Dose Fractionation During Puberty Is More Detrimental to Mammary Gland Development Than an Equivalent Acute Dose of Radiation Exposure.

PURPOSE: Computed tomographic (CT) scans in adolescents have increased dramatically in recent years. However, the effects of cumulative low-dose exposures on the development of radiation sensitive organs, such as the mammary gland, is unknown. The purpose of this work was to define the effects of dose rate on mammary organ formation during puberty, an especially sensitive window in mammary development. We used a fractionated low-dose x-ray exposure to mimic multiple higher dose CT scans, and we hypothesized that fractionated exposure would have less of an effect on the number of mammary gland defects compared with an acute exposure. METHODS AND MATERIALS: Female mice were subjected to fractionated low-dose x-ray exposure (10 cGy/d for 5 days), acute x-ray exposure (1 × 50 cGy), or sham exposure. As the wide genetic diversity in humans can play a role in a person's response to irradiation, 2 genetically diverse mouse strains differing in radiation sensitivity (BALB/c-sensitive; C57BL/6-resistant) were used to investigate the role of genetic background on the magnitude of the effect. RESULTS: Unexpectedly, our data reveal that multiple low-dose exposures produce greater immune and mammary defects for weeks after exposure compared with controls. The most pronounced defects being increased ductal branching in both strains and a greater percentage of terminal end buds in the BALB/c strain of mice exposed to fractionated radiation compared with sham. Radiation-induced defects near the terminal end bud were also increased in both strains. CONCLUSIONS: The findings suggest that fractionated low-dose exposures are potentially more damaging to organ development compared with an equivalent, single acute exposure and that genetic background is an important parameter modifying the severity of these effects.

Evaluation of skin irritation following weathered crude oil exposure in two mouse strains.

Petroleum crude oil spills are common and vary in size and scope. Spill response workers throughout the course of remediation are exposed to so-called weathered oil and are known to report diverse health effects, including contact dermatitis. A murine model of repeated exposure to weathered marine crude oil was employed utilizing two strains of mice, C57BL/6 and BALB/c, to investigate the pathology of this irritant and identify the principal hydrocarbon components deposited in skin. Histopathology demonstrated clear signs of irritation in oil-exposed skin from both mouse strains, characterized by prominent epidermal hyperplasia (acanthosis). BALB/c mice exposed to oil demonstrated more pronounced irritation compared with C57BL/6 mice, which was characterized by increased acanthosis as well as increased inflammatory cytokine/chemokine protein expression of IL-1ß, IL-6, CXCL10, CCL2, CCL3, CCL4, and CCL11. A gas chromatography/mass spectrometry method was developed for the identification and quantification of 42 aliphatic and EPA priority aromatic hydrocarbons from full thickness skin samples of C57BL/6 and BALB/c mice exposed to oil samples. Aromatic hydrocarbons were not detected in skin; however, aliphatic hydrocarbons in skin tended to accumulate with carbon numbers greater than C16. These preliminary data and observations suggest that weathered crude oil is a skin irritant and this may be related to specific hydrocarbon components, although immune phenotype appears to impact skin response as well.

Methylation silencing of TGF-ß receptor type II is involved in malignant transformation of esophageal squamous cell carcinoma.

BACKGROUND: Although massive studies have been conducted to investigate the mechanisms of esophageal squamous cell carcinoma (ESCC) carcinogenesis, the understanding of molecular alterations during the malignant transformation of epithelial dysplasia is still lacking, especially regarding epigenetic changes. RESULTS: To better characterize the methylation changes during the malignant transformation of epithelial dysplasia, a whole-genome bisulfite sequencing analysis was performed on a series of tumor, dysplastic, and non-neoplastic epithelial tissue samples from esophageal squamous cell carcinoma (ESCC) patients. Promoter hypermethylation in TGF-ß receptor type II (TGFBR2), an important mediator of TGF-ß signaling, was identified. Further, we evaluated the methylation and expression of TGFBR2 in tumor samples through The Cancer Genome Atlas multiplatform data as well as immunohistochemistry. Moreover, treatment of ESCC cell lines with5-Aza-2'-deoxycytidine, a DNA methyltransferase inhibitor, reactivated the expression of TGFBR2. The lentiviral mediating the overexpression of TGFBR2 inhibited the proliferation of ESCC cell line by inducing cell cycle G2/M arrest. Furthermore, the overexpression of TGFBR2 inhibited the tumor growth obviously in vivo. CONCLUSIONS: The characterization of methylation silencing of TGFBR2 in ESCC will enable us to further explore whether this epigenetic change could be considered as a predictor of malignant transformation in esophageal epithelial dysplasia and whether use of a TGFBR2 agonist may lead to a new therapeutic strategy in patients with ESCC.

BALB/c-congenic ANP32B-deficient mice reveal a modifying locus that determines viability.

We previously found that deletion of the multifunctional factor ANP32B (a.k.a. SSP29, APRIL, PAL31, PHAPI2) resulted in a severe but strain-specific defect resulting in perinatal lethality. The difficulty in generating an adult cohort of ANP32B-deficient animals limited our ability to examine adult phenotypes, particularly cancer-related phenotypes. We bred the Anp32b-null allele into the BALB/c and FVB/N genetic background. The BALB/c, but not the FVB/N, background provided sufficient frequency of adult Anp32b-null (Anp32b(-/-)) animals. From these, we found no apparent oncogenic role for this protein in mammary tumorigenesis contrary to what was predicted based on human data. We also found runtism, pathologies in various organ systems, and an unusual clinical chemistry signature in the adult Anp32b(-/-) mice. Intriguingly, genome-wide single-nucleotide polymorphism analysis suggested that our colony retained an unlinked C57BL/6J locus at high frequency. Breeding this locus to homozygosity demonstrated that it had a strong effect on Anp32b(-/-) viability indicating that this locus contains a modifier gene of Anp32b with respect to development. This suggests a functionally important genetic interaction with one of a limited number of candidate genes, foremost among them being the variant histone gene H2afv. Using congenic breeding strategies, we have generated a viable ANP32B-deficient animal in a mostly pure background. We have used this animal to reliably exclude mouse ANP32B as an important oncogene in mammary tumorigenesis. Our further phenotyping strengthens the evidence that ANP32B is a widespread regulator of gene expression. These studies may also impact the choice of subsequent groups with respect to congenic breeding versus de novo zygote targeting strategies for background analyses in mouse genetics.

Behavioral characterization of a model of differential susceptibility to obesity induced by standard and personalized cafeteria diet feeding.

Despite the increase in obesity prevalence over the last decades, humans show large inter-individual variability for susceptibility to diet-induced obesity. Understanding the biological basis of this susceptibility could identify new therapeutic alternatives against obesity. We characterized behavioral changes associated with propensity to obesity induced by cafeteria (CAF) diet consumption in mice. We show that Balb/c mice fed a CAF diet display a large inter-individual variability in susceptibility to diet-induced obesity, such that based on changes in adiposity we can classify mice as obesity prone (OP) or obesity resistant (OR). Both OP and OR were hyperphagic relative to control-fed mice but caloric intake was similar between OP and OR mice. In contrast, OR had a larger increase in locomotor activity following CAF diet compared to OP mice. Obesity resistant and prone mice showed similar intake of sweet snacks, but OR ate more savory snacks than OP mice. Two bottle sucrose preference tests showed that OP decreased their sucrose preference compared to OR mice after CAF diet feeding. Finally, to test the robustness of the OR phenotype in response to further increases in caloric intake, we fed OR mice with a personalized CAF (CAF-P) diet based on individual snack preferences. When fed a CAF-P diet, OR increased their calorie intake compared to OP mice fed the standard CAF diet, but did not reach adiposity levels observed in OP mice. Together, our data show the contribution of hedonic intake, individual snack preference and physical activity to individual susceptibility to obesity in Balb/c mice fed a standard and personalized cafeteria-style diet.

Experimental viral evolution to specific host MHC genotypes reveals fitness and virulence trade-offs in alternative MHC types.

The unprecedented genetic diversity found at vertebrate MHC (major histocompatibility complex) loci influences susceptibility to most infectious and autoimmune diseases. The evolutionary explanation for how these polymorphisms are maintained has been controversial. One leading explanation, antagonistic coevolution (also known as the Red Queen), postulates a never-ending molecular arms race where pathogens evolve to evade immune recognition by common MHC alleles, which in turn provides a selective advantage to hosts carrying rare MHC alleles. This cyclical process leads to negative frequency-dependent selection and promotes MHC diversity if two conditions are met: (i) pathogen adaptation must produce trade-offs that result in pathogen fitness being higher in familiar (i.e., host MHC genotype adapted to) vs. unfamiliar host MHC genotypes; and (ii) this adaptation must produce correlated patterns of virulence (i.e., disease severity). Here we test these fundamental assumptions using an experimental evolutionary approach (serial passage). We demonstrate rapid adaptation and virulence evolution of a mouse-specific retrovirus to its mammalian host across multiple MHC genotypes. Critically, this adaptive response results in trade-offs (i.e., antagonistic pleiotropy) between host MHC genotypes; both viral fitness and virulence is substantially higher in familiar versus unfamiliar MHC genotypes. These data are unique in experimentally confirming the requisite conditions of the antagonistic coevolution model of MHC evolution and providing quantification of fitness effects for pathogen and host. These data help explain the unprecedented diversity of MHC genes, including how disease-causing alleles are maintained.

Comparative gene expression analysis in mouse models for identifying critical pathways in mammary gland development.

Functional development of the mammary gland is an important physiological process. Several studies have used gene expression profiling of mammary gland development to identify the key genes in the process, but few focused on the involved pathways. And there is a lack of concordance between those observed pathways. In this article, we applied a standardized microarray preprocessing to four independent studies, and then used gene set enrichment analysis (GSEA) to identify the key pathways. The result demonstrated an increased concordance between these expression profiling data sets. From the stage of puberty to pregnancy, we found 7 up-regulated and 6 down-regulated pathways in common. From the period of pregnancy to lactation, we found 7 up-regulated and 58 down-regulated pathways in common. And 10 up-regulated and 3 down-regulated pathways were found in common from lactation to the involution period. The main canonical pathways identified belong to immune system, cell communication, metabolism, and disease-related pathways. Pathway analysis is a more effective method than single gene analysis because the former one can able to detect genes weakly connected to the phenotype. As we applied GSEA to the study, our findings suggested a greater concordance in this physiological process. The critical pathways we find can provide some insight of functional development of the mammary gland and motivate other relative studies.

Distinct role of T helper Type 17 immune response for Graves' hyperthyroidism in mice with different genetic backgrounds.

T helper type 17 (Th17) cells, a newly identified effector T-cell subset, have recently been shown to play a role in numerous autoimmune diseases, including iodine-induced autoimmune thyroiditis in non-obese diabetic (NOD)-H2(h4) mice, which had previously been thought Th1-dominant. We here studied the role of Th17 in Graves' hyperthyroidism, another thyroid-specific autoimmune disease, in a mouse model. Two genetically distinct BALB/c and NOD-H2(h4) strains with intact or disrupted IL-17 genes (IL-17(+/+) or IL-17(-/-)) were immunized with adenovirus (Ad) expressing the thyrotropin receptor (TSHR) A-subunit (Ad-TSHR289). Both IL-17(+/+) and IL-17(-/-) mice developed anti-TSHR antibodies and hyperthyroidism at equally high frequencies on the BALB/c genetic background. In contrast, some IL-17(+/+), but none of IL-17(-/-), mice became hyperthyroid on the NOD-H2(h4) genetic background, indicating the crucial role of IL-17 for development of Graves' hyperthyroidism in non-susceptible NOD-H2(h4), but not in susceptible BALB/c mice. In the T-cell recall assay, splenocytes and lymphocytes from the draining lymph nodes from either mouse strains, irrespective of IL-17 gene status, produced IFN-γ and IL-10 but not other cytokines including IL-17 in response to TSHR antigen. Thus, the functional significance of Th17 may not necessarily be predictable from cytokine expression patterns in splenocytes or inflammatory lesions. In conclusion, this is, to our knowledge, the first report showing that the role of Th17 cells for the pathogenesis of a certain autoimmune disease depends on the mouse genetic backgrounds.

Vanadium pentoxide induces pulmonary inflammation and tumor promotion in a strain-dependent manner.

BACKGROUND: Elevated levels of air pollution are associated with increased risk of lung cancer. Particulate matter (PM) contains transition metals that may potentiate neoplastic development through the induction of oxidative stress and inflammation, a lung cancer risk factor. Vanadium pentoxide (V2O5) is a component of PM derived from fuel combustion as well as a source of occupational exposure in humans. In the current investigation we examined the influence of genetic background on susceptibility to V2O5-induced inflammation and evaluated whether V2O5 functions as a tumor promoter using a 2-stage (initiation-promotion) model of pulmonary neoplasia in mice. RESULTS: A/J, BALB/cJ (BALB), and C57BL/6J (B6) mice were treated either with the initiator 3-methylcholanthrene (MCA; 10 microg/g; i.p.) or corn oil followed by 5 weekly aspirations of V2O5 or PBS and pulmonary tumors were enumerated 20 weeks following MCA treatment. Susceptibility to V2O5-induced pulmonary inflammation was assessed in bronchoalveolar lavage fluid (BALF), and chemokines, transcription factor activity, and MAPK signaling were quantified in lung homogenates. We found that treatment of animals with MCA followed by V2O5 promoted lung tumors in both A/J (10.3 +/- 0.9 tumors/mouse) and BALB (2.2 +/- 0.36) mice significantly above that observed with MCA/PBS or V2O5 alone (P < 0.05). No tumors were observed in the B6 mice in any of the experimental groups. Mice sensitive to tumor promotion by V2O5 were also found to be more susceptible to V2O5-induced pulmonary inflammation and hyperpermeability (A/J>BALB>B6). Differential strain responses in inflammation were positively associated with elevated levels of the chemokines KC and MCP-1, higher NFkappaB and c-Fos binding activity, as well as sustained ERK1/2 activation in lung tissue. CONCLUSIONS: In this study we demonstrate that V2O5, an occupational and environmentally relevant metal oxide, functions as an in vivo lung tumor promoter among different inbred strains of mice. Further, we identified a positive relationship between tumor promotion and susceptibility to V2O5-induced pulmonary inflammation. These findings suggest that repeated exposures to V2O5 containing particles may augment lung carcinogenesis in susceptible individuals through oxidative stress mediated pathways.

Intracerebellar transplantation of neural stem cells into mice with neurodegeneration improves neuronal networks with functional synaptic transmission.

Recent studies have shown that many kinds of stem cells are beneficial for patients suffering with neurodegenerative diseases. We investigated the effects of neural stem cell (NSC), Maudsley hippocampal clone 36 (MHP36) in the Niemann-Pick disease type C (NP-C) model mice. Herein, we demonstrate that MHP36 transplantation improves the neuropathological features without acute immune response and promotes neuronal networks with functional synaptic transmission. The number of surviving Purkinje neurons substantially increased in MHP36 transplanted NP-C mice compared with sham-transplanted NP-C mice. MHP36 significantly reduced both of astrocytic and microglial activations. We also found that these surviving Purkinje neurons have normal functional synapses with parallel fibers that have normal glutamate release probability in MHP36 transplanted NP-C mice. Furthermore, real-time PCR analysis revealed up-regulation of genes involved in both excitatory and inhibitory neurotransmission encoding subunits of the ionotropic glutamate receptors GluR2, 3 and GABAA receptor beta2. These findings suggest that NSC, MHP36 transplantation may have therapeutic effects in the treatment of NP-C and other neurodegenerative diseases.

Influence of mouse genetic background on wear particle-induced in vivo inflammatory osteolysis.

OBJECTIVE AND DESIGN: Genetics may influence wear particle-induced inflammatory osteolysis after joint replacement. In the present work, mice with three different genetic backgrounds were used to test this hypothesis. TREATMENT: C57BL/6J, Balb/c and Kunming mouse were used. Each kind of mouse was divided into those receiving 30 mg UHMWPE particle implantation onto the calvariae and those receiving a sham operation. METHODS: Mice of each group were sacrificed one week after surgery. Calvariae were harvested for immunological assay of TNF-alpha and IL-1 beta secretion in supernatants of calvariae organ culture and histological analysis of calvarial sagittal suture osteolysis and osteoclastogenesis. RESULTS: Although UHMWPE particles induced obvious calvarial sagittal suture osteolysis and osteoclastogenesis in all strains as compared with their corresponding control mice, the most significant change was found in C57BL/6J mice, less severe in Balb/c mice and much less severe in Kunming mice. In agreement with pathological findings, UHMWPE particles induced the highest IL-1 beta secretion in C57BL/6J mice, compared with Balb/c and Kunming mice. However, no difference was observed concerning TNF-alpha secretion among these mice. CONCLUSION: Our data suggests that genetics had a significant influence on wear particle-induced inflammation, osteoclastogenesis and osteolysis. The influence of genetic background on implant life in patients with joint replacement warrants further investigation.

Comparative study to elucidate the mechanism underlying the difference in airway hyperresponsiveness between two mouse strains.

The mechanism underlying airway hyperresponsiveness (AHR), a characteristic feature of asthma, remains obscure. We attempted to elucidate the mechanism responsible for the different degrees of AHR in two mouse strains, BALB/c and C57BL/6, following exposure to an anaphylactic trigger. When ovalbumin (OVA)-sensitized mice were challenged daily with OVA for up to three consecutive days, the BALB/c mice showed a higher degree of airway responsiveness to methacholine than did C57BL/6. Following the OVA challenge, eosinophils and macrophages in bronchoalveolar lavage fluid (BALF) from BALB/c increased significantly in number compared to those from C57BL/6. BALB/c mice also exhibited a higher serum IgE level than that of C57BL/6 after OVA challenge. The enhanced AHR and eosinophilic infiltration in BALF were significantly reduced by pretreatment with a selective cysteinyl-leukotriene type 1 receptor (cysLT(1)R) antagonist, montelukast. In the in vitro study, cysLT production was significantly lower in the dissected lung tissue from BALB/c than in tissue from C57BL/6 when both groups were stimulated with saline. The lungs from BALB/c generated significantly larger amounts of cysLTs on incubation with OVA rather than with saline, while the lungs from C57BL/6 did not show any significant increase in cysLTs with antigen stimulation. Significant upregulation of cysLT(1)R and cysLT(2)R mRNA expression was induced by OVA challenge in the lungs of BALB/c, but not in those of C57BL/6. It is suggested that, after an anaphylactic reaction, the degree of AHR is dependent on the genetic background and that cysLTs play an important role in the mechanism involved.

Relationships between early inflammatory response to bleomycin and sensitivity to lung fibrosis: a role for dipeptidyl-peptidase I and tissue inhibitor of metalloproteinase-3?

RATIONALE: Different sensitivities to profibrotic compounds such as bleomycin are observed among mouse strains. OBJECTIVES: To identify genetic factors contributing to the outcome of lung injury. METHODS: Physiological comparison of C57BL/6 (sensitive) and BALB/c (resistant) mice challenged by intratracheal bleomycin instillation revealed several early differences: global gene expression profiles were thus established from lungs derived from the two strains, in the absence of any bleomycin administration. MEASUREMENTS AND MAIN RESULTS: Expression of 25 genes differed between the two strains. Among them, two molecules, not previously associated with pulmonary fibrosis, were identified. The first corresponded to dipeptidyl-peptidase I (DPPI), a cysteine peptidase (also known as cathepsin C) essential for the activation of serine proteinases produced by immune/inflammatory cells. The second corresponded to tissue inhibitor of matrix metalloproteinase-3, which also inhibits members of the ADAM (a disintegrin and metalloproteinase) family, such as the tumor necrosis factor-converting enzyme. In functional studies performed in the bleomycin-induced lung fibrosis model, the level of expression of these two genes was closely correlated with specific early events associated with lung fibrosis, namely activation of polymorphonuclear neutrophil-derived serine proteases and tumor necrosis factor-alpha-dependent inflammatory syndrome. Surprisingly, genetic deletion of DPPI in the context of a C57BL/6 genetic background did not protect against bleomycin-mediated fibrosis, suggesting additional function(s) for this key enzyme. CONCLUSIONS: This study highlights the importance of the early inflammatory events that follow bleomycin instillation in the development of lung fibrosis, and describes for the first time the roles that DPPI and tissue inhibitor of matrix metalloproteinase-3 may play in this process.

IL-3 is an important differentiation factor for the development of prostaglandin E2-producing macrophages between C57BL/6 and BALB/c mice.

We have previously reported that peritoneal and splenic macrophages from Th2-dominant BALB/c mice produced higher amounts of prostaglandin (PG) E2 than cells from C57BL/6 mice. In this study, we investigated how macrophages from BALB/c mice acquire the ability of enhanced PGE2 production, using bone marrow-derived macrophages differentiated by M-CSF, GM-CSF or IL-3. There is no strain difference in PGE2 production by GM-CSF- and M-CSF-differentiated macrophages; however, IL-3-differentiated macrophages from BALB/c mice produced higher amounts of PGE2 and lower amounts of type I cytokines than cells from C57BL/6 mice. IL-3-differentiated macrophages from BALB/c mice expressed larger amounts of mRNA of membrane-bound (microsomal) PGE synthase-1 (mPGES-1). The amounts of PGE2 produced by macrophages were significantly reduced in mPGES-1-deficient mice, and these mice displayed enhanced Th1 responses after Propionibacterium acnes treatment compared with wild-type mice. Microarray analysis revealed 63 genes that are differentially expressed more than fivefold in macrophages between C57BL/6 and BALB/c mice. These results indicate that mPGES-1-mediated PGE2 produced by macrophages regulates immune responses, and IL-3 is an important factor for the differentiation of macrophages that produce higher amounts of PGE2 through mPGES-1 activity in BALB/c mice.

Balb/Cj male mice do not feminize after infection with larval Taenia crassiceps.

Balb/cJ mice fail to mount an immune response capable of clearing infection with larval Taenia crassiceps. Additionally, male Balb/cJ mice display a lag in larval growth of approximately 3 wk as compared to growth in female mice. It has been reported that male Balb/ cAnN mice generate a protective immune response early in infection, and become permissive to larval growth after they feminize (200-fold increase in serum estradiol and 90% decrease in serum testosterone). To determine if a different strain of Balb/c mice (Balb/cJ) also feminize, serum was collected from infected male mice for 16 wk and levels of 17-beta-estradiol and testosterone were measured via ELISA. In addition, the mounting responses of 12- and 16-wk infected male mice, as well as uninfected control mice, were determined after isolation with a female mouse. The results of these experiments show that male Balb/cJ mice do not feminize during infection with larval T. crassiceps. There was no significant change in serum levels of either 17-beta-estradiol or testosterone during the course of infection (> 16 wk). Moreover, there was no significant decrease in the number of times infected male mice mounted the female mouse as compared to uninfected controls. These results suggest that there may be variances between the substrains of Balb/c mice that lead to the phenotypic differences reported for male Balb/cJ and Balb/cAnN mice.

Mendelian analysis of a metastasis-prone substrain of BALB/c nude mice using a subcutaneously inoculated human tumour.

Most nude mice do not allow the formation of metastases after heterotransplantation of human malignant tumours. Here we describe a substrain of BALB/c nude mice (BALB/c/AnNCr) that reproducibly allows some human cancers to metastasize. By Mendelian analysis of hybrids between this substrain and C57BL/6J +/+ mice we found that the ability to allow a human tumour (MDA-MB-435 BAG) to express its metastatic phenotype is determined by a recessively inheritable trait in the mouse host. We are presently working to identify the genetics responsible for development of metastases. The study also includes immunohistochemical and electron microscopic analysis of the test tumour, originally assumed to be a human mammary carcinoma, but shown to possess characteristics of a malignant melanoma (1). The ultimate aim of our ongoing study is to establish a substrain of nude mice that will allow metastasis in all recipients.

PREDBALB/c: a system for the prediction of peptide binding to H2d molecules, a haplotype of the BALB/c mouse.

PRED(BALB/c) is a computational system that predicts peptides binding to the major histocompatibility complex-2 (H2(d)) of the BALB/c mouse, an important laboratory model organism. The predictions include the complete set of H2(d) class I (H2-K(d), H2-L(d) and H2-D(d)) and class II (I-E(d) and I-A(d)) molecules. The prediction system utilizes quantitative matrices, which were rigorously validated using experimentally determined binders and non-binders and also by in vivo studies using viral proteins. The prediction performance of PRED(BALB/c) is of very high accuracy. To our knowledge, this is the first online server for the prediction of peptides binding to a complete set of major histocompatibility complex molecules in a model organism (H2(d) haplotype). PRED(BALB/c) is available at http://antigen.i2r.a-star.edu.sg/predBalbc/.

Antigen-IgE desensitization in signal transducer and activator of transcription 6-deficient mast cells by suboptimal doses of antigen.

BACKGROUND: Rapid administration of suboptimal antigen induces transient unresponsiveness in patients with IgE antibodies to beneficial medications, but the molecular mechanisms of desensitization are poorly understood. Mast cells (MCs) have been implicated as the target cells. OBJECTIVE: To establish a physiologic model of IgE-antigen desensitization using mouse bone marrow-derived MCs (mBMMCs) from wild-type and signal transducer and activator of transcription 6 (STAT6)-deficient mice. METHODS: The mBMMCs were sensitized with dinitrophenyl (DNP) IgE or trinitrophenyl (TNP) IgE and activated with DNP/TNP-human serum albumin. For desensitization, suboptimal doses of DNP/TNP-human serum albumin were administered at fixed intervals. RESULTS: Desensitized mBMMCs failed to respond to an optimal dose of antigen, indicating successful desensitization. Desensitization was time dependent, with 5 minutes of antigen exposure being optimal. Resensitization with DNP-IgE did not reverse the process. The desensitized cells were responsive to calcium ionophore and phorbol myristate acetate. Thus, the desensitization reaction alters an early event in the high-affinity IgE receptor (FcepsilonRI)-dependent signaling pathway in a nontoxic manner. The mBMMCs from STAT6-null mice could not be desensitized by suboptimal doses of antigen. CONCLUSIONS: Mast cells can be rendered unresponsive by rapid administration of suboptimal doses of antigen in the presence of calcium, similar to in vivo desensitizations. The STAT6-null mBMMCs cannot be desensitized, providing the first molecular target in this inhibitory process.

Loss of heterozygosity occurs via mitotic recombination in Trp53+/- mice and associates with mammary tumor susceptibility of the BALB/c strain.

Loss of heterozygosity (LOH) occurs commonly in cancers causing disruption of tumor suppressor genes and promoting tumor progression. BALB/c-Trp53(+/-) mice are a model of Li-Fraumeni syndrome, exhibiting a high frequency of mammary tumors and other tumor types seen in patients. However, the frequency of mammary tumors and LOH differs among strains of Trp53(+/-) mice, with mammary tumors occurring only on a BALB/c genetic background and showing a high frequency of LOH, whereas Trp53(+/-) mice on a 129/Sv or (C57BL/6 x 129/Sv) mixed background have a very low frequency of mammary tumors and show LOH for Trp53 in only approximately 50% of tumors. We have performed studies on tumors from Trp53(+/-) mice of several genetic backgrounds to examine the mechanism of LOH in BALB/c-Trp53(+/-) mammary tumors. By Southern blotting, 96% (24 of 25) of BALB/c-Trp53(+/-) mammary tumors displayed LOH for Trp53. Karyotype analysis indicated that cells lacking one copy of chromosome 11 were present in all five mammary tumors analyzed but were not always the dominant population. Comparative genomic hybridization analysis of these five tumors indicated either loss or retention of the entire chromosome 11. Thus chromosome loss or deletions within chromosome 11 do not account for the LOH observed by Southern blotting. Simple sequence length polymorphism analysis of (C57BL/6 x BALB/c) F1-Trp53(+/-) mammary tumors showed that LOH occurred over multiple loci and that a combination of maternal and paternal alleles were retained, indicating that mitotic recombination is the most likely mechanism of LOH. Nonmammary tumors of BALB/c mice also showed a high frequency of LOH (22 of 26, 85%) indicating it was not a mammary tumor specific phenomenon but rather a feature of the BALB/c strain. In (C57BL/6 x BALB/c) F1-Trp53(+/-) mice LOH was observed in 93% (13 of 14) of tumors, indicating that the high frequency of LOH was a dominant genetic trait. Thus the high frequency of LOH for Trp53 in BALB/c-Trp53(+/-) mammary tumors occurs via mitotic recombination and is a dominant genetic trait that associates with the occurrence of mammary tumors in (C57BL/6 x BALB/c) F1-Trp53(+/-) mice. These results further implicate double-strand DNA break repair machinery as important contributors to mammary tumorigenesis.

A locus on mouse chromosome 6 that determines resistance to herpes simplex virus also influences reactivation, while an unlinked locus augments resistance of female mice.

During studies to determine a role for tumor necrosis factor (TNF) in herpes simplex virus type 1 (HSV-1) infection using TNF receptor null mutant mice, we discovered a genetic locus, closely linked to the TNF p55 receptor (Tnfrsf1a) gene on mouse chromosome 6 (c6), that determines resistance or susceptibility to HSV-1. We named this locus the herpes resistance locus, Hrl, and showed that it also mediates resistance to HSV-2. Hrl has at least two alleles, Hrl(r), expressed by resistant strains like C57BL/6 (B6), and Hrl(s), expressed by susceptible strains like 129S6 (129) and BALB/c. Although Hrl is inherited as an autosomal dominant gene, resistance to HSV-1 is strongly sex biased such that female mice are significantly more resistant than male mice. Analysis of backcrosses between resistant B6 and susceptible 129 mice revealed that a second locus, tentatively named the sex modifier locus, Sml, functions to augment resistance of female mice. Besides determining resistance, Hrl is one of several genes involved in the control of HSV-1 replication in the eye and ganglion. Remarkably, Hrl also affects reactivation of HSV-1, possibly by interaction with some unknown gene(s). We showed that Hrl is distinct from Cmv1, the gene that determines resistance to murine cytomegalovirus, which is encoded in the major NK cell complex just distal of p55 on c6. Hrl has been mapped to a roughly 5-centimorgan interval on c6, and current efforts are focused on obtaining a high-resolution map for Hrl.