Persistent mammary hyperplasia in FVB/N mice

The inbred FVB/N mouse strain is widely used for creating transgenic mice. Over the past decade, persistent mammary hyperplasia has been detected in many multiparous FVB/N female mice sent to the University of California, Davis (UCD) Mutant Mouse Pathology Laboratory (MMPL) by a number of different laboratories. However, the experimental details concerning most specimens were not always available. To confirm these empiric findings, experiments were carried out to evaluate the mammary glands of FVB/N mice under controlled conditions. Persistent mammary hyperplasia that related to parity was found. Weeks after their first to fourth pregnancy, 10 FVB/N female mice from the Lawrence Berkeley National Laboratory (LBNL) colony were studied and the mammary glands were evaluated. The percentage of fat pad filled was estimated, using image analysis. Serum samples and the pituitary gland from other FVB/N mice from the LBNL were assayed for prolactin concentration. Multiparous FVB/N females consistently had persistent mammary hyperplasia. Four of seven females in the LBNL colony had hyperplasia after three pregnancies. A few foci of squamous nodules and sporadic carcinomas also were observed. Thus, some FVB/N females may have persistent mammary hyperplasia after three pregnancies without detectable pituitary abnormalities. Mammary carcinomas also may develop sporadically. These background phenotypes must be considered when interpreting the effect of genetic manipulation in FVB/N mice.     

Development of electrocardiogram intervals during growth of FVB/N neonate mice

Background  

Electrocardiography remains the best diagnostic tool and therapeutic biomarker for a spectrum of pediatric diseases involving cardiac or autonomic nervous system defects. As genetic links to these disorders are established and transgenic mouse models produced in efforts to understand and treat them, there is a surprising lack of information on electrocardiograms (ECGs) and ECG abnormalities in neonate mice. This is likely due to the trauma and anaesthesia required of many legacy approaches to ECG recording in mice, exacerbated by the fragility of many mutant neonates. Here, we use a non-invasive system to characterize development of the heart rate and electrocardiogram throughout the growth of conscious neonate FVB/N mice.     

Compensated hypertrophy of cardiac ventricles in aged transgenic FVB/N mice overexpressing calsequestrin

Cardiac-specific overexpression of murine cardiac calsequestrin results in depressed contractile parameters and hypertrophy in transgenic mice. To determine the long-term consequences of calsequestrin overexpression, the cardiac phenotype of young (2–3-months old) and aged (17 months old) transgenic FVB/N mice was characterized. Ventricular/body weight ratios, which were increased in young transgenics compared with wild-types, were unaltered with age. Left atria of aged transgenics exhibited enlargement and mineralization, but their ventricles did not display fibrosis, mineralization and other injuries. Although echocardiography suggested a time-dependent change in ventricular geometry and loading conditions in vivo, as well as an age-dependent reduction of left ventricular fractional shortening in transgenic mice, Langendorff-perfused hearts of young and aged transgenics indicated that there were no age-related reductions of contractile parameters (±dP/dt). Furthermore, neither genotype nor age altered lung/body weight ratios. Thus, our findings suggest that left ventricular performance in calsequestrin overexpressing mice becomes apparently depressed with age, but this depression is not associated with progressive reduction of left ventricular contractility and heart failure.     

Squamous cell carcinomas of the skin at ear tag sites in aged FVB/N mice

We report the development of squamous cell carcinomas (SCCs) of the skin at or near the site of ear tags composed of a nickel-copper alloy and used for identification during the course of a long-term study of incipient congenic FVB/N mice containing the human BCL6 transgene (FVB.Cg-Tg[tetO-BCL6]Bbn Tg[EmicroSR-tTa]83Bop), their littermate controls, and wild-type FVB/N. Of a total population of 160 mice, 14 (8.8%) developed SCCs in the tagged (right) ear after a median observation period of 25 months, but none of the animals developed tumors in the opposite ear (P = 0.0001). Nine of the fourteen mice with SCCs had to be euthanized because they were thought to be in distress from the ear condition, but the remaining five died or were euthanized for other reasons related to the research study. These animals ranged in age from 331 to 921 days at the time of death. Five of the tumors were well-differentiated (grade 1) SCCs; the remainder were grade 3 and tended to be deeply invasive neoplasms with undifferentiated areas containing a spindle cell component. One of these metastasized to kidney. When using the FVB/N mouse strain for long-term studies, it is necessary to consider that nearly 9% of the population may develop SCCs at or near ear-tag sites that may necessitate early removal of the animal.     

Proteinuria of nonautoimmune origin in wild-type FVB/NJ mice

FVB/NJ mice frequently are used as transgenic hosts, but the suitability of this genetic background for transgenic and congenic models of systemic autoimmunity have not been reported. In this study, FVB/NJ mice were evaluated for the presence of serum autoantibodies and autoimmune kidney pathology. Previously unreported albuminuria was observed in aged female FVB/NJ mice; however, serum autoantibody testing, light microscopic evaluation of differentially stained renal sections, and evaluation of renal sections for immunoglobulin deposits revealed that the albuminuria was not of autoimmune etiology. Anecdotally, multiple characteristics of the FVB/NJ strain, including albuminuria, cholesterolemia, mild podocyte foot process effacement in aged female FVB/NJ kidneys and predisposition to enhanced Th2 immune responses, is reminiscent of human minimal change nephrotic syndrome (MCNS). We propose that mapping of genetic polymorphisms that are responsible for these traits in FVB/NJ mice may lead to increased understanding of mild nephrotic syndromes including MCNS and other proteinurias.     

The role of STAT transcription factors in apoptosis regulation of hypothalamic neurons in aging in HER-2/neu transgenic mice and wild-type FVB/N mice

For the firsts time, the involvement of the STAT pathway in the regulation of neuronal apoptosis in physiological aging and in old mice overexpressing the HER-2/neu oncogene was studied. We showed that suppression of STAT3, STAT5, and STAT6 and overexpression of the proapoptotic factor STAT1, which provides p53-mediated apoptosis, are the causes for increasing the number of apoptotic neurons in physiological aging. HER-2 tyrosine kinase receptor overexpression promotes neuronal survival through activation of STAT-signaling pathway with simultaneous suppression of the proapoptotic factor STAT1.     

Enzymes metabolizing xenobiotics in spontaneous tumors in mice

The microsomal monooxygenase activity in spontaneous mouse hepatomas has been studied. The cytochrome P-450 level in hepatomas was shown to be 2 times as low as that in the liver. The reduction of the cytochrome P-450 content in the tumour was accompanied by a decrease in the activity of benz(a)pyrene hydroxylase, amino-pyrene-N-demethylase and p-nitroanisole-O-demethylase. However, 7-ethoxycoumarin-O-deethylase activity in hepatomas was much higher than in the liver both estimated as mg of the microsomal protein and nmol of cytochrome P-450. The cytochrome b5 content in the hepatomas was comparable with its level in the liver. A more elevated content of NADPH-cytochrome c reductase and microsomal epoxide hydrolase activity was found in the hepatomas. The results obtained provide evidence of different oxidation effects regarding some substrates in the liver and hepatomas. The ratio of cytochrome P-450 isoforms is likely to change in the hepatomas in contrast with that in the liver.     

Differences in serotoninergic metabolism possibly contribute to differences in breathing phenotype of FVB/N and C57BL/6J mice

Mouse readiness for gene manipulation allowed the production of mutants with breathing defects reminiscent of breathing syndromes. As C57BL/6J and FVB/N inbred strains were often used as background strains for producing mutants, we compared their breathing pattern from birth onwards. At birth, in vivo and in vitro approaches revealed robust respiratory rhythm in FVB/N, but not C57BL/6J, neonates. With aging, rhythm robustness difference persisted, and interstrain differences in tidal volume, minute ventilation, breathing regulations, and blood-gas parameters were observed. As serotonin affected maturation and function of the medullary respiratory network, we examined the serotoninergic metabolism in the medulla of C57BL/6J and FVB/N neonates and aged mice. Interstrain differences in serotoninergic metabolism were observed at both ages. We conclude that differences in serotoninergic metabolism possibly contribute to differences in breathing phenotype of FVB/N and C57BL/6J mice.     

Mapping hyper-susceptibility to colitis-associated colorectal cancer in FVB/NJ mice

Inbred strains of mice differ in susceptibility to colitis-associated colorectal cancer (CA-CRC). We tested 10 inbred strains of mice for their response to azoxymethane/dextran sulfate sodium-induced CA-CRC and identified a bimodal inter-strain distribution pattern when tumor multiplicity was used as a phenotypic marker of susceptibility. The FVB/NJ strain was particularly susceptible showing a higher tumor burden than any other susceptible strains (12.5-week post-treatment initiation). FVB/NJ hyper-susceptibility was detected as early as 8-week post-treatment initiation with FVB/NJ mice developing 5.5-fold more tumors than susceptible A/J or resistant B6 control mice. Linkage analysis by whole genome scan in informative (FVB/NJ×C3H/HeJ)F2 mice identified a novel susceptibility locus designated as C olon c ancer s usceptibility 6 (Ccs6) on proximal mouse chromosome 6. When gender was used as a covariate, a LOD score of 5.4 was computed with the peak marker being positioned at rs13478727, 43.8 Mbp. Mice homozygous for FVB/NJ alleles at this locus had increased tumor multiplicity compared to homozygous C3H/HeJ mice. Positional candidates in this region of chromosome 6 were analyzed with respect to a possible role in carcinogenesis and a role in inflammatory response using a new epigenetic gene scoring tool (Myeloid Inflammation Score).     

Destructive Changes in the Neuronal Structure of the FVB/N Mouse Retina

We applied a series of selective antibodies for labeling the various cell types in the mammalian retina. These were used to identify the progressive loss of neurons in the FVB/N mouse, a model of early onset retinal degeneration produced by a mutation in the pde6b gene. The immunocytochemical studies, together with electroretinogram (ERG) recordings, enabled us to examine the time course of the degenerative changes that extended from the photoreceptors to the ganglion cells at the proximal end of the retina. Our study indicates that photoreceptors in FVB/N undergo a rapid degeneration within three postnatal weeks, and that there is a concomitant loss of retinal neurons in the inner nuclear layer. Although the loss of rods was detected at an earlier age during which time M- and S-opsin molecules were translocated to the cone nuclei; by 6 months all cones had also degenerated. Neuronal remodeling was also seen in the second-order neurons with horizontal cells sprouting processes proximally and dendritic retraction in rod-driven bipolar cells. Interestingly, the morphology of cone-driven bipolar cells were affected less by the disease process. The cellular structure of inner retinal neurons, i.e., ChAT amacrine cells, ganglion cells, and melanopsin-positive ganglion cells did not exhibit any gross changes of cell densities and appeared to be relatively unaffected by the massive photoreceptor degeneration in the distal retina. However, Muller cell processes began to express GFAP at their endfeet at p14, and it climbed progressively to the cell’s distal ends by 6 months. Our study indicates that FVB/N mouse provides a useful model with which to assess possible intervention strategies to arrest photoreceptor death in related diseases.     

Reorganization of horizontal cell processes in the developing FVB/N mouse retina

We investigated the morphological changes of horizontal cells after postnatal photoreceptor degeneration in the developing FVB/N mouse retina, using immunocytochemistry with anti-calbindin D-28K. From postnatal day 14 (P14) onwards, processes emerging from horizontal cells descend into the inner plexiform layer (IPL) and ramify mainly in stratum 1 of the IPL. Electron microscopy revealed that the descending processes make synaptic contacts with bipolar cells in the outer plexiform layer. Our results clearly demonstrate that loss of photoreceptor cells induces the reorganization of horizontal cell processes in the retinas of FVB/N mice as they mature.