A novel HSPB1S139F mouse model of Charcot-Marie-Tooth Disease.

Charcot-Marie-Tooth Disease (CMT) is a commonly inherited peripheral polyneuropathy. Clinical manifestations for this disease include symmetrical distal polyneuropathy, altered deep tendon reflexes, distal sensory loss, foot deformities, and gait abnormalities. Genetic mutations in heat shock proteins have been linked to CMT2. Specifically, mutations in the heat shock protein B1 (HSPB1) gene encoding for heat shock protein 27 (Hsp27) have been linked to CMT2F and distal hereditary motor and sensory neuropathy type 2B (dHMSN2B) subtype. The goal of the study was to examine the role of an endogenous mutation in HSPB1 in vivo and to define the effects of this mutation on motor function and pathology in a novel animal model. As sphingolipids have been implicated in hereditary and sensory neuropathies, we examined sphingolipid metabolism in central and peripheral nervous tissues in 3-month-old HspS139F mice. Though sphingolipid levels were not altered in sciatic nerves from HspS139F mice, ceramides and deoxyceramides, as well as sphingomyelins (SMs) were elevated in brain tissues from HspS139F mice. Histology was utilized to further characterize HspS139F mice. HspS139F mice exhibited no alterations to the expression and phosphorylation of neurofilaments, or in the expression of acetylated α-tubulin in the brain or sciatic nerve. Interestingly, HspS139F mice demonstrated cerebellar demyelination. Locomotor function, grip strength and gait were examined to define the role of HspS139F in the clinical phenotypes associated with CMT2F. Gait analysis revealed no differences between HspWT and HspS139F mice. However, both coordination and grip strength were decreased in 3-month-old HspS139F mice. Together these data suggest that the endogenous S139F mutation in HSPB1 may serve as a mouse model for hereditary and sensory neuropathies such as CMT2F.

CD70 Inversely Regulates Regulatory T Cells and Invariant NKT Cells and Modulates Type 1 Diabetes in NOD Mice.

The CD27-CD70 costimulatory pathway is essential for the full activation of T cells, but some studies show that blocking this pathway exacerbates certain autoimmune disorders. In this study, we report on the impact of CD27-CD70 signaling on disease progression in the NOD mouse model of type 1 diabetes (T1D). Specifically, our data demonstrate that CD70 ablation alters thymocyte selection and increases circulating T cell levels. CD27 signaling was particularly important for the thymic development and peripheral homeostasis of Foxp3+Helios+ regulatory T cells, which likely accounts for our finding that CD70-deficient NOD mice develop more-aggressive T1D onset. Interestingly, we found that CD27 signaling suppresses the thymic development and effector functions of T1D-protective invariant NKT cells. Thus, rather than providing costimulatory signals, the CD27-CD70 axis may represent a coinhibitory pathway for this immunoregulatory T cell population. Moreover, we showed that a CD27 agonist Ab reversed the effects of CD70 ablation, indicating that the phenotypes observed in CD70-deficient mice were likely due to a lack of CD27 signaling. Collectively, our results demonstrate that the CD27-CD70 costimulatory pathway regulates the differentiation program of multiple T cell subsets involved in T1D development and may be subject to therapeutic targeting.

Inactive rhomboid proteins RHBDF1 and RHBDF2 (iRhoms): a decade of research in murine models.

Rhomboid proteases, first discovered in Drosophila, are intramembrane serine proteases. Members of the rhomboid protein family that are catalytically deficient are known as inactive rhomboids (iRhoms). iRhoms have been implicated in wound healing, cancer, and neurological disorders such as Alzheimer's and Parkinson's diseases, inflammation, and skin diseases. The past decade of mouse research has shed new light on two key protein domains of iRhoms-the cytosolic N-terminal domain and the transmembrane dormant peptidase domain-suggesting new ways to target multiple intracellular signaling pathways. This review focuses on recent advances in uncovering the unique functions of iRhom protein domains in normal growth and development, growth factor signaling, and inflammation, with a perspective on future therapeutic opportunities.

Maternal and fetal alkaline ceramidase 2 is required for placental vascular integrity in mice.

Sphingolipids have been implicated in mammalian placental development and function, but their regulation in the placenta remains unclear. Herein we report that alkaline ceramidase 2 (ACER2) plays a key role in sustaining the integrity of the placental vasculature by regulating the homeostasis of sphingolipids in mice. The mouse alkaline ceramidase 2 gene (Acer2) is highly expressed in the placenta between embryonic day (E) 9.5 and E12.5. Acer2 deficiency in both the mother and fetus decreases the placental levels of sphingolipids, including sphingoid bases (sphingosine and dihydrosphingosine) and sphingoid base-1-phosphates (sphingosine-1-phosphate and dihydrosphingosine-1-phosphate) and results in the in utero death of ≈50% of embryos at E12.5 whereas Acer2 deficiency in either the mother or fetus has no such effects. Acer2 deficiency causes hemorrhages from the maternal vasculature in the junctional and/or labyrinthine zones in E12.5 placentas. Moreover, hemorrhagic but not non-hemorrhagic Acer2-deficient placentas exhibit an expansion of parietal trophoblast giant cells with a concomitant decrease in the area of the fetal blood vessel network in the labyrinthine zone, suggesting that Acer2 deficiency results in embryonic lethality due to the atrophy of the fetal blood vessel network in the placenta. Taken together, these results suggest that ACER2 sustains the integrity of the placental vasculature by controlling the homeostasis of sphingolipids in mice.

Lack of acute xenogeneic graft- versus-host disease, but retention of T-cell function following engraftment of human peripheral blood mononuclear cells in NSG mice deficient in MHC class I and II expression.

Immunodeficient mice engrafted with human peripheral blood mononuclear cells (PBMCs) support preclinical studies of human pathogens, allograft rejection, and human T-cell function. However, a major limitation of PBMC engraftment is development of acute xenogeneic graft- versus-host disease (GVHD) due to human T-cell recognition of murine major histocompatibility complex (MHC). To address this, we created 2 NOD- scid IL-2 receptor subunit γ ( IL2rg) null (NSG) strains that lack murine MHC class I and II [NSG-ß-2-microglobulin ( B2M) null ( IA IE)null and NSG -( Kb Db) null ( IAnull)]. We observed rapid human IgG clearance in NSG- B2Mnull ( IA IE) null mice whereas clearance in NSG -( Kb Db) null ( IAnull) mice and NSG mice was comparable. Injection of human PBMCs into both strains enabled long-term engraftment of human CD4+ and CD8+ T cells without acute GVHD. Engrafted human T-cell function was documented by rejection of human islet allografts. Administration of human IL-2 to NSG -( Kb Db) null ( IAnull) mice via adeno-associated virus vector increased human CD45+ cell engraftment, including an increase in human regulatory T cells. However, high IL-2 levels also induced the development of GVHD. These data document that NSG mice deficient in murine MHC support studies of human immunity in the absence of acute GVHD and enable evaluation of human antibody therapeutics targeting human T cells.-Brehm, M. A., Kenney, L. L., Wiles, M. V., Low, B. E., Tisch, R. M., Burzenski, L., Mueller, C., Greiner, D. L., Shultz, L. D. Lack of acute xenogeneic graft- versus-host disease, but retention of T-cell function following engraftment of human peripheral blood mononuclear cells in NSG mice deficient in MHC class I and II expression.

Identification of Acer2 as a First Susceptibility Gene for Lithium-Induced Nephrogenic Diabetes Insipidus in Mice.

BACKGROUND: Lithium, mainstay treatment for bipolar disorder, causes nephrogenic diabetes insipidus and hypercalcemia in about 20% and 10% of patients, respectively, and may lead to acidosis. These adverse effects develop in only a subset of patients treated with lithium, suggesting genetic factors play a role. METHODS: To identify susceptibility genes for lithium-induced adverse effects, we performed a genome-wide association study in mice, which develop such effects faster than humans. On day 8 and 10 after assigning female mice from 29 different inbred strains to normal chow or lithium diet (40 mmol/kg), we housed the animals for 48 hours in metabolic cages for urine collection. We also collected blood samples. RESULTS: In 17 strains, lithium treatment significantly elevated urine production, whereas the other 12 strains were not affected. Increased urine production strongly correlated with lower urine osmolality and elevated water intake. Lithium caused acidosis only in one mouse strain, whereas hypercalcemia was found in four strains. Lithium effects on blood pH or ionized calcium did not correlate with effects on urine production. Using genome-wide association analyses, we identified eight gene-containing loci, including a locus containing Acer2, which encodes a ceramidase and is specifically expressed in the collecting duct. Knockout of Acer2 led to increased susceptibility for lithium-induced diabetes insipidus development. CONCLUSIONS: We demonstrate that genome-wide association studies in mice can be used successfully to identify susceptibility genes for development of lithium-induced adverse effects. We identified Acer2 as a first susceptibility gene for lithium-induced diabetes insipidus in mice.

Alkaline ceramidase 2 is essential for the homeostasis of plasma sphingoid bases and their phosphates.

Sphingosine-1-phosphate (S1P) plays important roles in cardiovascular development and immunity. S1P is abundant in plasma because erythrocytes-the major source of S1P-lack any S1P-degrading activity; however, much remains unclear about the source of the plasma S1P precursor, sphingosine (SPH), derived mainly from the hydrolysis of ceramides by the action of ceramidases that are encoded by 5 distinct genes, acid ceramidase 1 ( ASAH1)/ Asah1, ASAH2/ Asah2, alkaline ceramidase 1 ( ACER1)/ Acer1, ACER2/ Acer2, and ACER3/ Acer3, in humans/mice. Previous studies have reported that knocking out Asah1 or Asah2 failed to reduce plasma SPH and S1P levels in mice. In this study, we show that knocking out Acer1 or Acer3 also failed to reduce the blood levels of SPH or S1P in mice. In contrast, knocking out Acer2 from either whole-body or the hematopoietic lineage markedly decreased the blood levels of SPH and S1P in mice. Of interest, knocking out Acer2 from whole-body or the hematopoietic lineage also markedly decreased the levels of dihydrosphingosine (dhSPH) and dihydrosphingosine-1-phosphate (dhS1P) in blood. Taken together, these results suggest that ACER2 plays a key role in the maintenance of high plasma levels of sphingoid base-1-phosphates-S1P and dhS1P-by controlling the generation of sphingoid bases-SPH and dhSPH-in hematopoietic cells.-Li, F., Xu, R., Low, B. E., Lin, C.-L., Garcia-Barros, M., Schrandt, J., Mileva, I., Snider, A., Luo, C. K., Jiang, X.-C., Li, M.-S., Hannun, Y. A., Obeid, L. M., Wiles, M. V., Mao, C. Alkaline ceramidase 2 is essential for the homeostasis of plasma sphingoid bases and their phosphates.

Development of Humanized Mice in the Age of Genome Editing.

Mice are the most commonly used model organisms to study human disease. Many genetic human diseases can be recapitulated by modifying the mouse genome allowing the testing of existing and novel therapeutics, including combinatorial therapeutics, without putting humans at risk. Specifically, the development of "humanized" mice, that is, severely immunodeficient mice engrafted with functional human hematopoietic and immune cells and tissues, has revolutionized our ability to study and model human diseases in preclinical in vivo systems. Until recently it has been challenging to develop strains of humanized mice with targeted mutations or that transgenically express human genes with site-specific mutations, and can permit optimal growth of functional human cells and tissues. However, recent advances in targeted nuclease-based genetic engineering have enabled precise modification and development of humanized mouse models at an unprecedented pace. These modifications permit optimal growth of functional human cells and tissues and can be used to replicate human genetically determined diseases. J. Cell. Biochem. 118: 3043-3048, 2017. © 2017 Wiley Periodicals, Inc.

Inhibitory G proteins play multiple roles to polarize sensory hair cell morphogenesis.

Inhibitory G alpha (GNAI or Gαi) proteins are critical for the polarized morphogenesis of sensory hair cells and for hearing. The extent and nature of their actual contributions remains unclear, however, as previous studies did not investigate all GNAI proteins and included non-physiological approaches. Pertussis toxin can downregulate functionally redundant GNAI1, GNAI2, GNAI3 and GNAO proteins, but may also induce unrelated defects. Here we directly and systematically determine the role(s) of each individual GNAI protein in mouse auditory hair cells. GNAI2 and GNAI3 are similarly polarized at the hair cell apex with their binding partner GPSM2, whereas GNAI1 and GNAO are not detected. In Gnai3 mutants, GNAI2 progressively fails to fully occupy the subcellular compartments where GNAI3 is missing. In contrast, GNAI3 can fully compensate for the loss of GNAI2 and is essential for hair bundle morphogenesis and auditory function. Simultaneous inactivation of Gnai2 and Gnai3 recapitulates for the first time two distinct types of defects only observed so far with pertussis toxin: 1) a delay or failure of the basal body to migrate off-center in prospective hair cells, and 2) a reversal in the orientation of some hair cell types. We conclude that GNAI proteins are critical for hair cells to break planar symmetry and to orient properly before GNAI2/3 regulate hair bundle morphogenesis with GPSM2.

Inhibitory G proteins play multiple roles to polarize sensory hair cell morphogenesis.

Inhibitory G alpha (GNAI or Gαi) proteins are critical for the polarized morphogenesis of sensory hair cells and for hearing. The extent and nature of their actual contributions remains unclear, however, as previous studies did not investigate all GNAI proteins and included non-physiological approaches. Pertussis toxin can downregulate functionally redundant GNAI1, GNAI2, GNAI3, and GNAO proteins, but may also induce unrelated defects. Here, we directly and systematically determine the role(s) of each individual GNAI protein in mouse auditory hair cells. GNAI2 and GNAI3 are similarly polarized at the hair cell apex with their binding partner G protein signaling modulator 2 (GPSM2), whereas GNAI1 and GNAO are not detected. In Gnai3 mutants, GNAI2 progressively fails to fully occupy the sub-cellular compartments where GNAI3 is missing. In contrast, GNAI3 can fully compensate for the loss of GNAI2 and is essential for hair bundle morphogenesis and auditory function. Simultaneous inactivation of Gnai2 and Gnai3 recapitulates for the first time two distinct types of defects only observed so far with pertussis toxin: (1) a delay or failure of the basal body to migrate off-center in prospective hair cells, and (2) a reversal in the orientation of some hair cell types. We conclude that GNAI proteins are critical for hair cells to break planar symmetry and to orient properly before GNAI2/3 regulate hair bundle morphogenesis with GPSM2.

Functional analysis of Collagen 17a1: A genetic modifier of junctional epidermolysis bullosa in mice.

Previous work strongly implicated Collagen 17a1 (Col17a1) as a potent genetic modifier of junctional epidermolysis bullosa (JEB) caused by a hypomorphic mutation (Lamc2jeb) in mice. The importance of the noncollagenous domain (NC4) of COLXVII was suggested by use of a congenic reduction approach that restricted the modifier effect to 2-3 neighboring amino acid changes in that domain. The current study utilizes TALEN and CRISPR/Cas9 induced amino acid replacements and in-frame indels nested to NC4 to further investigate the role of this and adjoining COLXVII domains both as modifiers and primary risk effectors. We confirm the importance of COLXVI AA 1275 S/G and 1277 N/S substitutions and utilize small nested indels to show that subtle changes in this microdomain attenuate JEB. We further show that large in-frame indels removing up to 1482 bp and 169 AA of NC6 through NC1 domains are surprisingly disease free on their own but can be very potent modifiers of Lamc2jeb/jeb JEB. Together these studies exploiting gene editing to functionally dissect the Col17a1 modifier demonstrate the importance of epistatic interactions between a primary disease-causing mutation in one gene and innocuous 'healthy' alleles in other genes.

Dystonin modifiers of junctional epidermolysis bullosa and models of epidermolysis bullosa simplex without dystonia musculorum.

The Lamc2jeb junctional epidermolysis bullosa (EB) mouse model has been used to demonstrate that significant genetic modification of EB symptoms is possible, identifying as modifiers Col17a1 and six other quantitative trait loci, several with strong candidate genes including dystonin (Dst/Bpag1). Here, CRISPR/Cas9 was used to alter exon 23 in mouse skin specific isoform Dst-e (Ensembl GRCm38 transcript name Dst-213, transcript ID ENSMUST00000183302.5, protein size 2639AA) and validate a proposed arginine/glutamine difference at amino acid p1226 in B6 versus 129 mice as a modifier of EB. Frame shift deletions (FSD) in mouse Dst-e exon 23 (Dst-eFSD/FSD) were also identified that cause mice carrying wild-type Lamc2 to develop a phenotype similar to human EB simplex without dystonia musculorum. When combined, Dst-eFSD/FSD modifies Lamc2jeb/jeb (FSD+jeb) induced disease in unexpected ways implicating an altered balance between DST-e (BPAG1e) and a rarely reported rodless DST-eS (BPAG1eS) in epithelium as a possible mechanism. Further, FSD+jeb mice with pinnae removed are found to provide a test bed for studying internal epithelium EB disease and treatment without severe skin disease as a limiting factor while also revealing and accelerating significant nasopharynx symptoms present but not previously noted in Lamc2jeb/jeb mice.

Programmable RNA-Guided Large DNA Transgenesis by CRISPR/Cas9 and Site-Specific Integrase Bxb1.

The inability to insert large DNA constructs into the genome efficiently and precisely is a key challenge in genomic engineering. Random transgenesis, which is widely used, lacks precision, and comes with a slew of drawbacks. Lentiviral and adeno-associated viral methods are plagued by, respectively, DNA toxicity and a payload capacity of less than 5 kb. Homology-directed repair (HDR) techniques based on CRISPR-Cas9 can be effective, but only in the 1-5 kb range. In addition, long homology arms-DNA sequences that permit construct insertion-of lengths ranging from 0.5 to 5 kb are required by currently known HDR-based techniques. A potential new method that uses Cas9-guided transposases to insert DNA structures up to 10 kb in length works well in bacteria, but only in bacteria. Surmounting these roadblocks, a new toolkit has recently been developed that combines RNA-guided Cas9 and the site-specific integrase Bxb1 to integrate DNA constructs ranging in length from 5 to 43 kb into mouse zygotes with germline transmission and into human cells. This ground-breaking toolkit will give researchers a valuable resource for developing novel, urgently needed mouse and human induced pluripotent stem cell (hiPSC) models of cancer and other genetic diseases, as well as therapeutic gene integration and biopharmaceutical applications, such as the development of stable cell lines to produce therapeutic protein products.

Efficient targeted transgenesis of large donor DNA into multiple mouse genetic backgrounds using bacteriophage Bxb1 integrase.

The development of mouse models of human disease and synthetic biology research by targeted transgenesis of large DNA constructs represent a significant genetic engineering hurdle. We developed an efficient, precise, single-copy integration of large transgenes directly into zygotes using multiple mouse genetic backgrounds. We used in vivo Bxb1 mediated recombinase-mediated cassette exchange (RMCE) with a transgene "landing pad" composed of dual heterologous Bxb1 attachment (att) sites in cis, within the Gt(ROSA)26Sor safe harbor locus. RMCE of donor was achieved by microinjection of vector DNA carrying cognate attachment sites flanking the donor transgene with Bxb1-integrase mRNA. This approach achieves perfect vector-free integration of donor constructs at efficiencies > 40% with up to ~ 43 kb transgenes. Coupled with a nanopore-based Cas9-targeted sequencing (nCATS), complete verification of precise insertion sequence was achieved. As a proof-of-concept we describe the development of C57BL/6J and NSG Krt18-ACE2 models for SARS-CoV2 research with verified heterozygous N1 animals within ~ 4 months. Additionally, we created a series of mice with diverse backgrounds carrying a single att site including FVB/NJ, PWK/PhJ, NOD/ShiLtJ, CAST/EiJ and DBA/2J allowing for rapid transgene insertion. Combined, this system enables predictable, rapid development with simplified characterization of precisely targeted transgenic animals across multiple genetic backgrounds.

Genetically diverse mouse platform to xenograft cancer cells.

The lack of genetically diverse preclinical animal models in basic biology and efficacy testing has been cited as a potential cause of failure in clinical trials. We developed and characterized five diverse RAG1 null mouse strains as models that allow xenografts to grow. In these strains, we characterized the growth of breast cancer, leukemia and glioma cell lines. We found a wide range of growth characteristics that were far more dependent on strain than tumor type. For the breast cancer cell line, we characterized the spectrum of xenograft/tumor growth at structural, histological, cellular and molecular levels across each strain, and found that each strain captures unique structural components of the stroma. Furthermore, we showed that the increase in tumor-infiltrating myeloid CD45+ cells and the amount of circulating cytokine IL-6 and chemokine KC (also known as CXCL1) is associated with a higher tumor size in different strains. This resource is available to study established human xenografts, as well as difficult-to-xenograft tumors and growth of hematopoietic stems cells, and to decipher the role of myeloid cells in the development of spontaneous cancers.

Functional humanization of immunoglobulin heavy constant gamma 1 Fc domain human FCGRT transgenic mice.

A major asset of many monoclonal antibody (mAb)-based biologics is their persistence in circulation. The MHC class I family Fc receptor, FCGRT, is primarily responsible for this extended pharmacokinetic behavior. Engagement of FCGRT with the crystallizable fragment (Fc) domain protects IgG from catabolic elimination, thereby extending the persistence and bioavailability of IgG and related Fc-based biologics. There is a need for reliable in vivo models to facilitate the preclinical development of novel IgG-based biologics. FcRn-humanized mice have been widely accepted as translationally relevant surrogates for IgG-based biologics evaluations. Although such FCGRT-humanized mice, especially the mouse strain, B6.Cg-Fcgrttm1Dcr Tg(FCGRT)32Dcr (abbreviated Tg32), have been substantially validated for modeling humanized IgG-based biologics, there is a recognized caveat - they lack an endogenous source of human IgG that typifies the human competitive condition. Here, we used CRISPR/Cas9-mediated homology-directed repair to equip the hFCGRT Tg32 strain with a human IGHG1 Fc domain. This replacement now results in mice that produce human IgG1 Fc-mouse IgG Fab2 chimeric antibodies at physiologically relevant levels, which can be further heightened by immunization. This endogenous chimeric IgG1 significantly dampens the serum half-life of administered humanized mAbs in an hFCGRT-dependent manner. Thus, such IgG1-Fc humanized mice may provide a more physiologically relevant competitive hFCGRT-humanized mouse model for the preclinical development of human IgG-based biologics.

Genes adapt to outsmart gene-targeting strategies in mutant mouse strains by skipping exons to reinitiate transcription and translation.

BACKGROUND: Gene disruption in mouse embryonic stem cells or zygotes is a conventional genetics approach to identify gene function in vivo. However, because different gene disruption strategies use different mechanisms to disrupt genes, the strategies can result in diverse phenotypes in the resulting mouse model. To determine whether different gene disruption strategies affect the phenotype of resulting mutant mice, we characterized Rhbdf1 mouse mutant strains generated by three commonly used strategies-definitive-null, targeted knockout (KO)-first, and CRISPR/Cas9. RESULTS: We find that Rhbdf1 responds differently to distinct KO strategies, for example, by skipping exons and reinitiating translation to potentially yield gain-of-function alleles rather than the expected null or severe hypomorphic alleles. Our analysis also revealed that at least 4% of mice generated using the KO-first strategy show conflicting phenotypes. CONCLUSIONS: Exon skipping is a widespread phenomenon occurring across the genome. These findings have significant implications for the application of genome editing in both basic research and clinical practice.

Improved mouse models and advanced genetic and genomic technologies for the study of neutrophils.

Mice have been excellent surrogates for studying neutrophil biology and, furthermore, murine models of human disease have provided fundamental insights into the roles of human neutrophils in innate immunity. The emergence of novel humanized mice and high-diversity mouse populations offers the research community innovative and powerful platforms for better understanding, respectively, the mechanisms by which human neutrophils drive pathogenicity, and how genetic differences underpin the variation in neutrophil biology observed among humans. Here, we review key examples of these new resources. Additionally, we provide an overview of advanced genetic engineering tools available to further improve such murine model systems, of sophisticated neutrophil-profiling technologies, and of multifunctional nanoparticle (NP)-based neutrophil-targeting strategies.

Loss of TRP53 (p53) accelerates tumorigenesis and changes the tumor spectrum of SJL/J mice.

Known as the guardian of the genome, transformation-related protein 53 (TRP53) is a well -known tumor suppressor. Here, we describe a novel TRP53 deficient mouse model on a tumor prone background-SJL/J mice. The absence of TRP53 (TRP53 nullizygosity) leads to a shift in the tumor spectrum from a non-Hodgkin's-like disease to thymic lymphomas and testicular teratomas at a very rapid tumor onset averaging ~12 weeks of age. In haplotype studies, comparing tumor prone versus tumor resistant Trp53 null mouse strains, we found that other tumor suppressor, DNA repair and/or immune system genes modulate tumor incidence in TRP53 null strains, suggesting that even a strong tumor suppressor such as TRP53 is modulated by genetic background. Due to their rapid development of tumors, the SJL/J TRP53 null mice generated here can be used as an efficient chemotherapy or immunotherapy screening mouse model.

Quantitative Trait Locus and Integrative Genomics Revealed Candidate Modifier Genes for Ectopic Mineralization in Mouse Models of Pseudoxanthoma Elasticum.

Pseudoxanthoma elasticum, a prototype of heritable multisystem ectopic mineralization disorders, is caused by mutations in the ABCC6 gene encoding a putative efflux transporter, ABCC6. The phenotypic spectrum of pseudoxanthoma elasticum varies, and the correlation between genotype and phenotype has not been established. To identify genetic modifiers, we performed quantitative trait locus analysis in inbred mouse strains that carry the same hypomorphic allele in Abcc6 yet with highly variable ectopic mineralization phenotypes of pseudoxanthoma elasticum. Abcc6 was confirmed as a major determinant for ectopic mineralization in multiple tissues. Integrative analysis using functional genomics tools that included GeneWeaver, String, and Mouse Genome Informatics identified a total of nine additional candidate modifier genes that could influence the organ-specific ectopic mineralization phenotypes. Integration of the candidate genes into the existing ectopic mineralization gene network expands the current knowledge on the complexity of the network that, as a whole, governs ectopic mineralization in soft connective tissues.