y chromosome.envvariations define three E-MLV subtypes, one of which carries duplications of various sizes, sequences, and locations in the proline-rich region ofenv Outside theenvregion, all E-MLVs are related to different nonecotropic MLVs. These results document the diversity in gammaretroviruses isolated from globally distributedMussubspecies, provide insight into their origins and relationships, and indicate that recombination has had an important role in the evolution of these mutagenic and pathogenic agents. Laboratory mice carry mouse leukemia viruses (MLVs) of three host range groups which were acquired from their wild mouse progenitors. We sequenced the complete genomes of seven infectious MLVs isolated from geographically separated Eurasian and American wild mice and compared them with endogenous germ line retroviruses (ERVs) acquired early in house mouse evolution. We did this because the laboratory mouse viruses derive directly from specific ERVs or arise by recombination between different ERVs. The six distinctively different wild mouse viruses appear to be recombinants, often involving different host range subgroups, and most are related to a distinctive, largely Y-chromosome-linked MLV ERV subtype. MLVs with ecotropic host ranges show the greatest variability with extensive inter- and intrasubtype envelope differences and with homologies to other host range subgroups outside the envelope. The sequence diversity among these wild mouse isolates helps define their relationships and origins and emphasizes the importance of recombination in their evolution.

Integration of genome-wide association and extant brain expression QTL identifies candidate genes influencing prepulse inhibition in inbred F1 mice.

Genetic association mapping in structured populations of model organisms can offer a fruitful complement to human genetic studies by generating new biological hypotheses about complex traits. Here we investigated prepulse inhibition (PPI), a measure of sensorimotor gating that is disrupted in a number of psychiatric disorders. To identify genes that influence PPI, we constructed a panel of half-sibs by crossing 30 females from common inbred mouse strains with inbred C57BL/6J males to create male and female F1 offspring. We used publicly available single nucleotide polymorphism (SNP) genotype data from these inbred strains to perform a genome-wide association scan using a dense panel of over 150,000 SNPs in a combined sample of 604 mice representing 30 distinct F1 genotypes. We identified two independent PPI-associated loci on Chromosomes 2 and 7, each of which explained 12-14% of the variance in PPI. Searches of available databases did not identify any plausible causative coding polymorphisms within these loci. However, previously collected expression quantitative trait locus (eQTL) data from hippocampus and striatum indicated that the SNPs on Chromosomes 2 and 7 that showed the strongest association with PPI were also strongly associated with expression of several transcripts, some of which have been implicated in human psychiatric disorders. This integrative approach successfully identified a focused set of genes which can be prioritized for follow-up studies. More broadly, our results show that F1 crosses among common inbred strains can be used in combination with other informatics and expression datasets to identify candidate genes for complex behavioral traits.

Within-strain variation in behavior differs consistently between common inbred strains of mice.

Genetic and environmental factors interact throughout life and give rise to individual differences, i.e., individuality. The diversifying effect of environmental factors is counteracted by genetic mechanisms to yield persistence of specific features (robustness). Here, we compared robustness between cohorts of isogenic mice of eight different commonly used strains by analyzing to what extent environmental variation contributed to individuality in each of the eight genotypes, using a previously published dataset. Behavior was assessed in the home-cage, providing control over environmental factors, to reveal within-strain variability in numerous spontaneous behaviors. Indeed, despite standardization and in line with previous studies, substantial variability among mice of the same inbred strain was observed. Strikingly, across a multidimensional set of 115 behavioral parameters, several strains consistently ranked high in within-strain variability (DBA/2J, 129S1/Sv A/J and NOD/LtJ), whereas other strains ranked low (C57BL/6J and BALB/c). Strain rankings of within-strain variability in behavior were confirmed in an independent, previously published behavioral dataset using conventional behavioral tests administered to different mice from the same breeding colonies. Together, these show that genetically inbred mouse strains consistently differ in phenotypic robustness against environmental variation, suggesting that genetic factors contribute to variation in robustness.