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.

Identification of FoxR2 as an oncogene in medulloblastoma

Medulloblastoma is the most common pediatric brain tumor, and in ∼25% of cases, it is driven by aberrant activation of the Sonic Hedgehog (SHH) pathway in granule neuron precursor (GNP) cells. In this study, we identified novel medulloblastoma driver genes through a transposon mutagenesis screen in the developing brain of wild-type and Trp53 mutant mice. Twenty-six candidates were identified along with established driver genes such as Gli1 and Crebbp. The transcription factor FoxR2, the most frequent gene identified in the screen, is overexpressed in a small subset of human medulloblastoma of the SHH subtype. Tgif2 and Alx4, 2 new putative oncogenes identified in the screen, are strongly expressed in the SHH subtype of human medulloblastoma. Mutations in these two genes were mutually exclusive with mutations in Gli1 and tended to cooccur, consistent with involvement in the SHH pathway. Notably, Foxr2, Tgif2, and Alx4 activated Gli-binding sites in cooperation with Gli1, strengthening evidence that they function in SHH signaling. In support of an oncogenic function, Foxr2 overexpression transformed NIH3T3 cells and promoted proliferation of GNPs, the latter of which was also observed for Tgif2 and Alx4. These findings offer forward genetic and functional evidence associating Foxr2, Tgif2, and Alx4 with SHH subtype medulloblastoma.

Mice carrying a hypomorphic Evi1 allele are embryonic viable but exhibit severe congenital heart defects

The ecotropic viral integration site 1 (Evi1) oncogenic transcription factor is one of a number of alternative transcripts encoded by the Mds1 and Evi1 complex locus (Mecom). Overexpression of Evi1 has been observed in a number of myeloid disorders and is associated with poor patient survival. It is also amplified and/or overexpressed in many epithelial cancers including nasopharyngeal carcinoma, ovarian carcinoma, ependymomas, and lung and colorectal cancers. Two murine knockout models have also demonstrated Evi1's critical role in the maintenance of hematopoietic stem cell renewal with its absence resulting in the death of mutant embryos due to hematopoietic failure. Here we characterize a novel mouse model (designated Evi1^fl3) in which Evi1 exon 3, which carries the ATG start, is flanked by loxP sites. Unexpectedly, we found that germline deletion of exon3 produces a hypomorphic allele due to the use of an alternative ATG start site located in exon 4, resulting in a minor Evi1 N-terminal truncation and a block in expression of the Mds1-Evi1 fusion transcript. Evi1^δex3/δex3 mutant embryos showed only a mild non-lethal hematopoietic phenotype and bone marrow failure was only observed in adult Vav-iCre/+, Evi1^fl3/fl3 mice in which exon 3 was specifically deleted in the hematopoietic system. Evi1^δex3/δex3 knockout pups are born in normal numbers but die during the perinatal period from congenital heart defects. Database searches identified 143 genes with similar mutant heart phenotypes as those observed in Evi1^δex3/δex3 mutant pups. Interestingly, 42 of these congenital heart defect genes contain known Evi1-binding sites, and expression of 18 of these genes are also effected by Evi1 siRNA knockdown. These results show a potential functional involvement of Evi1 target genes in heart development and indicate that Evi1 is part of a transcriptional program that regulates cardiac development in addition to the development of blood.

Role of Myc in hepatocellular proliferation and hepatocarcinogenesis

BACKGROUND & AIMS

Myc is involved in cell growth, proliferation, apoptosis, energy metabolism, and differentiation. Whether it is essential for hepatocellular proliferation and carcinogenesis is unclear due to a lack of an efficient hepatocyte-specific Myc disruption model. This study used a novel genetic model to investigate the involvement of Myc in hepatocellular proliferation and hepatocarcinogenesis in mice.

METHODS

Temporal hepatocyte-specific Myc disruption was achieved by use of the tamoxifen-inducible Cre-ER(T2) recombinase system under control of the serum albumin promoter. Hepatocyte proliferation was assessed by administering peroxisome proliferator-activated receptor α (PPARα) agonist Wy-14,643. A diethylnitrosamine-induced liver cancer model was used to evaluate the role of Myc in hepatocarcinogenesis.

RESULTS

Tamoxifen administration induced recombination of Myc specifically in hepatocytes of Myc(fl/fl,ERT2-Cre) mice. When treated with a known hepatocellular proliferative stimulus Wy-14,643, Myc(fl/fl,ERT2-Cre) mice showed a lower liver/body weight ratio and suppressed hepatocyte proliferation as compared to Myc(fl/fl) mice. Hepatic expression of cell cycle control genes, DNA repair genes, and Myc target gene miRNAs were upregulated in Wy-14,643-treated Myc(fl/fl) mouse livers, but not in Wy-14,643-treated Myc(fl/fl,ERT2-Cre) livers. However, no differences were observed in the lipid-lowering effect of Wy-14,643 between Myc(fl/fl,ERT2-Cre) and Myc(fl/fl) mice, consistent with no differences in the expression of several PPARα target genes involved in fatty acid β-oxidation. Moreover, when subjected to the diethylnitrosamine liver cancer bioassay, Myc(fl/fl,ERT2-Cre) mice exhibited a markedly lower incidence of tumor formation compared with Myc(fl/fl) mice.

CONCLUSIONS

Myc plays an essential role in hepatocellular proliferation and liver tumorigenesis.

Transposon mutagenesis identifies genes driving hepatocellular carcinoma in a chronic hepatitis B mouse model

The most common risk factor for developing hepatocellular carcinoma (HCC) is chronic infection with hepatitis B virus (HBV). To better understand the evolutionary forces driving HCC, we performed a near-saturating transposon mutagenesis screen in a mouse HBV model of HCC. This screen identified 21 candidate early stage drivers and a very large number (2,860) of candidate later stage drivers that were enriched for genes that are mutated, deregulated or functioning in signaling pathways important for human HCC, with a striking 1,199 genes being linked to cellular metabolic processes. Our study provides a comprehensive overview of the genetic landscape of HCC.

Sporadic naturally occurring melanoma in dogs as a preclinical model for human melanoma

Melanoma represents a significant malignancy in humans and dogs. Different from genetically engineered models, sporadic canine melanocytic neoplasms share several characteristics with human disease that could make dogs a more relevant preclinical model. Canine melanomas rarely arise in sun-exposed sites. Most occur in the oral cavity, with a subset having intra-epithelial malignant melanocytes mimicking the in situ component of human mucosal melanoma. The spectrum of canine melanocytic neoplasia includes benign lesions with some analogy to nevi, as well as invasive primary melanoma, and widespread metastasis. Growing evidence of distinct subtypes in humans, differing in somatic and predisposing germ-line genetic alterations, cell of origin, epidemiology, relationship to ultraviolet radiation and progression from benign to malignant tumors, may also exist in dogs. Canine and human mucosal melanomas appear to harbor BRAF, NRAS, and c-kit mutations uncommonly, compared with human cutaneous melanomas, although both species share AKT and MAPK signaling activation. We conclude that there is significant overlap in the clinical and histopathological features of canine and human mucosal melanomas. This represents opportunity to explore canine oral cavity melanoma as a preclinical model.

Proceedings of the 2013 National Toxicology Program Satellite Symposium

The 2013 annual National Toxicology Program (NTP) Satellite Symposium, entitled "Pathology Potpourri," was held in Portland, Oregon, in advance of the Society of Toxicologic Pathology's 32nd annual meeting. The goal of the NTP Symposium is to present current diagnostic pathology or nomenclature issues to the toxicologic pathology community. This article presents summaries of the speakers' presentations, including diagnostic or nomenclature issues that were presented, along with select images that were used for audience voting and discussion. Some lesions and topics covered during the symposium included a caudal tail vertebra duplication in mice; nephroblastematosis in rats; ectopic C cell tumor in a hamster; granular cell aggregates/tumor in the uterus of a hamster; Pneumocystis carinii in the lung of a rat; iatrogenic chronic inflammation in the lungs of control rats; hepatoblastoma arising within an adenoma in a mouse; humoral hypercalcemia of benignancy in a transgenic mouse; acetaminophen-induced hepatotoxicity in rats; electron microscopy images of iatrogenic intraerythrocytic inclusions in transgenic mice; questionable hepatocellular degeneration/cell death/artifact in rats; atypical endometrial hyperplasia in rats; malignant mixed Müllerian tumors/carcinosarcomas in rats; differential diagnoses of proliferative lesions of the intestine of rodents; and finally obstructive nephropathy caused by melamine poisoning in a rat.

Rodent intestinal epithelial carcinogenesis: pathology and preclinical models

Colon cancer is a major human malignancy that afflicts millions of people throughout the world each year. Genetics and diet play large roles in colon carcinogenesis although chemicals may also contribute. For the past 40 years, scientists have studied experimentally induced intestinal carcinogenesis in rodents in order to elucidate the etiology and mechanisms involved. Comparative histopathology has revealed many similarities of rodent and human intestinal cancers. Comparative molecular pathology has also shown genetic similarities. More recently, genetically engineered mice and inflammatory colon cancer models have been used for investigating mechanisms and potential chemopreventive and treatment modalities. This review will focus on comparative histopathology and nonclinical models.

Calcium lignosulphonate: re-evaluation of relevant endpoints to re-confirm validity and NOAEL of a 90-day feeding study in rats

A 90-day feeding study in Han/Wistar rats with calcium lignosulphonate was evaluated by the EFSA. The study was considered to be inadequate due to potentially impaired health status of the animals based upon a high incidence of minimal lymphoid hyperplasia in mesenteric/mandibular lymph nodes and Peyer's patches, and minimal lymphoid cell infiltration in the liver in all animals. The EFSA Panel further disagreed with the conclusion that the treatment-related observation of foamy histiocytosis in mesenteric lymph nodes was non-adverse and asked whether this observation would progress to something more adverse over time. A PWG was convened to assess the sections of lymph nodes, Peyer's patches and liver. In addition, all lymphoid tissues were re-examined. The clinical pathology and animal colony health screening data were re-evaluated. The question whether the foamy histiocytosis could progress to an adverse finding with increasing exposure duration was addressed by read-across. In conclusion, the animals on the 90-day feeding study were in good health, the study was adequate for safety evaluation, and the foamy histiocytes in the mesenteric lymph nodes were not considered adverse, but rather an adaptive response that was considered unlikely to progress to an adverse condition with time. The NOAEL was re-affirmed to be 2000 mg/kgbw/d.

Animal models of human prostate cancer: the consensus report of the New York meeting of the Mouse Models of Human Cancers Consortium Prostate Pathology Committee

Animal models, particularly mouse models, play a central role in the study of the etiology, prevention, and treatment of human prostate cancer. While tissue culture models are extremely useful in understanding the biology of prostate cancer, they cannot recapitulate the complex cellular interactions within the tumor microenvironment that play a key role in cancer initiation and progression. The National Cancer Institute (NCI) Mouse Models of Human Cancers Consortium convened a group of human and veterinary pathologists to review the current animal models of prostate cancer and make recommendations about the pathologic analysis of these models. More than 40 different models with 439 samples were reviewed, including genetically engineered mouse models, xenograft, rat, and canine models. Numerous relevant models have been developed over the past 15 years, and each approach has strengths and weaknesses. Analysis of multiple genetically engineered models has shown that reactive stroma formation is present in all the models developing invasive carcinomas. In addition, numerous models with multiple genetic alterations display aggressive phenotypes characterized by sarcomatoid carcinomas and metastases, which is presumably a histologic manifestation of epithelial-mesenchymal transition. The significant progress in development of improved models of prostate cancer has already accelerated our understanding of the complex biology of prostate cancer and promises to enhance development of new approaches to prevention, detection, and treatment of this common malignancy.

Abstract 1116: Sleeping Beauty mutagenesis identifies genes and pathways that cooperate with BrafV600E in melanoma initiation and progression

Malignant melanoma is a devastating disease the prevalence of which is on the rise. In humans, somatic mutation of BRAF, to encode the BRAFV600E oncoprotein, is an early predisposing event in melanoma initiation, but is insufficient to drive malignant melanomagenesis in the absence of additional cooperating events. We describe a genome-wide, forward genetic screen in mice restricted to pigment producing melanocytes as an unbiased approach to identify new candidate melanoma progression genes. By combining Sleeping Beauty (SB) with a Cre-activated BRafCA allele we observed frank melanomas with average latency of 36 weeks. By contrast, melanocyte specific expression of BRAFV600E elicited benign melanocytic nevi that failed to progress to malignant melanoma by one year of age. These findings confirm that SB mobilization altered genes that cooperate with BRAFV600E to promote melanoma progression. A discovery set of 1,200 statistically-defined candidate melanoma genes was identified from 70 SB|BRAFV600E tumors. Importantly, our screen identified seven SB mutated genes with human orthologs that are well established human melanoma drivers including: Cdkn2a, Pten, Gnaq, Mitf, Nf1, Rac1 and Ppp6c. Many biological signaling pathways and cellular processes were enriched for candidate melanoma genes altered in SB|BRAFV600E melanomas, including Wnt/Beta-catenin, TGFβ, PI3’-kinase and MAPK signaling pathways and biological processes regulating ubiquitin mediated proteolysis, tight junctions, cell cycle and axonal guidance. Integrated comparative oncogenomic analysis with human melanoma data sets provided a data-driven method to filter and prioritize candidate melanoma genes. The genes identified using the SB|BRAFV600E model may represent new human melanoma candidate cancer genes with potential clinical relevance to the progression and maintenance of human BRAF mutated melanoma.

Citation Format: Michael B. Mann, Michael A. Black, Jerrold M. Ward, Marcus W. Bosenberg, Martin McMahon, Cristin G. Print, David J. Adams, Neal G. Copeland, Nancy A. Jenkins. Sleeping Beauty mutagenesis identifies genes and pathways that cooperate with BrafV600E in melanoma initiation and progression. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1116. doi:10.1158/1538-7445.AM2013-1116

Estradiol differentially regulates calreticulin: a potential link with abnormal T cell function in systemic lupus erythematosus?

OBJECTIVE

Systemic lupus erythematosus (SLE) is an autoimmune disease that affects women nine times more often than men. The present study investigates estradiol-dependent control of the calcium-buffering protein, calreticulin, to gain further insight into the molecular basis of abnormal T cell signaling in SLE T cells.

METHODS

T cells were purified from blood samples obtained from healthy females and SLE patients. Calreticulin expression was quantified by real-time polymerase chain amplification. Calreticulin and estrogen receptor-α were co-precipitated and analyzed by Western blotting to determine if the proteins associate in T cells.

RESULTS

Calreticulin expression increased (p = 0.034) in activated control T cells, while estradiol decreased (p = 0.044) calreticulin in resting T cells. Calreticulin expression decreased in activated SLE T cell samples and increased in approximately 50% of resting T cell samples. Plasma estradiol was similar (p > 0.05) among SLE patients and control volunteers. Estrogen receptor-α and calreticulin co-precipitated from nuclear and cytoplasmic T cell compartments.

CONCLUSIONS

The results indicate that estradiol tightly regulates calreticulin expression in normal human T cells, and the dynamics are different between activated and resting T cells. The absence of this tight regulation in SLE T cells could contribute to abnormal T cell function.

Selenium and selenoprotein deficiencies induce widespread pyogranuloma formation in mice, while high levels of dietary selenium decrease liver tumor size driven by TGFα

Changes in dietary selenium and selenoprotein status may influence both anti- and pro-cancer pathways, making the outcome of interventions different from one study to another. To characterize such outcomes in a defined setting, we undertook a controlled hepatocarcinogenesis study involving varying levels of dietary selenium and altered selenoprotein status using mice carrying a mutant (A37G) selenocysteine tRNA transgene (Trsp(tG37) ) and/or a cancer driver TGFα transgene. The use of Trsp(tG37) altered selenoprotein expression in a selenoprotein and tissue specific manner and, at sufficient dietary selenium levels, separate the effect of diet and selenoprotein status. Mice were maintained on diets deficient in selenium (0.02 ppm selenium) or supplemented with 0.1, 0.4 or 2.25 ppm selenium or 30 ppm triphenylselenonium chloride (TPSC), a non-metabolized selenium compound. Trsp(tG37) transgenic and TGFα/Trsp(tG37) bi-transgenic mice subjected to selenium-deficient or TPSC diets developed a neurological phenotype associated with early morbidity and mortality prior to hepatocarcinoma development. Pathology analyses revealed widespread disseminated pyogranulomatous inflammation. Pyogranulomas occurred in liver, lungs, heart, spleen, small and large intestine, and mesenteric lymph nodes in these transgenic and bi-transgenic mice. The incidence of liver tumors was significantly increased in mice carrying the TGFα transgene, while dietary selenium and selenoprotein status did not affect tumor number and multiplicity. However, adenoma and carcinoma size and area were smaller in TGFα transgenic mice that were fed 0.4 and 2.25 versus 0.1 ppm of selenium. Thus, selenium and selenoprotein deficiencies led to widespread pyogranuloma formation, while high selenium levels inhibited the size of TGFα-induced liver tumors.

Deficiency of CCAAT/enhancer binding protein family DNA binding prevents malignant conversion of adenoma to carcinoma in NNK-induced lung carcinogenesis in the mouse

BACKGROUND

The CCAAT/enhancer binding proteins (C/EBPs) play important roles in carcinogenesis of many tumors including the lung. Since multiple C/EBPs are expressed in lung, the combinatorial expression of these C/EBPs on lung carcinogenesis is not known.

METHODS

A transgenic mouse line expressing a dominant negative A-C/EBP under the promoter of lung epithelial Clara cell secretory protein (CCSP) gene in doxycycline dependent fashion was subjected to 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced lung carcinogenesis bioassay in the presence and absence of doxycycline, and the effect of abolition of DNA binding activities of C/EBPs on lung carcinogenesis was examined.

RESULTS

A-C/EBP expression was found not to interfere with tumor development; however, it suppressed the malignant conversion of adenoma to carcinoma during NNK-induced lung carcinogenesis. The results suggested that Ki67 may be used as a marker for lung carcinomas in mouse.

CONCLUSIONS

The DNA binding of C/EBP family members can be used as a potential molecular target for lung cancer therapy.

The utility of immunohistochemistry for the identification of hematopoietic and lymphoid cells in normal tissues and interpretation of proliferative and inflammatory lesions of mice and rats

Expression of antigens in cells and tissues can be readily studied immunohistochemically with the use of antibodies. A panel of antibodies to cell-specific markers can be used to diagnose lesions, including tumors, in the hematopoietic and lymphoid systems. This review discusses the use of readily available antibodies and procedures to identify antigens expressed in normal tissues and in proliferative and inflammatory lesions in formalin-fixed, paraffin-embedded (FFPE) murine specimens.

Chemically exacerbated chronic progressive nephropathy not associated with renal tubular tumor induction in rats: an evaluation based on 60 carcinogenicity studies by the national toxicology program

Chronic progressive nephropathy (CPN) is a common age-related degenerative-regenerative disease of the kidney that occurs in both sexes of most strains of rats. Recently, claims have been made that enhanced CPN is a mode of action for chemically induced kidney tumors in male rats and that renal tubular tumors (RTTs) induced by chemicals that concomitantly exacerbate CPN are not relevant for human cancer risk assessments. Although CPN is an observable histopathological lesion that may be modified by diet, the etiology of this disease and the mechanisms for its exacerbation by chemicals are unknown, and it fails to meet fundamental principles for defining carcinogenic modes of action and human relevance. Our comprehensive evaluation of possible relationships between exacerbated CPN and induction of RTTs in 58 carcinogenicity studies, conducted by the National Toxicology Program, in male and 11 studies in female F344 rats using 60 chemicals revealed widespread inconsistency in the claimed association. Because the proposed hypothesis lacks evidence of biological plausibility, and due to inconsistent relationships between exacerbated CPN and kidney tumor incidence in carcinogenicity studies in rats, dismissing the human relevance of kidney tumors induced by chemicals that also exacerbate CPN in rats would be wrong.

Differentiation of rodent immune and hematopoietic system reactive lesions from neoplasias

The immune and hematopoietic systems play an important role in the normal homeostasis of blood and blood cells and for immune responses to endogenous and exogenous processes and insults. In order to interpret histopathologic changes in the immune and hematopoietic systems, it is important to understand the normal anatomy and histology of the thymus, spleen, lymph nodes, bone marrow, and other tissues. The thymus, spleen, and lymph nodes can be categorized by anatomical compartments, each of which contributes to specific immune functions. Lesions may be diagnosed by interpretive or descriptive (semiquantitative) methods. The interpretation of these tissues by lesion in anatomical compartments should allow for better understanding of these reactions and more definitive pathologic findings. Proliferative lesions may be difficult to differentiate from lymphomas and leukemias. The use of immunohistochemistry, compartmental pathology, and methods for the evaluation of clonality will make interpretation easier.

Training pathologists in mouse pathology

Expertise in the pathology of mice has expanded from traditional regulatory and drug safety screening (toxicologic pathology) primarily performed by veterinary pathologists to the highly specialized area of mouse research pathobiology performed by veterinary and medical pathologists encompassing phenotyping of mutant mice and analysis of research experiments exploiting inbred mouse strains and genetically engineered lines. With increasing use of genetically modified mice in research, mouse pathobiology and, by extension, expert mouse research-oriented pathologists have become integral to the success of basic and translational biomedical research. Training for today's research-oriented mouse pathologist must go beyond knowledge of anatomic features of mice and strain-specific background diseases to the specialized genetic nomenclature, husbandry, and genetics, including the methodology of genetic engineering and complex trait analysis. While training can be accomplished through apprenticeships in formal programs, these are often heavily service related and do not provide the necessary comprehensive training. Specialty courses and short-term mentoring with expert specialists are opportunities that, when combined with active practice and publication, will lead to acquisition of the skills required for cutting-edge mouse-based experimental science.

Pathology methods for the evaluation of embryonic and perinatal developmental defects and lethality in genetically engineered mice

The normal embryonic development of organs and other tissues in mice and all species is preprogrammed by genes. Inactivation of a gene involved in any stage of normal embryonic development can have severe consequences leading to embryonic or postnatal developmental defects and lethality. Pathology methods are reviewed for evaluating normal and abnormal placenta and embryo, especially after E12.5. These methods include pathology protocols for necropsy and histopathology in addition to references that will provide additional knowledge for embryo assessment including histology atlases and advanced embryo imaging techniques.

Proceedings of the 2011 National Toxicology Program Satellite Symposium

The 2011 annual National Toxicology Program (NTP) Satellite Symposium, entitled "Pathology Potpourri," was held in Denver, Colorado in advance of the Society of Toxicologic Pathology's 30th Annual Meeting. The goal of the NTP Symposium is to present current diagnostic pathology or nomenclature issues to the toxicologic pathology community. This article presents summaries of the speakers' presentations, including diagnostic or nomenclature issues that were presented, along with select images that were used for audience voting or discussion. Some lesions and topics covered during the symposium include: proliferative lesions from various fish species including ameloblastoma, gas gland hyperplasia, nodular regenerative hepatocellular hyperplasia, and malignant granulosa cell tumor; spontaneous cystic hyperplasia in the stomach of CD1 mice and histiocytic aggregates in the duodenal villous tips of treated mice; an olfactory neuroblastoma in a cynomolgus monkey; various rodent skin lesions, including follicular parakeratotic hyperkeratosis, adnexal degeneration, and epithelial intracytoplasmic accumulations; oligodendroglioma and microgliomas in rats; a diagnostically challenging microcytic, hypochromic, responsive anemia in rats; a review of microcytes and microcytosis; nasal lesions associated with green tea extract and Ginkgo biloba in rats; corneal dystrophy in Dutch belted rabbits; valvulopathy in rats; and lymphoproliferative disease in a cynomolgus monkey.

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.