Genotype-specific environmental impact on the variance of blood values in inbred and F1 hybrid mice

Demonstration of Safety in Wild Type Mice of npFOXF1, a Novel Nanoparticle-Based Gene Therapy for Alveolar Capillary Dysplasia with Misaligned Pulmonary Veins

Introduction

Alveolar Capillary Dysplasia with Misaligned Pulmonary Veins (ACDMPV) is a fatal congenital disease resulting from a pulmonary vascular endothelial deficiency of FOXF1, producing abnormal morphogenesis of alveolar capillaries, malpositioned pulmonary veins and disordered development of lung lobes. Affected neonates suffer from cyanosis, severe breathing insufficiency, pulmonary hypertension, and death typically within days to weeks after birth. Currently, no treatment exists for ACDMPV, although recent murine research in the Kalinichenko lab demonstrates nanoparticle delivery improves survival and reconstitutes normal alveolar-capillary architecture. The aim of the present study is to investigate the safety of intravenous administration of FOXF1-expressing PEI-PEG nanoparticles (npFOXF1), our pioneering treatment for ACDMPV.

Methods

npFOXF1 was constructed, validated, and subsequently administered in a single dose to postnatal day 14 (P14) mice via retro-orbital injection. Biochemical, serologic, and histologic safety were monitored at postnatal day 16 (P16) and postnatal day 21 (P21).

Results

With treatment we observed no lethality, and the general condition of mice revealed no obvious abnormalities. Serum chemistry, whole blood, and histologic toxicity was assayed on P16 and P21 and revealed no abnormality.

Discussion

In conclusion, npFOXF1 has a very good safety profile and combined with preceding studies showing therapeutic efficacy, npFOXF1 can be considered as a good candidate therapy for ACDMPV in human neonates.

Effects of Daytime Blue-Enriched LED Light on Physiologic Parameters of Three Common Mouse Strains Maintained on an IVC System

Light has been a crucial part of everyday life since the beginning of time. Most recently, light-emitting diode (LED) light enriched in the blue-appearing portion of the visible spectrum (465 to 485 nm), which is more efficient in energy use, is becoming the normal lighting technology in facilities around the world. Previous reports revealed that blue-enriched LED light at day (bLAD) enhances animal health and wellbeing as compared with cool white fluorescent (CWF) lighting. We hypothesized that bLAD, compared with CWF light, has a positive influence on basic physiologic indices such as food consumption, water consumption, weight gain, nesting behavior, complete blood count, and blood chemistry profile. To test this, we allocated 360 mice into equal-sized groups by sex, strain (C3H/HeNCrl, C57BL/6NCrl, BALB/cAnNCrl), lighting conditions, and 6 blood collection time points (n = 5 mice/sex/strain/lighting condition/time point). Food consumption, water consumption, body weight, nest location, and nest type were recorded every 3 d. At the end of the study, all mice were anesthetized over a period of 1 wk and blood was collected via cardiocentesis at 6 different time points. Overall, male C3H/HeNCrl consumed more food under bLAD conditions as compared with CWF conditions; male C3H/HeNCrl had lower cholesterol levels under bLAD conditions than under CWF conditions; female BALB/cAnNCrl mice had higher serum total protein under bLAD conditions than under CWF conditions; female C57BL/6NCrl mice had higher phosphorus levels under bLAD conditions than under CWF conditions, and female C3H/HeNCrl mice had a higher neutrophil count under bLAD conditions as compared with CWF conditions. Although sex and strain differences were found in various physiologic parameters under bLAD as compared with CWF lighting conditions, the differences were minimal. Thus, this study suggests that for these strains of mice, bLAD and CWF are largely equivalent with regard to indices of health and wellbeing, although some differences could affect research outcomes.

Analysis of the sex-specific variability of blood parameters in C3H inbred mice by using data from a long-term, high-throughput project

Mice are important models for biomedical research by providing the possibility of standardizing genetic background and environmental conditions, which both affect phenotypic variability. Use of both sexes in experiments is strongly recommended because of possible differences in the outcome. However, sex-specific phenotypic variability is discussed with regard to putative consequences on the group size which is necessary for achieving valid and reproducible results. Here, we retrospectively analyzed the sex-specific variability of 25 blood parameters of C3H inbred mice in two different mouse facilities withinthe long-term, high-throughput Munich ENU mouse mutagenesis project. Using the 95 % data range, data of4,780-20,706 mice per parameter were analyzed and resulted in ratios of the coefficient of variation (= female CV / (female CV + male CV)) from 0.44 to 0.58 for the 25 parameters, with an overall mean of 0.51 in both facilities. Together with data analyses of three additional, smaller studies with 72-247 animals per parameter examined and various genetic backgrounds (inbred strains, F1 hybrids) included, hints for reproducible sex-specific variability were observed for particular parameters. Thus, the overall analysis comprising all 25 clinical chemical and hematological parameters of the standardized, long-term analysis of a high number of group housed, young adult, twelve-week-old C3H inbred mice showed no evidence for substantial sex-specific variability. The results may provide a basis for the examination of sex-specific variability in particular blood parameters.

Laboratory diagnostics of murine blood for detection of mouse cytomegalovirus (MCMV)-induced hepatitis

Mouse models are important and versatile tools to study mechanisms and novel therapies of human disease in vivo. Both, the number and the complexity of murine models are constantly increasing and modification of genes of interest as well as any exogenous challenge may lead to unanticipated biological effects. Laboratory diagnostics of blood samples provide a comprehensive and rapid screening for multiple organ function and are fundamental to detect human disease. Here, we adapt an array of laboratory medicine-based tests commonly used in humans to establish a platform for standardized, multi-parametric, and quality-controlled diagnostics of murine blood samples. We determined sex-dependent reference intervals of 51 commonly used laboratory medicine tests for samples obtained from the C57BL/6J mouse strain. As a proof of principle, we applied these diagnostic tests in a mouse cytomegalovirus (MCMV) infection model to screen for organ damage. Consistent with histopathological findings, plasma concentrations of liver-specific enzymes were elevated, supporting the diagnosis of a virus-induced hepatitis. Plasma activities of aminotransferases correlated with viral loads in livers at various days after MCMV infection and discriminated infected from non-infected animals. This study provides murine blood reference intervals of common laboratory medicine parameters and illustrates the use of these tests for diagnosis of infectious disease in experimental animals.

Searching for novel biomarkers using a mouse model of CLN3-Batten disease

CLN3-Batten disease is a rare, autosomal recessive disorder involving seizures, visual, motor and cognitive decline, and premature death. The Cln3Δex7/8 mouse model recapitulates several phenotypic characteristics of the most common 1.02kb disease-associated deletion. Identification of reproducible biomarker(s) to facilitate longitudinal monitoring of disease progression and provide readouts for therapeutic response has remained elusive. One factor that has complicated the identification of suitable biomarkers in this mouse model has been that variations in animal husbandry appear to significantly influence readouts. In the current study, we cross-compared a number of biological parameters in blood from Cln3Δex7/8 mice and control, non-disease mice on the same genetic background from multiple animal facilities in an attempt to better define a surrogate marker of CLN3-Batten disease. Interestingly, we found that significant differences between Batten and non-disease mice found at one site were generally not maintained across different facilities. Our results suggest that colony variation in the Cln3Δex7/8 mouse model of CLN3-Batten disease can influence potential biomarkers of the disease.

Development of Th17-Associated Interstitial Kidney Inflammation in Lupus-Prone Mice Lacking the Gene Encoding STAT-1

OBJECTIVE

Type I interferon (IFN) signaling is a central pathogenic pathway in systemic lupus erythematosus (SLE), and therapeutics targeting type I IFN signaling are in development. Multiple proteins with overlapping functions play a role in IFN signaling, but the signaling events downstream of receptor engagement are unclear. This study was undertaken to investigate the roles of the type I and type II IFN signaling components IFN-α/β/ω receptor 2 (IFNAR-2), IFN regulatory factor 9 (IRF-9), and STAT-1 in a mouse model of SLE.

METHODS

We used immunohistochemical staining and highly multiplexed assays to characterize pathologic changes in histology, autoantibody production, cytokine/chemokine profiles, and STAT phosphorylation in order to investigate the individual roles of IFNAR-2, IRF-9, and STAT-1 in MRL/lpr mice.

RESULTS

We found that STAT-1(-/-) mice, but not IRF-9(-/-) or IFNAR-2(-/-) mice, developed interstitial nephritis characterized by infiltration with retinoic acid receptor-related orphan nuclear receptor γt-positive lymphocytes, macrophages, and eosinophils. Despite pronounced interstitial kidney disease and abnormal kidney function, STAT-1(-/-) mice had decreased proteinuria, glomerulonephritis, and autoantibody production. Phosphospecific flow cytometry revealed shunting of STAT phosphorylation from STAT-1 to STAT-3/4.

CONCLUSION

We describe unique contributions of STAT-1 to pathology in different kidney compartments in a mouse model, and provide potentially novel insight into tubulointerstitial nephritis, a poorly understood complication that predicts end-stage kidney disease in SLE patients.

Exome sequencing identifies a nonsense mutation in Fam46a associated with bone abnormalities in a new mouse model for skeletal dysplasia

We performed exome sequencing for mutation discovery of an ENU (N-ethyl-N-nitrosourea)-derived mouse model characterized by significant elevated plasma alkaline phosphatase (ALP) activities in female and male mutant mice, originally named BAP014 (bone screen alkaline phosphatase #14). We identified a novel loss-of-function mutation within the Fam46a (family with sequence similarity 46, member A) gene (NM_001160378.1:c.469G>T, NP_001153850.1:p.Glu157*). Heterozygous mice of this mouse line (renamed Fam46a (E157*Mhda)) had significantly high ALP activities and apparently no other differences in morphology compared to wild-type mice. In contrast, homozygous Fam46a (E157*Mhda) mice showed severe morphological and skeletal abnormalities including short stature along with limb, rib, pelvis, and skull deformities with minimal trabecular bone and reduced cortical bone thickness in long bones. ALP activities of homozygous mutants were almost two-fold higher than in heterozygous mice. Fam46a is weakly expressed in most adult and embryonic tissues with a strong expression in mineralized tissues as calvaria and femur. The FAM46A protein is computationally predicted as a new member of the superfamily of nucleotidyltransferase fold proteins, but little is known about its function. Fam46a (E157*Mhda) mice are the first mouse model for a mutation within the Fam46a gene.

You are what you eat, or are you? The challenges of translating high-fat-fed rodents to human obesity and diabetes

Obesity and type 2 diabetes mellitus (T2DM) are rapidly growing worldwide epidemics with major health consequences. Various human-based studies have confirmed that both genetic and environmental factors (particularly high-caloric diets and sedentary lifestyle) greatly contribute to human T2DM. Interactions between obesity, insulin resistance and β-cell dysfunction result in human T2DM, but the mechanisms regulating the interplay among these impairments remain unclear. Rodent models of high-fat diet (HFD)-induced obesity have been used widely to study human obesity and T2DM. With >9000 publications on PubMed over the past decade alone, many aspects of rodent T2DM have been elucidated; however, correlation to human obesity/diabetes remains poor. This review investigates the reasons for this translational discrepancy by critically evaluating rodent HFD models. Dietary modification in rodents appears to have limited translatable benefit for understanding and treating human obesity and diabetes due—at least in part—to divergent dietary compositions, species/strain and gender variability, inconsistent disease penetrance, severity and duration and lack of resemblance to human obesogenic pathophysiology. Therefore future research efforts dedicated to acquiring translationally relevant data—specifically human data, rather than findings based on rodent studies—would accelerate our understanding of disease mechanisms and development of therapeutics for human obesity/T2DM.

An ENU mutagenesis-derived mouse model with a dominant Jak1 mutation resembling phenotypes of systemic autoimmune disease

Within the Munich, Germany, N-ethyl-N-nitrosourea mouse mutagenesis program, we isolated a dominant Jak1 mouse model resembling phenotypic characteristics related to autoimmune disease. Chromosomal sequencing revealed a new Jak1 (p.Ser645Pro) point mutation at the conserved serine of the pseudokinase domain, corresponding to a somatic human mutation (p.Ser646Phe) inducing a constitutive activation of the Janus kinase (JAK)/STAT pathway. Morphologically, all Jak1(S645P+/-) mice showed a progressive structural deterioration of ears starting at the age of 4 months, with mononuclear cell infiltration into the dermis. Female mutant mice, in particular, developed severe skin lesions in the neck from 7 months of age. The IHC analysis of these lesions showed an activation of Stat3 downstream to Jak1(S645P) and elevated tissue levels of IL-6. Histopathological analysis of liver revealed a nodular regenerative hyperplasia. In the spleen, the number of Russell bodies was doubled, correlating with significant increased levels of all immunoglobulin isotypes and anti-DNA antibodies in serum. Older mutant mice developed thrombocytopenia and altered microcytic red blood cell counts. Jak1(S645P+/-) mice showed phenotypes related to impaired bone metabolism as increased carboxy-terminal collagen cross-link-1 levels and alkaline phosphatase activities in plasma, hypophosphatemia, and strongly decreased bone morphometric values. Taken together, Jak1(S645P+/-) mice showed an increased activation of the IL-6-JAK-STAT pathway leading to a systemic lupus erythematosus-like phenotype and offering a new valuable tool to study the role of the JAK/STAT pathway in disease development.

The physiological effects of deleting the mouse SLC30A8 gene encoding zinc transporter-8 are influenced by gender and genetic background

Objective

The SLC30A8 gene encodes the islet-specific transporter ZnT-8, which is hypothesized to provide zinc for insulin-crystal formation. A polymorphic variant in SLC30A8 is associated with altered susceptibility to type 2 diabetes. Several groups have examined the effect of global Slc30a8 gene deletion but the results have been highly variable, perhaps due to the mixed 129SvEv/C57BL/6J genetic background of the mice studied. We therefore sought to remove the conflicting effect of 129SvEv-specific modifier genes.

Methods

The impact of Slc30a8 deletion was examined in the context of the pure C57BL/6J genetic background.

Results

Male C57BL/6J Slc30a8 knockout (KO) mice had normal fasting insulin levels and no change in glucose-stimulated insulin secretion (GSIS) from isolated islets in marked contrast to the ∼50% and ∼35% decrease, respectively, in both parameters observed in male mixed genetic background Slc30a8 KO mice. This observation suggests that 129SvEv-specific modifier genes modulate the impact of Slc30a8 deletion. In contrast, female C57BL/6J Slc30a8 KO mice had reduced (∼20%) fasting insulin levels, though this was not associated with a change in fasting blood glucose (FBG), or GSIS from isolated islets. This observation indicates that gender also modulates the impact of Slc30a8 deletion, though the physiological explanation as to why impaired insulin secretion is not accompanied by elevated FBG is unclear. Neither male nor female C57BL/6J Slc30a8 KO mice showed impaired glucose tolerance.

Conclusions

Our data suggest that, despite a marked reduction in islet zinc content, the absence of ZnT-8 does not have a substantial impact on mouse physiology.

New mouse models for metabolic bone diseases generated by genome-wide ENU mutagenesis

Metabolic bone disorders arise as primary diseases or may be secondary due to a multitude of organ malfunctions. Animal models are required to understand the molecular mechanisms responsible for the imbalances of bone metabolism in disturbed bone mineralization diseases. Here we present the isolation of mutant mouse models for metabolic bone diseases by phenotyping blood parameters that target bone turnover within the large-scale genome-wide Munich ENU Mutagenesis Project. A screening panel of three clinical parameters, also commonly used as biochemical markers in patients with metabolic bone diseases, was chosen. Total alkaline phosphatase activity and total calcium and inorganic phosphate levels in plasma samples of F1 offspring produced from ENU-mutagenized C3HeB/FeJ male mice were measured. Screening of 9,540 mice led to the identification of 257 phenodeviants of which 190 were tested by genetic confirmation crosses. Seventy-one new dominant mutant lines showing alterations of at least one of the biochemical parameters of interest were confirmed. Fifteen mutations among three genes (Phex, Casr, and Alpl) have been identified by positional-candidate gene approaches and one mutation of the Asgr1 gene, which was identified by next-generation sequencing. All new mutant mouse lines are offered as a resource for the scientific community.

Generation of N-ethyl-N-nitrosourea-induced mouse mutants with deviations in hematological parameters

Research on hematological disorders relies on suitable animal models. We retrospectively evaluated the use of the hematological parameters hematocrit (HCT), hemoglobin (HGB), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), mean corpuscular volume (MCV), red blood cell count (RBC), white blood cell count (WBC), and platelet count (PLT) in the phenotype-driven Munich N-ethyl-N-nitrosourea (ENU) mouse mutagenesis project as parameters for the generation of novel animal models for human diseases. The analysis was carried out on more than 16,000 G1 and G3 offspring of chemically mutagenized inbred C3H mice to detect dominant and recessive mutations leading to deviations in the levels of the chosen parameters. Identification of animals exhibiting altered values and transmission of the phenotypic deviations to the subsequent generations led to the successful establishment of mutant lines for the parameters MCV, RBC, and PLT. Analysis of the causative mutation was started in selected lines, thereby revealing a novel mutation in the transferrin receptor gene (Tfrc) in one line. Thus, novel phenotype-driven mouse models were established to analyze the genetic components of hematological disorders.

Establishing normal plasma and 24-hour urinary biochemistry ranges in C3H, BALB/c and C57BL/6J mice following acclimatization in metabolic cages

Physiological studies of mice are facilitated by normal plasma and 24-hour urinary reference ranges, but variability of these parameters may increase due to stress that is induced by housing in metabolic cages. We assessed daily weight, food and water intake, urine volume and final day measurements of the following: plasma sodium, potassium, chloride, urea, creatinine, calcium, phosphate, alkaline phosphatase, albumin, cholesterol and glucose; and urinary sodium, potassium, calcium, phosphate, glucose and protein in 24- to 30-week-old C3H/HeH, BALB/cAnNCrl and C57BL/6J mice. Between 15 and 20 mice of each sex from all three strains were individually housed in metabolic cages with ad libitum feeding for up to seven days. Acclimatization was evaluated using general linear modelling for repeated measures and comparison of biochemical data was by unpaired t-test and analysis of variance (SPSS version 12.0.1). Following an initial 5-10% fall in body weight, daily dietary intake, urinary output and weight in all three strains reached stable values after 3-4 days of confinement. Significant differences in plasma glucose, cholesterol, urea, chloride, calcium and albumin, and urinary glucose, sodium, phosphate, calcium and protein were observed between strains and genders. Thus, these results provide normal reference values for plasma and urinary biochemistry in three strains housed in metabolic cages and demonstrate that 3-4 days are required to reach equilibrium in metabolic cage studies. These variations due to strain and gender have significant implications for selecting the appropriate strain upon which to breed genetically-altered models of metabolic and renal disease.

Dll1 haploinsufficiency in adult mice leads to a complex phenotype affecting metabolic and immunological processes

BACKGROUND

The Notch signaling pathway is an evolutionary conserved signal transduction pathway involved in embryonic patterning and regulation of cell fates during development and self-renewal. Recent studies have demonstrated that this pathway is integral to a complex system of interactions, involving as well other signal transduction pathways, and implicated in distinct human diseases. Delta-like 1 (Dll1) is one of the known ligands of the Notch receptors. The role of the Notch ligands is less well understood. Loss-of-function of Dll1 leads to embryonic lethality, but reduction of Delta-like 1 protein levels has not been studied in adult stage.

METHODOLOGY/PRINCIPAL FINDINGS

Here we present the haploinsufficient phenotype of Dll1 and a missense mutant Dll1 allele (Dll1(C413Y)). Haploinsufficiency leads to a complex phenotype with several biological processes altered. These alterations reveal the importance of Dll1 mainly in metabolism, energy balance and in immunology. The animals are smaller, lighter, with altered fat to lean ratio and have increased blood pressure and a slight bradycardia. The animals have reduced cholesterol and triglyceride levels in blood. At the immunological level a subtle phenotype is observed due to the effect and fine-tuning of the signaling network at the different levels of differentiation, proliferation and function of lymphocytes. Moreover, the importance of the proteolytic regulation of the Notch signaling network emphasized.

CONCLUSIONS/SIGNIFICANCE

In conclusion, slight alterations in one player of Notch signaling alter the entire organism, emphasizing the fine-tuning character of this pathway in a high number of processes.

N-ethyl-N-nitrosourea mutagenesis produced a small number of mice with altered plasma electrolyte levels

Background

Clinical chemical blood analysis including plasma electrolytes is routinely carried out for the diagnosis of various organ diseases. Phenotype-driven N-ethyl-N-nitrosourea (ENU) mouse mutagenesis projects used plasma electrolytes as parameters for the generation of novel animal models for human diseases.

Methods

Here, we retrospectively evaluated the use of the plasma electrolytes calcium, chloride, inorganic phosphorus, potassium and sodium in the Munich ENU mouse mutagenesis project where clinical chemical blood analysis was carried out on more than 20,000 G1 and G3 offspring of chemically mutagenized inbred C3H mice to detect dominant and recessive mutations leading to deviations in various plasma parameter levels.

Results

We identified a small number of animals consistently exhibiting altered plasma electrolyte values. Transmission of the phenotypic deviations to the subsequent generations led to the successful establishment of mutant lines for the parameters calcium and potassium. Published data from other phenotype-driven ENU projects also included only a small number of mutant lines which were generated according to altered plasma electrolyte levels.

Conclusion

Thus, use of plasma electrolytes detected few mouse mutants in ENU projects compared to other clinical chemical blood parameters.

Generation of N-ethyl-N-nitrosourea-induced mouse mutants with deviations in plasma enzyme activities as novel organ-specific disease models

Measurement of plasma enzyme activities is part of routine medical examination protocols and provides valuable parameters for the diagnosis of various organ diseases. In the phenotype-driven Munich N-ethyl-N-nitrosourea (ENU) mouse mutagenesis project, clinical chemical blood analysis was carried out on more than 20,000 G1 and G3 offspring of chemically mutagenized inbred C3H mice to detect dominant and recessive mutations leading to deviations in the plasma enzyme activities of alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, alpha-amylase and creatine kinase. We identified a large number of animals that consistently exhibited altered plasma enzyme activities. Transmission of the phenotypic deviations to the subsequent generations led to the successful establishment of mutant lines for each parameter. Breeding experiments in selected lines detected the linkage of the causative mutations to defined chromosomal regions. Subsequently, identification of the mutated genes was successfully carried out in chosen lines, resulting in a novel alkaline phosphatase liver/bone/kidney (Alpl) alteration in one line and the strong indication for a dystrophin (Dmd) alteration in another line. The mouse mutants with abnormal plasma enzyme activities recovered in the Munich ENU project are novel tools for the systematic dissection of the pathogenesis of organ diseases.

Systemic first-line phenotyping

With the completion of the mouse genome sequence an essential task for biomedical sciences in the twenty-first century will be the generation and functional analysis of mouse models for every gene in the mammalian genome. More than 30,000 mutations in ES cells will be engineered and thousands of mouse disease models will become available over the coming years by the collaborative effort of the International Mouse Knockout Consortium. In order to realize the full value of the mouse models proper characterization, archiving and dissemination of mouse disease models to the research community have to be performed. Phenotyping centers (mouse clinics) provide the necessary capacity, broad expertise, equipment, and infrastructure to carry out large-scale systemic first-line phenotyping. Using the example of the German Mouse Clinic (GMC) we will introduce the reader to the different aspects of the organization of a mouse clinic and present selected methods used in first-line phenotyping.

ER stress-mediated apoptosis in a new mouse model of osteogenesis imperfecta

Osteogenesis imperfecta is an inherited disorder characterized by increased bone fragility, fractures, and osteoporosis, and most cases are caused by mutations affecting the type I collagen genes. Here, we describe a new mouse model for Osteogenesis imperfecta termed Aga2 (abnormal gait 2) that was isolated from the Munich N-ethyl-N-nitrosourea mutagenesis program and exhibited phenotypic variability, including reduced bone mass, multiple fractures, and early lethality. The causal gene was mapped to Chromosome 11 by linkage analysis, and a C-terminal frameshift mutation was identified in the Col1a1 (procollagen type I, alpha 1) gene as the cause of the disorder. Aga2 heterozygous animals had markedly increased bone turnover and a disrupted native collagen network. Further studies showed that abnormal proα1(I) chains accumulated intracellularly in Aga2/+ dermal fibroblasts and were poorly secreted extracellularly. This was associated with the induction of an endoplasmic reticulum stress-specific unfolded protein response involving upregulation of BiP, Hsp47, and Gadd153 with caspases-12 and −3 activation and apoptosis of osteoblasts both in vitro and in vivo. These studies resulted in the identification of a new model for Osteogenesis imperfecta, and identified a role for intracellular modulation of the endoplasmic reticulum stress-associated unfolded protein response machinery toward osteoblast apoptosis during the pathogenesis of disease.

Osteogenesis imperfecta (OI) is a heterogeneous collection of connective tissue disorders typically caused by mutations in the COL1A1/2 genes that encode the chains of type I collagen, the principle structural protein of bone. Phenotypic expression in OI depends on the nature of the mutation, causing a clinical heterogeneity ranging from a mild risk of fractures to perinatal lethality. Here, we describe a new OI mouse model with a dominant mutation in the terminal C-propeptide domain of Col1a1 generated using the N-ethyl-N-nitrosourea (ENU) mutagenesis strategy. Heterozygous animals developed severe-to-lethal phenotypes that were associated with endoplasmic reticulum stress, and caspases-12 and −3 activation within calvarial osteoblasts. We provide evidence for endoplasmic reticulum stress–associated apoptosis as a key component in the pathogenesis of disease.

Diabetes models by screen for hyperglycemia in phenotype-driven ENU mouse mutagenesis projects

More than 150 million people suffer from diabetes mellitus worldwide, and this number is expected to rise substantially within the next decades. Despite its high prevalence, the pathogenesis of diabetes mellitus is not completely understood. Therefore, appropriate experimental models are essential tools to gain more insight into the genetics and pathogenesis of the disease. Here, we describe the current efforts to establish novel diabetes models derived from unbiased, phenotype-driven, large-scale N-ethyl-N-nitrosourea (ENU) mouse mutagenesis projects started a decade ago using hyperglycemia as a high-throughput screen parameter. Mouse lines were established according to their hyperglycemia phenotype over several generations, thereby revealing a mutation as cause for the aberrant phenotype. Chromosomal assignment of the causative mutation and subsequent candidate gene analysis led to the detection of the mutations that resulted in novel alleles of genes already known to be involved in glucose homeostasis, like glucokinase, insulin 2, and insulin receptor. Additional ENU-induced hyperglycemia lines are under genetic analysis. Improvements in screen for diabetic animals are implemented to detect more subtle phenotypes. Moreover, diet challenge assays are being employed to uncover interactions between genetic and environmental factors in the pathogenesis of diabetes mellitus. The new mouse mutants recovered in phenotype-driven ENU mouse mutagenesis projects complement the available models generated by targeted mutagenesis of candidate genes, all together providing the large resource of models required for a systematic dissection of the pathogenesis of diabetes mellitus.

Systemic overexpression of growth hormone (GH) in transgenic FVB/N inbred mice: an optimized model for holistic studies of molecular mechanisms underlying GH-induced kidney pathology

Transgenic mice overexpressing growth hormone (GH) display a plethora of phenotypic alterations and provide unique models for studying and influencing consequences of chronic GH excess. Since the first report on GH transgenic mice was published in 1982, many different mouse models overexpressing GH from various species at different levels and with different tissue specificities were established, most of them on random-bred or hybrid genetic background. We have generated a new transgenic mouse model on FVB/N inbred background, expressing bovine (b) GH under the control of the chicken beta-actin promoter (cbetaa). cbetaa-bGH transgenic mice exhibit ubiquitous expression of bGH mRNA and protein and circulating bGH levels in the range of several microg/ml, resulting in markedly stimulated growth and the characteristic spectrum of pathological lesions which were described in previous GH overexpressing mouse models. Importantly, a consistent sequence of renal alterations is observed, mimicking progressive kidney disease in human patients. The novel, genetically standardized GH transgenic mouse model is ideal for holistic transcriptome and proteome studies aiming at the identification of the molecular mechanisms underlying GH-induced pathological alterations especially in the kidney. Moreover, genetically defined cbetaa-bGH mice facilitate random mutagenesis screens for modifier genes which influence the effects of chronic GH excess and associated pathological lesions.

Screening for increased plasma urea levels in a large-scale ENU mouse mutagenesis project reveals kidney disease models

Kidney diseases lead to the failure of urinary excretion of metabolism products. In the Munich ethylnitrosourea (ENU) mouse mutagenesis project, which is done on a C3H inbred genetic background, blood samples of more than 15,000 G1 offspring and 500 G3 pedigrees were screened for alterations in clinical-chemical parameters. We identified 44 animals consistently exhibiting increased plasma urea concentrations. Transmission analysis of the altered phenotype of 23 mice to subsequent generations led to the establishment of five mutant lines. Both sexes were affected in these lines. Urinary urea levels were decreased in the mutants. In addition, most mutants showed increased plasma and decreased urinary creatinine levels. Pathological investigation of kidneys from the five mutant lines revealed a broad spectrum of alterations, ranging from no macroscopic and light microscopic kidney alterations to decreased kidney weight-to-body weight ratio, dilation of the renal pelvis, and severe glomerular lesions. Thus screening for elevated plasma urea levels in a large-scale ENU mouse mutagenesis project resulted in the successful establishment of mouse strains which are valuable tools for molecular studies of mechanisms involved in urea excretion or which represent interesting models for kidney diseases.

A genetic screen for modifiers of the delta1-dependent notch signaling function in the mouse

The Notch signaling pathway is an evolutionarily conserved transduction pathway involved in embryonic patterning and regulation of cell fates during development. Recent studies have demonstrated that this pathway is integral to a complex system of interactions, which are also involved in distinct human diseases. Delta1 is one of the known ligands of the Notch receptors. Mice homozygous for a loss-of-function allele of the Delta1 gene Dll1(lacZ/lacZ) die during embryonic development. Here, we present the results of two phenotype-driven modifier screens. Heterozygous Dll1(lacZ) knockout animals were crossed with ENU-mutagenized mice and screened for dysmorphological, clinical chemical, and immunological variants that are dependent on the Delta1 loss-of-function allele. First, we show that mutagenized heterozygous Dll1(lacZ) offspring have reduced body weight and altered specific clinical chemical parameters, including changes in metabolites and electrolytes relevant for kidney function. In our mutagenesis screen we have successfully generated 35 new mutant lines. Of major interest are 7 mutant lines that exhibit a Dll1(lacZ/+)-dependent phenotype. These mutant mouse lines provide excellent in vivo tools for studying the role of Notch signaling in kidney and liver function, cholesterol and iron metabolism, cell-fate decisions, and during maturation of T cells in the immune system.