Evaluating mutant mice: anatomic pathology

Identification of vacuolar autophagic aggregates in the skeletal muscles of inbred C57BL/6NCrl mice

A comprehensive pathological analysis of inbred strains is essential to define strain-specific spontaneous lesions and to understand whether a specific phenotype results from experimental intervention or reflects a naturally occurring disease. This study aimed to report and describe a novel condition affecting the skeletal muscles of an inbred C57BL/6NCrl mouse colony characterised by large sarcoplasmic vacuoles in the muscle fibres of male mice in the subsarcolemmal spaces and the intermyofibrillary network. There was no muscle weakness, loss of ambulation or cardiac/respiratory involvement. Post-mortem evaluation and histological analysis excluded the presence of pathological accumulations or lesions in other tissues and organs. Changes were seen in fibre size, with many hypotrophic and some slightly hypertrophic fibres. Histological, immunohistochemical and molecular analyses of the vacuolar content revealed dysregulation of the autophagy machinery while ruling out a morphologically similar condition marked by the accumulation of tubular aggregates.

High Resolution Episcopic Microscopy for Qualitative and Quantitative Data in Phenotyping Altered Embryos and Adult Mice Using the New "Histo3D" System

3D imaging in animal models, during development or in adults, facilitates the identification of structural morphological changes that cannot be achieved with traditional 2D histological staining. Through the reconstruction of whole embryos or a region-of-interest, specific changes are better delimited and can be easily quantified. We focused here on high-resolution episcopic microscopy (HREM), and its potential for visualizing and quantifying the organ systems of normal and genetically altered embryos and adult organisms. Although the technique is based on episcopic images, these are of high resolution and are close to histological quality. The images reflect the tissue structure and densities revealed by histology, albeit in a grayscale color map. HREM technology permits researchers to take advantage of serial 2D aligned stacks of images to perform 3D reconstructions. Three-dimensional visualization allows for an appreciation of topology and morphology that is difficult to achieve with classical histological studies. The nature of the data lends itself to novel forms of computational analysis that permit the accurate quantitation and comparison of individual embryos in a manner that is impossible with histology. Here, we have developed a new HREM prototype consisting of the assembly of a Leica Biosystems Nanocut rotary microtome with optics and a camera. We describe some examples of applications in the prenatal and adult lifestage of the mouse to show the added value of HREM for phenotyping experimental cohorts to compare and quantify structure volumes. At prenatal stages, segmentations and 3D reconstructions allowed the quantification of neural tissue and ventricular system volumes of normal brains at E14.5 and E16.5 stages. 3D representations of normal cranial and peripheric nerves at E15.5 and of the normal urogenital system from stages E11.5 to E14.5 were also performed. We also present a methodology to quantify the volume of the atherosclerotic plaques of ApoEtm1Unc/tm1Unc mutant mice and illustrate a 3D reconstruction of knee ligaments in adult mice.

Major oscillations in spontaneous home-cage activity in C57BL/6 mice housed under constant conditions

The mouse is the most important mammalian model in life science research and the behavior of the mouse is a key read-out of experimental interventions and genetic manipulations. To serve this purpose a solid understanding of the mouse normal behavior is a prerequisite. Using 14-19 months of cumulative 24/7 home-cage activity recorded with a non-intrusive technique, evidence is here provided for a highly significant circannual oscillation in spontaneous activity (1-2 SD of the mean, on average 65% higher during peak of highs than lows; P = 7E-50) of male and female C57BL/6 mice held under constant conditions. The periodicity of this hitherto not recognized oscillation is in the range of 2-4 months (average estimate was 97 days across cohorts of cages). It off-sets responses to environmental stimuli and co-varies with the feeding behavior but does not significantly alter the preference for being active during the dark hours. The absence of coordination of this rhythmicity between cages with mice or seasons of the year suggest that the oscillation of physical activity is generated by a free-running intrinsic oscillator devoid of external timer. Due to the magnitude of this rhythmic variation it may be a serious confounder in experiments on mice if left unrecognized.

Challenges and Opportunities for the Veterinary Pathologist in Biomedical Research

Animal models have critical roles in biomedical research in promoting understanding of human disease and facilitating development of new therapies and diagnostic techniques to improve human and animal health. In the study of myriad human conditions, each model requires in-depth characterization of its assets and limitations in order for it to be used to greatest advantage. Veterinary pathology expertise is critical in understanding the relevance and translational validity of animal models to conditions under study, assessing morbidity and mortality, and validating outcomes as relevant or not to the study interventions. Clear communication with investigators and education of research personnel on the use and interpretation of pathology endpoints in animal models are critical to the success of any research program. The veterinary pathologist is underutilized in biomedical research due to many factors including misconceptions about high fiscal costs, lack of perceived value, limited recognition of their expertise, and the generally low number of veterinary pathologists currently employed in biomedical research. As members of the multidisciplinary research team, veterinary pathologists have an important role to educate scientists, ensure accurate interpretation of pathology data, maximize rigor, and ensure reproducibility to provide the most reliable data for animal models in biomedical research.

Pathology Principles and Practices for Analysis of Animal Models

Over 60% of NIH extramural funding involves animal models, and approximately 80% to 90% of these are mouse models of human disease. It is critical to translational research that animal models are accurately characterized and validated as models of human disease. Pathology analysis, including histopathology, is essential to animal model studies by providing morphologic context to in vivo, molecular, and biochemical data; however, there are many considerations when incorporating pathology endpoints into an animal study. Mice, and in particular genetically modified models, present unique considerations because these modifications are affected by background strain genetics, husbandry, and experimental conditions. Comparative pathologists recognize normal pathobiology and unique phenotypes that animals, including genetically modified models, may present. Beyond pathology, comparative pathologists with research experience offer expertise in animal model development, experimental design, optimal specimen collection and handling, data interpretation, and reporting. Critical pathology considerations in the design and use of translational studies involving animals are discussed, with an emphasis on mouse models.

Keeping Score: Semiquantitative and Quantitative Scoring Approaches to Genetically Engineered and Xenograft Mouse Models of Cancer

There is a growing need to quantitate or "score" lesions in mouse models of human disease, for correlation with human disease and to establish their clinical relevance. Several standard semiquantitative scoring schemes have been adapted for nonneoplastic lesions; similarly, the pathologist must carefully select an approach to score mouse models of cancer. Genetically engineered mouse models with a continuum of precancerous and cancerous lesions and xenogeneic models of various derivations present unique challenges for the pathologist. Important considerations include experimental design, understanding of the human disease being modeled, standardized classification of lesions, and approaches for semiquantitative and/or quantitative scoring in the model being evaluated. Quantification should be considered for measuring the extent of neoplasia and expression of tumor biomarkers. Semiquantitative scoring schemes have been devised that include severity, frequency, and distribution of lesions. Although labor-intensive, scoring mouse models of cancer provides numerical data that enable statistical analysis and greater translational impact.

A Spontaneous Missense Mutation in Branched Chain Keto Acid Dehydrogenase Kinase in the Rat Affects Both the Central and Peripheral Nervous Systems

A novel mutation, causing a phenotype we named frogleg because its most obvious characteristic is a severe splaying of the hind limbs, arose spontaneously in a colony of Sprague-Dawley rats. Frogleg is a complex phenotype that includes abnormalities in hind limb function, reduced brain weight with dilated ventricles and infertility. Using micro-satellite markers spanning the entire rat genome, the mutation was mapped to a region of rat chromosome 1 between D1Rat131 and D1Rat287. Analysis of whole genome sequencing data within the linkage interval, identified a missense mutation in the branched-chain alpha-keto dehydrogenase kinase (Bckdk) gene. The protein encoded by Bckdk is an integral part of an enzyme complex located in the mitochondrial matrix of many tissues which regulates the levels of the branched-chain amino acids (BCAAs), leucine, isoleucine and valine. BCAAs are essential amino acids (not synthesized by the body), and circulating levels must be tightly regulated; levels that are too high or too low are both deleterious. BCKDK phosphorylates Ser293 of the E1α subunit of the BCKDH protein, which catalyzes the rate-limiting step in the catabolism of the BCAAs, inhibiting BCKDH and thereby, limiting breakdown of the BCAAs. In contrast, when Ser293 is not phosphorylated, BCKDH activity is unchecked and the levels of the BCAAs will decrease dramatically. The mutation is located within the kinase domain of Bckdk and is predicted to be damaging. Consistent with this, we show that in rats homozygous for the mutation, phosphorylation of BCKDH in the brain is markedly decreased relative to wild type or heterozygous littermates. Further, circulating levels of the BCAAs are reduced by 70-80% in animals homozygous for the mutation. The frogleg phenotype shares important characteristics with a previously described Bckdk knockout mouse and with human subjects with Bckdk mutations. In addition, we report novel data regarding peripheral neuropathy of the hind limbs.

Optimization of heterologous DNA-prime, protein boost regimens and site of vaccination to enhance therapeutic immunity against human papillomavirus-associated disease

Background

Human papillomavirus (HPV) has been identified as the primary etiologic factor of cervical cancer as well as subsets of anogenital and oropharyngeal cancers. The two HPV viral oncoproteins, E6 and E7, are uniquely and consistently expressed in all HPV infected cells and are therefore promising targets for therapeutic vaccination. Both recombinant naked DNA and protein-based HPV vaccines have been demonstrated to elicit HPV-specific CD8+ T cell responses that provide therapeutic effects against HPV-associated tumor models. Here we examine the immunogenicity in a preclinical model of priming with HPV DNA vaccine followed by boosting with filterable aggregates of HPV 16 L2E6E7 fusion protein (TA-CIN).

Results

We observed that priming twice with an HPV DNA vaccine followed by a single TA-CIN booster immunization generated the strongest antigen-specific CD8+ T cell response compared to other prime-boost combinations tested in C57BL/6 mice, whether naïve or bearing the HPV16 E6/E7 transformed syngeneic tumor model, TC-1. We showed that the magnitude of antigen-specific CD8+ T cell response generated by the DNA vaccine prime, TA-CIN protein vaccine boost combinatorial strategy is dependent on the dose of TA-CIN protein vaccine. In addition, we found that a single booster immunization comprising intradermal or intramuscular administration of TA-CIN after priming twice with an HPV DNA vaccine generated a comparable boost to E7-specific CD8+ T cell responses. We also demonstrated that the immune responses elicited by the DNA vaccine prime, TA-CIN protein vaccine boost strategy translate into potent prophylactic and therapeutic antitumor effects. Finally, as seen for repeat TA-CIN protein vaccination, we showed that the heterologous DNA prime and protein boost vaccination strategy is well tolerated by mice.

Conclusions

Our results provide rationale for future clinical testing of HPV DNA vaccine prime, TA-CIN protein vaccine boost immunization regimen for the control of HPV-associated diseases.

Electronic supplementary material

The online version of this article (doi:10.1186/s13578-016-0080-z) contains supplementary material, which is available to authorized users.

Pathology of Mouse Models of Accelerated Aging

Progeroid mouse models display phenotypes in multiple organ systems that suggest premature aging and resemble features of natural aging of both mice and humans. The prospect of a significant increase in the global elderly population within the next decades has led to the emergence of "geroscience," which aims at elucidating the molecular mechanisms involved in aging. Progeroid mouse models are frequently used in geroscience as they provide insight into the molecular mechanisms that are involved in the highly complex process of natural aging. This review provides an overview of the most commonly reported nonneoplastic macroscopic and microscopic pathologic findings in progeroid mouse models (eg, osteoporosis, osteoarthritis, degenerative joint disease, intervertebral disc degeneration, kyphosis, sarcopenia, cutaneous atrophy, wound healing, hair loss, alopecia, lymphoid atrophy, cataract, corneal endothelial dystrophy, retinal degenerative diseases, and vascular remodeling). Furthermore, several shortcomings in pathologic analysis and descriptions of these models are discussed. Progeroid mouse models are valuable models for aging, but thorough knowledge of both the mouse strain background and the progeria-related phenotype is required to guide interpretation and translation of the pathology data.

Cause-of-Death Analysis in Rodent Aging Studies

In research studies using rats or mice, the cause of death is often not evaluated or reported. An analysis of the causes of death is particularly valuable for aging and carcinogenesis studies. Comparing causes of death among the study groups is often an important adjunct to the biochemical, molecular, clinical, and histopathologic findings. The methods for evaluating causes of death, contributing causes of death, and comorbidities have been suggested in several publications. Surprisingly, in important mouse aging studies, causes of death are often not reported. Cause-of-death assignment in preclinical rodent model aging research suffers from a lack of a standardized approach and an understanding of the value that it can add to longevity and interventional studies. While assigning single cause of death may facilitate data analysis, defining and publishing data on contributing causes (comorbidities) provides more information on associated underlying chronic conditions and health span in mouse models. This article reviews factors that affect determination of cause of death and the methods for evaluating causes of death and comorbidities. The proposed systematic pathology analysis includes assigning cause of death and comorbidities to define total disease burden. The combination of pathology with in vivo data will fully characterize the effect of tested interventions on multiple chronic diseases and health span of aging mice with improved translation to human aging and age-associated lesions.

Mouse Necropsy

Necropsy (also known as autopsy) is the post-mortem dissection of bodies after euthanasia or death and is a scientific examination conducted to observe and dissect the organs, collect tissues, and determine the extent of grossly evident disease. Research necropsies are conducted to obtain specific samples tailored according to study objectives. Diagnostic necropsy may be undertaken when unexpected illness or death occurs. The systematic collection of samples at necropsy is the critical first step in generating morphologic data from animal models. The morphologic (anatomic and histologic) data generates information on changes in cells, tissues, organs, and organ systems providing context for phenotypes (functional and morphological) to the level of the whole organism. Optimal insight into phenotype or pathophysiologic mechanisms is obtained when morphologic data is coupled with laboratory, medical, and molecular findings. This protocol provides a standard for an efficient routine mouse necropsy with brief comments on advanced or alternative techniques.

Safety studies of post-surgical buprenorphine therapy for mice

The use of appropriate analgesia in laboratory mice may be suboptimal because of concerns about adverse events (AE). Target Animal Safety trials were conducted to determine the safety of an extended-release suspension of buprenorphine. Drug or control suspensions were injected subcutaneously in surgically-treated BALB/c mice anesthetized with ketamine-xylazine to mimic post-operative conditions in which the compound might commonly be administered. Single and repeat five-fold (5×) excesses of the 3.25 mg/kg intended dose were used to provoke potential AE. Trials included prospective measurements of weight changes, blood chemistry, hematology, and histopathology. Clinical and histopathology findings were similar in drug-treated and control mice in a four-day trial using a single 16.25 mg/kg, 5× overdose of the drug. In a 12-day trial, which used a total buprenorphine dose of 48.75 mg/kg, clinical and histopathology values were also similar in control and drug-treated female mice. In the male arm of the repeat-overdose trial, two of eight mice died on the morning of day 12, three days following the third 16.25 mg/kg overdose administration. Histopathology did not reveal a cause of death. In a 14-month trial using a single 3.25 mg/kg dose of the drug, no significant findings identified potential AE. These findings indicate a high tolerance to an extended-release buprenorphine suspension administered post-operatively in mice with appropriate husbandry.

Pathobiology of aging mice and GEM: background strains and experimental design

The use of induced and spontaneous mutant mice and genetically engineered mice (and combinations thereof) to study cancers and other aging phenotypes to advance improved functional human life spans will involve studies of aging mice. Genetic background contributes to pathology phenotypes and to causes of death as well as to longevity. Increased recognition of expected phenotypes, experimental variables that influence phenotypes and research outcomes, and experimental design options and rationales can maximize the utility of genetically engineered mice (GEM) models to translational research on aging. This review aims to provide resources to enhance the design and practice of chronic and longevity studies involving GEM. C57BL6, 129, and FVB/N strains are emphasized because of their widespread use in the generation of knockout, transgenic, and conditional mutant GEM. Resources are included also for pathology of other inbred strain families, including A, AKR, BALB/c, C3H, C57L, C58, CBA, DBA, GR, NOD.scid, SAMP, and SJL/J, and non-inbred mice, including 4WC, AB6F1, Ames dwarf, B6, 129, B6C3F1, BALB/c,129, Het3, nude, SENCAR, and several Swiss stocks. Experimental strategies for long-term cross-sectional and longitudinal studies to assess causes of or contributors to death, disease burden, spectrum of pathology phenotypes, longevity, and functional healthy life spans (health spans) are compared and discussed.

Principles for valid histopathologic scoring in research

Histopathologic scoring is a tool by which semiquantitative data can be obtained from tissues. Initially, a thorough understanding of the experimental design, study objectives, and methods is required for the pathologist to appropriately examine tissues and develop lesion scoring approaches. Many principles go into the development of a scoring system such as tissue examination, lesion identification, scoring definitions, and consistency in interpretation. Masking (aka "blinding") of the pathologist to experimental groups is often necessary to constrain bias, and multiple mechanisms are available. Development of a tissue scoring system requires appreciation of the attributes and limitations of the data (eg, nominal, ordinal, interval, and ratio data) to be evaluated. Incidence, ordinal, and rank methods of tissue scoring are demonstrated along with key principles for statistical analyses and reporting. Validation of a scoring system occurs through 2 principal measures: (1) validation of repeatability and (2) validation of tissue pathobiology. Understanding key principles of tissue scoring can help in the development and/or optimization of scoring systems so as to consistently yield meaningful and valid scoring data.

A clinical frailty index in aging mice: comparisons with frailty index data in humans

We previously quantified frailty in aged mice with frailty index (FI) that used specialized equipment to measure health parameters. Here we developed a simplified, noninvasive method to quantify frailty through clinical assessment of C57BL/6J mice (5-28 months) and compared the relationship between FI scores and age in mice and humans. FIs calculated with the original performance-based eight-item FI increased from 0.06 ± 0.01 at 5 months to 0.36 ± 0.06 at 19 months and 0.38 ± 0.04 at 28 months (n = 14). By contrast, the increase was graded with a 31-item clinical FI (0.02 ± 0.005 at 5 months; 0.12 ± 0.008 at 19 months; 0.33 ± 0.02 at 28 months; n = 14). FI scores calculated from 70 self-report items from the first wave of the Survey of Health, Ageing and Retirement in Europe were plotted as function of age (n = 30,025 people). The exponential relationship between FI scores and age (normalized to 90% mortality) was similar in mice and humans for the clinical FI but not the eight-item FI. This noninvasive FI based on clinical measures can be used in longitudinal studies to quantify frailty in mice. Unlike the performance-based eight-item mouse FI, the clinical FI exhibits key features of the FI established for use in humans.

Neoplastic and Nonneoplastic Lesions in Aging Mice of Unique and Common Inbred Strains Contribution to Modeling of Human Neoplastic Diseases

The evaluation of spontaneous lesions in classical inbred strains of mice has become increasingly important because genetically engineered mice (GEMs) are created on these backgrounds. Novel inbred strains—genetically diverse from classic strains—are valuable both as a new background for GEM mice and to increase the genetic variation found in laboratory mice. Newly arising spontaneous genetic alterations in commonly used strains may also lead to new and valuable mouse models of disease. This report evaluates gross and histological lesions in relatively new, classic, and rarely explored mouse inbred strains. Pathological lesions of 1273 mice from 12 inbred strains (129S1/SvW, A.CA- H2f/W, AKR/W, BALB/cW, BN/aW, C57BL/6 W, C57BL/10 W, C3H/W, C3H wad/W, CBA/W, DBA/2 W, and WOM/W) are reported. BN/aW, WOM/W, and C3H wad/W are novel inbred strains produced and maintained in the Department of Genetics and Laboratory Animal Breeding at the Center of Oncology, Warsaw, Poland. Both neoplastic and nonneoplastic lesions were examined. The prevalence of lung neoplasms was significantly higher in A.CA- H2f/W (33.3%) and BALB/cW (33.8%) mice ( P < .01). The prevalence of liver neoplasms was significantly higher in the CBA/W strain ( P < .01). Mammary gland neoplasms arose at a greater frequency in C3H/W mice ( P < .01). The occurrence of uterine neoplasms was higher in DBA/W and 129S1/SvW mice. AKR/W and WOM/W mice developed T-cell lymphoblastic lymphoma with high frequency (110/121 [90.9%] and 159/175 [90.9%], respectively) before 1 year of age. The occurrence of nonneoplastic lesions in the kidneys of BN/aW mice was increased ( P < .01).

Pathology is a critical aspect of preclinical aging studies

Experimental design for mouse aging studies has historically involved lifespan, but it is now clear that survival data without pathology data limit the information that can be obtained on aging animals. This limitation becomes more serious when interventions of any sort are implemented. Pathology gives an insight into the health of an animal by revealing lesions not readily observable in the live animal. As such, it is a snapshot of disease conditions at the time of death. Therefore, a long-term goal is to establish pathology information as an essential component of studies involving health span and lifespan of aging animals. Given that pathology assessment is essential to help define the progression of lesions associated with aging, the real challenge is including it in aging studies because there is currently a lack of specialized expertise and resources. An increase in the level and scope of pathology assessment of tissues from old mice involved in aging studies is needed. A focus on the correlation of pathology data with longitudinal and cross-sectional lifespan data and health span physiology data can be established by enhancing standard histologic assessment of lesions observed in tissues from old mice. An environment for the development and integration of pathology data into aging studies of mice is needed to encourage more pathologists and other scientists to specialize in pathology of aging, and establish relevant standards to compare with other species including humans. Such results will have an important positive impact on aging studies because of the significant empowerment on data analyses and interpretation.

A phenotype survey of 36 mutant mouse strains with gene-targeted defects in glycosyltransferases or glycan-binding proteins

The consortium for functional glycomics (CFG) was a large research initiative providing networking and resources for investigators studying the role of glycans and glycan-binding proteins in health and disease. Starting in 2001, six scientific cores were established to generate data, materials and new technologies. By the end of funding in 2011, the mouse phenotype core (MPC) submitted data to a website from the phenotype screen of 36 mutant mouse strains deficient in a gene for either a glycan-binding protein (GBP) or glycosyltransferase (GT). Each mutant strain was allotted three months for analysis and screened by standard phenotype assays used in the fields of immunology, histology, hematology, coagulation, serum chemistry, metabolism and behavior. Twenty of the deficient mouse strains had been studied in other laboratories, and additional tests were performed on these strains to confirm previous observations and discover new data. The CFG constructed 16 new homozygous mutant mouse strains and completed the initial phenotype screen of the majority of these new mutant strains. In total, >300 phenotype changes were observed, but considering the over 100 assays performed on each strain, most of the phenotypes were unchanged. Phenotype differences include abnormal testis morphology in GlcNAcT9- and Siglec-H-deficient mice and lethality in Pomgnt1-deficient mice. The numerous altered phenotypes discovered, along with the consideration of the significant findings of normality, will provide a platform for future characterization to understand the important roles of glycans and GBPs in the mechanisms of health and disease.

A modified model of gentamicin induced renal failure in rats: toxicological effects of the iodinated X-ray contrast media ioversol and potential usefulness for toxicological evaluation of iodinated X-ray contrast media

Contrast-induced nephropathy (CIN) remains a serious complication in patients exposed to iodinated X-ray contrast media (ICM). Animal models of CIN are useful to further understand the mechanisms involved, identify novel biomarkers and evaluate potential differences between ICM. The current investigation was undertaken to modify the rat-gentamicin model for potential usefulness for toxicological evaluation of ICM. A dose-range finding study (50, 60 and 70 mg/kg body weight (bw)) of gentamicin was conducted over 4 consecutive days. Based on the kidney histopathology findings, a gentamicin dose of 70 mg/kg bw was chosen to investigate whether ICM would cause further renal damage. Following gentamicin treatment, this group was given a single administration of ioversol (6 gI/kg bw). Blood and urine samples were taken from all animals 3 days before the start of the study and at the end of treatment. Serum and urinary creatinine, urinary N-acetyl-β-D-glucosaminidase (NAG), γ-glutamyl transferase (GGT), total protein, and urine cytology were evaluated as biomarkers of renal damage. Histopathological examination of kidneys was performed. Histopathological examination of the kidneys revealed vacuolation, dilatation, and necrosis of the proximal tubules in the gentamicin-ioversol treatment group. These changes were not seen in the gentamicin-only treatment groups. Data on GGT and urinary epithelial cells show clear differences between rats treated with gentamicin alone versus gentamicin plus ioversol. These findings show that the modified rat-gentamicin model was able to demonstrate the nephrotoxic effect of ioversol.

3-dimensional imaging modalities for phenotyping genetically engineered mice

A variety of 3-dimensional (3D) digital imaging modalities are available for whole-body assessment of genetically engineered mice: magnetic resonance microscopy (MRM), X-ray microcomputed tomography (microCT), optical projection tomography (OPT), episcopic and cryoimaging, and ultrasound biomicroscopy (UBM). Embryo and adult mouse phenotyping can be accomplished at microscopy or near microscopy spatial resolutions using these modalities. MRM and microCT are particularly well-suited for evaluating structural information at the organ level, whereas episcopic and OPT imaging provide structural and functional information from molecular fluorescence imaging at the cellular level. UBM can be used to monitor embryonic development longitudinally in utero. Specimens are not significantly altered during preparation, and structures can be viewed in their native orientations. Technologies for rapid automated data acquisition and high-throughput phenotyping have been developed and continually improve as this exciting field evolves.

The gene or not the gene--that is the question: understanding the genetically engineered mouse phenotype

Embryonic stem cells have had a significant impact on understanding gene function and gene interactions through the use of genetically engineered mice. However, the genetic context (ie, mouse strain) in which these modifications in alleles are made may have a considerable effect on the phenotypic changes identified in these mice. In addition, tissue- and time-specific gene expression systems may generate unanticipated outcomes. This article discusses the history of embryonic stem cells, reviews how mouse strain can affect phenotype (using specific examples), and examines some of the caveats of conditional gene expression systems.

Designing phenotyping studies for genetically engineered mice

A phenotyping study records physiologic or morphologic changes in an experimental animal resulting from an intervention. In mice, this intervention is most frequently genetic, but it may be any type of experimental manipulation. Accurate representation of the human condition under study is essential if the model is to yield useful conclusions. In this review, general approaches to the design of phenotyping studies are considered. These approaches take into account major sources of reduced model validity, such as unexpected phenotypic variation in mice, evolutionary divergence between mice and humans, unanticipated sources of variation, and common design errors. As poor design is the most common reason why studies fail to yield enduring results, emphasis is placed on reduction of bias, sampling, controlled study design, and appropriate statistical analysis.

Internet and Print Resources to Facilitate Pathology Analysis When Phenotyping Genetically Engineered Rodents

Genetically engineered mice and rats are increasingly used as models for exploring disease progression and mechanisms. The full spectrum of anatomic, biochemical, and functional changes that develop in novel, genetically engineered mouse and rat lines must be cataloged before predictions regarding the significance of the mutation may be extrapolated to diseases in other vertebrate species, including humans. A growing list of reference materials, including books, journal articles, and websites, has been produced in the last 2 decades to assist researchers in phenotyping newly engineered rodent lines. This compilation provides an extensive register of materials related to the pathology component of rodent phenotypic analysis. In this article, the authors annotate the resources they use most often, to allow for quick determination of their relevance to research projects.

Practical pathology of aging mice

Old mice will have a subset of lesions as part of the progressive decline in organ function that defines aging. External and palpable lesions will be noted by the research, husbandry, or veterinary staff during testing, cage changing, or physical exams. While these readily observable lesions may cause alarm, not all cause undue distress or are life-threatening. In aging research, mice are maintained until near end of life that, depending on strain and genetic manipulation, can be upwards of 33 months. Aging research has unique welfare issues related to age-related decline, debilitation, fragility, and associated pain of chronic diseases. An effective aging research program includes the collaboration and education of the research, husbandry, and veterinary staff, and of the members of the institution animal care and use committee. This collaborative effort is critical to humanely maintaining older mice and preventing excessive censorship due to non-lethal diseases. Part of the educational process is becoming familiar with how old mice appear clinically, at necropsy and histopathologically. This baseline knowledge is important in making the determination of humane end points, defining health span, contributing causes of death and effects of interventions. The goal of this paper is to introduce investigators to age-associated diseases and lesion patterns in mice from clinical presentation to pathologic assessment. To do so, we present and illustrate the common clinical appearances, necropsy and histopathological lesions seen in subsets of the aging colonies maintained at the University of Washington.

Standardized Post-Mortem Examination and Fixation Procedures for Mutant and Treated Mice

A procedure for post-mortem examination (or necropsy) of mice is provided. The aim is to obtain a "holistic" picture of organs and systems at the anatomical and histological levels. The major issue is tissue preservation, which is achieved by rapid transfer into a fixative solution, usually neutral buffered formalin. Fixation is the first of the four basic steps in histopathological analyses of tissues, which also include embedding, sectioning, and staining. The protocols provided here describe routine methods for tissue fixation, as these methods are integral parts of any necropsy procedure. There is also a Strategic Planning section that addresses the overall approach to histopathological evaluation, as well as specifics such as age and gender of the mice, cohort size, and controls. Curr. Protoc. Mouse Biol. 1:17-53. © 2011 by John Wiley & Sons, Inc.

Mouse phenogenomics, toolbox for functional annotation of human genome

Mouse models are crucial for the functional annotation of human genome. Gene modification techniques including gene targeting and gene trap in mouse have provided powerful tools in the form of genetically engineered mice (GEM) for understanding the molecular pathogenesis of human diseases. Several international consortium and programs are under way to deliver mutations in every gene in mouse genome. The information from studying these GEM can be shared through international collaboration. However, there are many limitations in utility because not all human genes are knocked out in mouse and they are not yet phenotypically characterized by standardized ways which is required for sharing and evaluating data from GEM. The recent improvement in mouse genetics has now moved the bottleneck in mouse functional genomics from the production of GEM to the systematic mouse phenotype analysis of GEM. Enhanced, reproducible and comprehensive mouse phenotype analysis has thus emerged as a prerequisite for effectively engaging the phenotyping bottleneck. In this review, current information on systematic mouse phenotype analysis and an issue-oriented perspective will be provided.

Spontaneous Unilateral Brainstem Infarction in Swiss Mice

Spontaneous vestibular syndrome in mice, characterized clinically by head tilt, circling or rolling, can be caused by otitis media, arteritis or central nervous system lesions. Postmortem examination of eleven non-inbred Swiss mice submitted for necropsy due to acute onset of vestibular signs revealed lesions consistent with brainstem infarction. The lesions were characterized by unilateral, well-demarcated areas of necrosis, malacia, and gliosis, with variable amounts of hemorrhage, in the lateral aspect of the medulla and caudal pons. The affected area included the medial, lateral and superior vestibular nuclei, the facial nucleus and the spinal trigeminal nucleus. While vestibular disease secondary to otitis media, periarteritis, and central nervous system neoplasia has been reported in many mouse strains, these unilateral brainstem infarctions were only seen in Swiss mice. These lesions share features with Wallenberg's Lateral Medullary Syndrome, the most common type of brainstem infarct in humans.

Finfish and aquatic invertebrate pathology resources for now and the future

Utilization of finfish and aquatic invertebrates in biomedical research and as environmental sentinels has grown dramatically in recent decades. Likewise the aquaculture of finfish and invertebrates has expanded rapidly worldwide as populations of some aquatic food species and threatened or endangered aquatic species have plummeted due to overharvesting or habitat degradation. This increasing intensive culture and use of aquatic species has heightened the importance of maintaining a sophisticated understanding of pathology of various organ systems of these diverse species. Yet, except for selected species long cultivated in aquaculture, pathology databases and the workforce of highly trained pathologists lag behind those available for most laboratory animals and domestic mammalian and avian species. Several factors must change to maximize the use, understanding, and protection of important aquatic species: 1) improvements in databases of abnormalities across species; 2) standardization of diagnostic criteria for proliferative and nonproliferative lesions; and 3) more uniform and rigorous training in aquatic morphologic pathology.

Tissue collection for systematic phenotyping in the mouse

In this unit, a procedure for post-mortem examination of mice and tissue collection is provided. This procedure is performed for post-mortem analysis of anatomical defects (necropsy) and histological analysis and/or tissue collection destined for molecular biology applications. In both cases, tissue preservation is the major issue, but the way to achieve it depends on the objective. When histological analysis is the aim, tissue preservation is achieved by rapid transfer into fixative solutions. In contrast, molecular biology applications require rapid freezing of tissue samples to preserve mRNA integrity. Consequently, performing both procedures simultaneously may be at the expense of the final product quality.

'One medicine---one pathology': are veterinary and human pathology prepared?

The American Medical Association and the American Veterinary Medical Association have recently approved resolutions supporting 'One Medicine' or 'One Health' that bridge the two professions. The concept is far from novel. Rudolf Virchow, the Father of Modern Pathology, and Sir William Osler, the Father of Modern Medicine, were outspoken advocates of the concept. The concept in its modern iteration was re-articulated in the 1984 edition of Calvin Schwabe's 'Veterinary Medicine and Human Health.' The veterinary and medical pathology professions are steeped in a rich history of 'One Medicine,' but they have paradoxically parted ways, leaving the discipline of pathology poorly positioned to contribute to contemporary science. The time has come for not only scientists but also all pathologists to recognize the value in comparative pathology, the consequences of ignoring the opportunity and, most importantly, the necessity of preparing future generations to meet the challenge inherent in the renewed momentum for 'One Medicine.' The impending glut of new genetically engineered mice creates an urgent need for prepared investigators and pathologists.

Moderate reduction of gamma-secretase attenuates amyloid burden and limits mechanism-based liabilities

Although gamma-secretase is recognized as a therapeutic target for Alzheimer's disease, side effects associated with strong inhibition of this aspartyl protease raised serious concerns regarding this therapeutic strategy. However, it is not known whether moderate inhibition of this enzyme will allow dissociation of beneficial effects in the CNS from mechanism-based toxicities in the periphery. We tested this possibility by using a series of mice with genetic reduction of gamma-secretase (levels ranging from 25 to 64% of control mice). Here, we document that even 30% reduction of gamma-secretase can effectively ameliorate amyloid burden in the CNS. However, global reduction of this enzyme below a threshold level increased the risk of developing squamous cell carcinoma as well as abnormal proliferation of granulocytes in a gamma-secretase dosage-dependent manner. Importantly, we demonstrate that there exists a critical gamma-secretase level that reduces the risk of amyloidosis in the CNS and limits tumorigenesis in epithelia. Our findings suggest that moderate inhibition of gamma-secretase represents an attractive anti-amyloid therapy for Alzheimer's disease.

Epidermal growth factor receptor and notch pathways participate in the tumor suppressor function of gamma-secretase

Gamma-secretase, a unique aspartyl protease, is required for the regulated intramembrane proteolysis of Notch and APP, pathways that are implicated, respectively, in the pathogenesis of cancer and Alzheimer disease. However, the mechanism whereby reduction of gamma-secretase causes tumors such as squamous cell carcinoma (SCC) remains poorly understood. Here, we demonstrate that gamma-secretase functions in epithelia as a tumor suppressor in an enzyme activity-dependent manner. Notch signaling is down-regulated and epidermal growth factor receptor (EGFR) is activated in SCC caused by genetic reduction of gamma-secretase. Moreover, the level of EGFR is inversely correlated with the level of gamma-secretase in fibroblasts, suggesting that the up-regulation of EGFR stimulates hyperproliferation in epithelia of mice with genetic reduction of gamma-secretase. Supporting this notion is our finding that the proliferative response of fibroblasts lacking gamma-secretase activity is more sensitive when challenged by either EGF or an inhibitor of EGFR as ompared with wild type cells. Interestingly, the up-regulation of EGFR is independent of Notch signaling, suggesting that the EGFR pathway functions in parallel with Notch in the tumorigenesis of SCC. Collectively, our results establish a novel mechanism linking the EGFR pathway to the tumor suppressor role of gamma-secretase and that mice with genetic reduction of gamma-secretase represent an excellent rodent model for clarifying pathogenesis of SCC and for testing therapeutic strategy to ameliorate this type of human cancer.

Future directions in training veterinarians for careers in toxicological pathology in the United Kingdom

There is currently a global shortage of veterinary pathologists in all sectors of the discipline, and recruitment of toxicological pathologists is a particular problem for the pharmaceutical industry. Efforts to encourage veterinarians to consider alternative career paths to general practice must start at the undergraduate level, with provision of structured career guidance and strong role models from pathology and research disciplines. It is also imperative that both the importance of biomedical research and the role of animal models be clearly understood by both university staff and undergraduates. Traditionally, much post-graduate training in toxicological pathology is done "on the job" in the United Kingdom, but completion of a residency and/or PhD program is recognized as a good foundation for a career in industry and for successful completion of professional pathology examinations. New models of residency training in veterinary pathology must be considered in the United Kingdom to enable a more tailored approach to training toward specific career goals. A modular approach to residency training would allow core skills to be maintained, while additional training would target specific training requirements in toxicological pathology. Exposure to laboratory-animal pathology, toxicology, research methodology, and management skills would all be of benefit as an introduction to a career in toxicological pathology. However, long-term funding for UK residencies remains a problem that must be resolved if future recruitment needs in veterinary pathology are to be met.

Repair deficient mice reveal mABH2 as the primary oxidative demethylase for repairing 1meA and 3meC lesions in DNA

Two human homologs of the Escherichia coli AlkB protein, denoted hABH2 and hABH3, were recently shown to directly reverse 1-methyladenine (1meA) and 3-methylcytosine (3meC) damages in DNA. We demonstrate that mice lacking functional mABH2 or mABH3 genes, or both, are viable and without overt phenotypes. Neither were histopathological changes observed in the gene-targeted mice. However, in the absence of any exogenous exposure to methylating agents, mice lacking mABH2, but not mABH3 defective mice, accumulate significant levels of 1meA in the genome, suggesting the presence of a biologically relevant endogenous source of methylating agent. Furthermore, embryonal fibroblasts from mABH2-deficient mice are unable to remove methyl methane sulfate (MMS)-induced 1meA from genomic DNA and display increased cytotoxicity after MMS exposure. In agreement with these results, we found that in vitro repair of 1meA and 3meC in double-stranded DNA by nuclear extracts depended primarily, if not solely, on mABH2. Our data suggest that mABH2 and mABH3 have different roles in the defense against alkylating agents.

Cause and Effect Considerations in Diagnostic Pathology and Pathology Phenotyping of Genetically Engineered Mice (GEM)

Over the next several decades, biology is embarking on its most ambitious project yet: to annotate the human genome functionally, prioritizing and focusing on those genes relevant to development and disease. Model systems are fundamental prerequisites for this task, and genetically engineered mice (GEM) are by far the most accessible mammalian system because of their anatomical, physiological, and genetic similarity to humans. The scientific utility of GEM has become commonplace since the technology to produce them was established in the early 1980s. Conceptually, however, an efficiently coordinated high-throughput approach that permits correlation between newly discovered genes, functional properties of their protein products, and biological relevance of these products as drug targets has yet to be established. The discipline of veterinary anatomical pathology (hereafter referred to as pathology) is not immune to this requirement for evolution and adaptation, and to address relationships and tissue consequences between tens of thousands of genes and their cognate proteins, novel interdisciplinary technologies and approaches must emerge. Although many of the techniques of pathology are well established, in the context of pathology's contribution to functional annotation of the genome, several conceptually important and unresolved issues remain to be addressed. While an ever-increasing arsenal of genetic and molecular tool-sets are available to evaluate and understand the function of genes and their pathophysiological mechanisms, pathology will continue to play an essential role in confirming cause and effect relationships of gene function in development and disease. This role will continue to be dependent on keen observation, a systematic but disciplined approach, expert knowledge of strain-dependent anatomical differences and incidental lesions, and relevant tissue-based evidence. Miniaturization and high-throughput adaptation of these methods must also continue so that they can complement parallel phenotyping efforts, provide pathology-based data in pace with concurrent phenotyping efforts, and continue to find new utility in the collective effort of functional annotation.

Internet Resources for Phenotyping Engineered Rodents

Genetically engineered mice (GEM) and rats (GER) have emerged as the main mammalian models for investigating normal (physiological, or "health") and abnormal (patho-logical, or "disease") mechanisms. Regardless of the genetic manipulation, novel GEM and GER must undergo meticulous genotypic and phenotypic analyses before it is possible to predict the significance of the engineered gene with re-spect to health and disease, especially when the desire is to extrapolate the findings to humans. Numerous websites have been generated to give researchers additional tools to facilitate genotyping and phenotyping. This list of many extant sites with descriptions of their basic features provides a starting point for new and established scientists faced with the need to characterize a new GEM or GER model.

Ultrasound-guided left-ventricular catheterization: a novel method of whole mouse perfusion for microimaging

We describe a novel technique to perform whole-body perfusion fixation in mice with specific relevance to micro-imaging. With the guidance of high-frequency ultrasound imaging, we were able to perfuse fixative and contrast agents via a catheter inserted into the left ventricle, and therefore preserved the integrity of the chest and abdominal cavity. In this preliminary study, our success rate over 15 animals was 73%. We demonstrate applications of this technique for magnetic resonance imaging and micro-CT, but we expect that this method can be generally applied to whole-body perfusions of other small animals in which the intact body is necessary.

The state of the art of the zebrafish model for toxicology and toxicologic pathology research--advantages and current limitations

The zebrafish (Danio rerio) is now the pre-eminent vertebrate model system for clarification of the roles of specific genes and signaling pathways in development. The zebrafish genome will be completely sequenced within the next 1-2 years. Together with the substantial historical database regarding basic developmental biology, toxicology, and gene transfer, the rich foundation of molecular genetic and genomic data makes zebrafish a powerful model system for clarifying mechanisms in toxicity. In contrast to the highly advanced knowledge base on molecular developmental genetics in zebrafish, our database regarding infectious and noninfectious diseases and pathologic lesions in zebrafish lags far behind the information available on most other domestic mammalian and avian species, particularly rodents. Currently, minimal data are available regarding spontaneous neoplasm rates or spontaneous aging lesions in any of the commonly used wild-type or mutant lines of zebrafish. Therefore, to fully utilize the potential of zebrafish as an animal model for understanding human development, disease, and toxicology we must greatly advance our knowledge on zebrafish diseases and pathology.

Mouse-based phenogenomics for modelling human disease

The powerful and wide-ranging genetic tools available in the laboratory mouse make it the major experimental model for studying mammalian gene function in vivo and modelling human disease traits. Large-scale random mutagenesis approaches, either gene-driven or phenotype-driven, promise to identify new clinically relevant phenotypes and their associated genes. Development of appropriate tools for assessing clinical phenotypes in mice is a crucial component of these endeavours, as is the establishment of the infrastructure for archiving and distribution of the growing mutant resource to the community. Integrated, multidisciplinary programs will be needed to fully exploit the power of the mouse in molecular medicine.