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

Visuo-spatial learning and memory impairments in the 5xFAD mouse model of Alzheimer's disease: Effects of age, sex, albinism, and motor impairments

The 5xFAD mouse model of Alzheimer's disease (AD) rapidly develops AD-related neuro-behavioral pathology. Learning and memory impairments in 5xFAD mice, however, are not always replicated and the size of impairments varies considerably across studies. To examine possible sources of this variability, we analyzed the effects of age, sex, albinism due to background genes (Tyr^c , Oca2^p ) and motor impairment on learning and memory performance of wild type and 5xFAD mice on the Morris water maze, from 3 to 15 months of age. The 5xFAD mice showed impaired learning at 6-9 months of age, but memory impairments were not detected with the test procedure used in this study. Performance of 5xFAD mice was profoundly impaired at 12-15 months of age, but was accompanied by slower swim speeds than wild-type mice and a frequent failure to locate the escape platform. Overall female mice performed worse than males, and reversal learning impairments in 5xFAD mice were more pronounced in females than males. Albino mice performed worse than pigmented mice, confirming that albinism can impair performance of 5xFAD mice independently of AD-related transgenes. Overall, these results show that 5xFAD mice have impaired learning performance at 6-9 months of age, but learning and memory performance at 12-15 months is confounded with motor impairments. Furthermore, sex and albinism should be controlled to provide an accurate assessment of AD-related transgenes on learning and memory. These results will help reduce variability across pre-clinical experiments with 5xFAD mice, and thus enhance the reliability of studies developing new therapeutics for AD.

Embracing nature's complexity: Immunoparasitology in the wild

A wealth of research is dedicated to understanding how resistance against parasites is conferred and how parasite-driven pathology is regulated. This research is in part driven by the hope to better treatments for parasitic diseases of humans and livestock, and in part by immunologists who use parasitic infections as biomedical tools to evoke physiological immune responses. Much of the current mechanistic knowledge has been discovered in laboratory studies using model organisms, especially the laboratory mouse. However, wildlife are also hosts to a range of parasites. Through the study of host-parasite interactions in these non-laboratory systems we can gain a deeper understanding of parasite immunology in a more natural, complex environment. With a focus on helminth parasites, we here explore the insights gained into parasite-induced immune responses through (for immunologists) non-conventional experimental systems, and how current core findings from laboratory studies are reflected in these more natural conditions. The quality of the immune response is undoubtedly a central player in susceptibility versus resistance, as many laboratory studies have shown. Yet, in the wild, parasite infections tend to be chronic diseases. Whilst reading our review, we encourage the reader to consider the following questions which may (only) be answered by studying naturally occurring parasites in the wild: a) what type of immune responses are mounted against parasites in different hosts in the wild, and how do they vary within an individual over time, between individuals of the same species and between species? b) can we use wild or semi-wild study systems to understand the evolutionary drivers for tolerance versus resistance towards a parasite? c) what determines the ability of the host to cope with an infection and is there a link with the type of immune response mounted? d) can we modulate environmental factors to manipulate a wild animal's immune response to parasitic infections, with translation potential for humans, wildlife, and livestock? and e) in context of this special issue, what lessons for Type 2 immunity can we glean from studying animals in their natural environments? Further, we aim to integrate some of the knowledge gained in semi-wild and wild settings with knowledge gained from traditional laboratory-based research, and to raise awareness for the opportunities (and challenges) that come with integrating a multitude of naturally-occurring variables into immunoparasitological research.

The effect of background strain on the behavioral phenotypes of the MDGA2+/- mouse model of autism spectrum disorder

The membrane-associated mucin (MAM) domain containing glycosylphosphatidylinositol anchor 2 protein single knock-out mice (MDGA2^+/- ) are models of ASD. We examined the behavioral phenotypes of male and female MDGA2^+/- and wildtype mice on C57BL6/NJ and C57BL6/N backgrounds at 2 months of age and measured MDGA2, neuroligin 1 and neuroligin 2 levels at 7 months. Mice on the C57BL6/NJ background performed better than those on the C57BL6/N background in visual ability and in learning and memory performance in the Morris water maze and differed in measures of motor behavior and anxiety. Mice with the MDGA2^+/- genotype differed from WT mice in motor, social and repetitive behavior and anxiety, but most of these effects involved interactions between MDGA2^+/- genotype and background strain. The background strain also influenced MDGA2 levels and NLGN2 association in MDGA2^+/- mice. Our findings emphasize the importance of the background strain used in studies of genetically modified mice.

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.

EMX1 regulates NRP1-mediated wiring of the mouse anterior cingulate cortex

Transcription factors act during cortical development as master regulatory genes that specify cortical arealization and cellular identities. Although numerous transcription factors have been identified as being crucial for cortical development, little is known about their downstream targets and how they mediate the emergence of specific neuronal connections via selective axon guidance. The EMX transcription factors are essential for early patterning of the cerebral cortex, but whether EMX1 mediates interhemispheric connectivity by controlling corpus callosum formation remains unclear. Here, we demonstrate that in mice on the C57Bl/6 background EMX1 plays an essential role in the midline crossing of an axonal subpopulation of the corpus callosum derived from the anterior cingulate cortex. In the absence of EMX1, cingulate axons display reduced expression of the axon guidance receptor NRP1 and form aberrant axonal bundles within the rostral corpus callosum. EMX1 also functions as a transcriptional activator of Nrp1 expression in vitro, and overexpression of this protein in Emx1 knockout mice rescues the midline-crossing phenotype. These findings reveal a novel role for the EMX1 transcription factor in establishing cortical connectivity by regulating the interhemispheric wiring of a subpopulation of neurons within the mouse anterior cingulate cortex.

The Pathology of Aging 129S6/SvEvTac Mice

The 129 mouse strain is commonly used for the generation of genetically engineered mice. Genetic drift or accidental contamination during outcrossing has resulted in several 129 substrains. Comprehensive data on spontaneous age-related pathology exist for the 129S4/SvJae substrain, whereas only limited information is available for other 129 substrains. This longitudinal aging study describes the life span and spontaneous lesions of 44 male and 18 female mice of the 129S6/SvEvTac substrain. Median survival time was 778 and 770 days for males and females, respectively. Tumors of lung and Harderian gland were the most common neoplasms in both sexes. Hepatocellular tumors occurred mainly in males. Hematopoietic tumors were observed at low frequency. Suppurative and ulcerative blepharoconjunctivitis was the most common nonneoplastic condition in both sexes. Corynebacteria (primarily Corynebacterium urealyticum and C. pseudodiphtheriticum) were isolated from animals with blepharoconjunctivitis and in some cases from unaffected mice, although a clear causal association between corynebacterial infections and blepharoconjunctivitis could not be inferred. Polyarteritis occurred only in males and was identified as the most common nonneoplastic contributory cause of death. Eosinophilic crystalline pneumonia occurred in both sexes and was a relevant cause of death or comorbidity. Epithelial hyalinosis at extrapulmonary sites was noted at higher frequency in females. This study contributes important data on the spontaneous age-related pathology of the 129S6/SvEvTac mouse substrain and is a valuable reference for evaluation of the phenotype in genetically engineered mice obtained with this 129 substrain.

Hepatitis D Virus Infection of Mice Expressing Human Sodium Taurocholate Co-transporting Polypeptide

Hepatitis D virus (HDV) is the smallest virus known to infect human. About 15 million people worldwide are infected by HDV among those 240 million infected by its helper hepatitis B virus (HBV). Viral hepatitis D is considered as one of the most severe forms of human viral hepatitis. No specific antivirals are currently available to treat HDV infection and antivirals against HBV do not ameliorate hepatitis D. Liver sodium taurocholate co-transporting polypeptide (NTCP) was recently identified as a common entry receptor for HDV and HBV in cell cultures. Here we show HDV can infect mice expressing human NTCP (hNTCP-Tg). Antibodies against critical regions of HBV envelope proteins blocked HDV infection in the hNTCP-Tg mice. The infection was acute yet HDV genome replication occurred efficiently, evident by the presence of antigenome RNA and edited RNA species specifying large delta antigen in the livers of infected mice. The resolution of HDV infection appears not dependent on adaptive immune response, but might be facilitated by innate immunity. Liver RNA-seq analyses of HDV infected hNTCP-Tg and type I interferon receptor 1 (IFNα/βR1) null hNTCP-Tg mice indicated that in addition to induction of type I IFN response, HDV infection was also associated with up-regulation of novel cellular genes that may modulate HDV infection. Our work has thus proved the concept that NTCP is a functional receptor for HDV infection in vivo and established a convenient small animal model for investigation of HDV pathogenesis and evaluation of antiviral therapeutics against the early steps of infection for this important human pathogen.

Currently 15 million people worldwide are infected by hepatitis D virus (HDV). HDV is the smallest virus known to infect human. With co-infection of its helper hepatitis B virus (HBV), viral hepatitis D is considered as the most severe form of viral hepatitis. No specific anti-HDV drugs are available; antivirals against HBV do not ameliorate hepatitis D. We report mice expressing a human bile acids transporter sodium taurocholate co-transporting polypeptide (NTCP) in the liver support HDV infection, providing a useful model for studying antivirals against HDV and understanding how the simplest virus interacts with a host in vivo. Our transcriptome analyses of livers of infected mice have unveiled interaction landscape of HDV and the hosts, laying a foundation for further studies.

Expanding the mammalian phenotype ontology to support automated exchange of high throughput mouse phenotyping data generated by large-scale mouse knockout screens

BACKGROUND

A vast array of data is about to emerge from the large scale high-throughput mouse knockout phenotyping projects worldwide. It is critical that this information is captured in a standardized manner, made accessible, and is fully integrated with other phenotype data sets for comprehensive querying and analysis across all phenotype data types. The volume of data generated by the high-throughput phenotyping screens is expected to grow exponentially, thus, automated methods and standards to exchange phenotype data are required.

RESULTS

The IMPC (International Mouse Phenotyping Consortium) is using the Mammalian Phenotype (MP) ontology in the automated annotation of phenodeviant data from high throughput phenotyping screens. 287 new term additions with additional hierarchy revisions were made in multiple branches of the MP ontology to accurately describe the results generated by these high throughput screens.

CONCLUSIONS

Because these large scale phenotyping data sets will be reported using the MP as the common data standard for annotation and data exchange, automated importation of these data to MGI (Mouse Genome Informatics) and other resources is possible without curatorial effort. Maximum biomedical value of these mutant mice will come from integrating primary high-throughput phenotyping data with secondary, comprehensive phenotypic analyses combined with published phenotype details on these and related mutants at MGI and other resources.

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.