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Gene targeting in C57BL/6 ES cells. Successful germ line transmission using recipient BALB/c blastocysts developmentally matured in vitro.

There are significant advantages to the production of gene-knockout mice directly in mouse strains other than 129. The availability now of ES cells derived from the C57BL/6 mouse strain presents workers with a valuable alternative. A major difficulty, however, is the requirement for BALB/c blastocysts as recipients for ES cell injection. Using standard procedures, few BALB/c blastocysts can be obtained. This limitation has now been resolved by harvesting BALB/c embryos at the early morula stage and maturing these to blastocysts by in vitro culture. Of early morulae harvested and cultured, over 70% were recovered as fully expanded and injectable blastocysts. C57BL/6 ES cell injection of these blastocysts has enabled the production of a number of gene-knockout mice with a success rate similar to that reported for ES cells derived from the 129 mouse strains.

Animals↗

Gene targeting approaches to analyzing hypertension.

Essential hypertension probably results from combinations of small genetic variations that are partly normal variations and may not be appreciably harmful individually. Strategies to identify genes contributing to hypertension are discussed in this review. Gene targeting approaches, especially gene titration, have been used in these studies of hypertension. Gene titration experiments vary the expression of a chosen gene product by generating animals having different numbers of copies of the gene coding for the product. Gene titration is powerful for analyzing quantitative variations seen in common polygenic disorders, such as kidney diseases, diabetes mellitus, and atherosclerosis, as well as hypertension, because it allows tests of causation by determining the effects on a phenotype by changes in expression of the altered gene and because it matches normal quantitative variations more closely than is possible with classic transgenic mice. The use of zero-copy (gene "knockout") animals generated by gene disruption for studies of qualitative gene effects is also discussed. These various gene targeting experiments help identify genes regulating BP, promote a better understanding of the pathophysiology of the condition, and help identify potential targets for therapies.

Animals↗

Animal models of xenobiotic receptors.

Retinoid X receptors (RXRs) form heterodimers with pregnane X receptor (PXR) and constitutive androstane receptor (CAR), two prototypical xenobiotic receptors, and mediate metabolism of xenobiotics (foreign compounds) and endobiotics (endogenous compounds). Establishment of gene knockout and transgenic mouse models of RXRs, PXR, and CAR greatly enhanced the study of the biology of nuclear receptors, leading to considerable research progress in understanding the molecular mechanism underlying the nuclear receptor-mediated pathways in xenobiotic and endobiotic metabolism. These animal models are widely used in screening nuclear receptor ligands, identifying nuclear receptor target genes, and defining physiological and pharmacological pathways mediated by these xenobiotic nuclear receptors. In addition, "humanized" PXR and CAR mouse models, which avoid species specificity, provide valuable tools for investigating human xenobiotic response. Moreover, generations of multiple gene knockout mouse models further allow us to identify unique and redundant pathways mediated by each xenosensor. In this article, we review the progress made by using animal models of RXRs, PXR, and CAR in understanding the biological functions of these nuclear receptors in physiology, pharmacology, and pathology.

Animals↗

Sympathoinhibitory function of the alpha(2A)-adrenergic receptor subtype.

Presynaptic alpha(2)-adrenergic receptors (alpha(2)-AR) are distributed throughout the central nervous system and are highly concentrated in the brain stem, where they contribute to neural baroreflex control of blood pressure (BP). To explore the role of the alpha(2A)-AR subtype in this function, we compared BP and plasma norepinephrine and epinephrine levels in genetically engineered mice with deleted alpha(2A)-AR gene to their wild-type controls. At baseline, the alpha(2A)-AR gene knockouts (n=11) versus controls (n=10) had higher systolic BP (123+/-2.5 versus 115+/-2.5 mm Hg, P<0. 05), heart rate (730+/-15 versus 600+/-18 b/min, P<0.001), and norepinephrine (1.005+/-0.078 versus 0.587+/-0.095 ng/mL, P<0.01), respectively. When submitted to subtotal nephrectomy and given 1% saline as drinking water, both alpha(2A)-AR gene knockouts (n=14) and controls (n=14) became hypertensive, but the former required 15. 6+/-2.5 days versus 29.3+/-1.4 days for the controls (P<0.001). End-point systolic BP was similar for both at 155+/-2.1 versus 152+/-5.2 mm Hg, but norepinephrine and epinephrine levels were twice as high in the knockouts at 1.386+/-0.283 and 0.577+/-0.143 versus 0.712+/-0.110 and 0.255+/-0.032 ng/mL, respectively, P<0.05 for both. We conclude that the alpha(2A)-AR subtype exerts a sympathoinhibitory effect, and its loss leads to a hypertensive, hyperadrenergic state.

Animals↗

The mousetrap: what we can learn when the mouse model does not mimic the human disease.

In recent years, mouse models for human metabolic diseases have become commonplace because the information gained from in vivo study of biochemical pathways is invaluable, and many metabolic diseases are relatively easy to recreate in mice through gene knockout technology in embryonic stem cells. In certain cases, however, the knockout mice may reproduce only some of the human disease phenotype, may be more severely affected than human cases, or may have no clinical phenotype at all. Under these circumstances, the disease pathology can become more complex, causing the researcher to evaluate basic differences in mouse and human biology as well as questions of genetic background, alternate pathways, and possible gene interactions. This review is a brief analysis of gene knockout models for Lesch-Nyhan syndrome, Lowe syndrome, X-linked adrenoleukodystrophy, Fabry disease, galactosemia, glycogen storage disease type II, metachromatic leukodystrophy, and Tay-Sachs disease, which produce a biochemical model of disease but often do not reproduce clinical symptoms. These mice may be useful for studying the biochemical and physiological pathways in which certain metabolites function toward embryonic and fetal development, as well as specific functions in various organs, and they may provide an inexpensive and useful model system for development of new therapeutic techniques.

Animals↗

Rapid action of 17beta-estradiol on kainate-induced currents in hippocampal neurons lacking intracellular estrogen receptors.

17Beta-estradiol can potentiate kainate-induced currents in isolated hippocampal CA1 neurons. The action of estrogen was rapid in onset, steroid and stereospecific, and reversible. The potentiation could be mimicked by 8-bromo-cAMP, an activator of protein kinase A. As the hippocampus expresses both isoforms of the intracellular estrogen receptor (ER alpha and ER beta), the role of ERs in the rapid action of 17beta-estradiol remains elusive. Here we report that the rapid action of 17beta-estradiol is independent from the classical ER activation in the modulation of membrane excitability. Under whole cell voltage clamp recording configuration, 17beta-estradiol-induced potentiation was observed in both wild-type and the ER alpha gene knockout mice. The perfusion or incubation of ICI 182,780, which blocks both ER alpha and ER beta, did not affect estrogen potentiation in either group. Further study showed that adenosine 3',5'-cyclic-monophosphothioate Rp-isomer, a specific inhibitor of protein kinase A, completely blocked the potentiation observed with the application of 17beta-estradiol in ER alpha gene knockout mice. Our results provide evidence that a distinct estrogen-binding site exists, which appears to be coupled to alpha-amino-3-hydroxyl-5-methyl-4-isoxazole proprionic acid/kainate receptors by a cAMP-dependent phosphorylation process.

Animals↗

Haptoglobin and malaria.

Haptoglobin gene knockout mice and wild-type controls were infected with Plasmodium berghei ANKA or Plasmodium chabaudi. The peak parasitaemia and parasite burden were higher in Hp-/- mice than in Hp+/+ mice. The increase in spleen weight following malaria infection was smaller in Hp-/- mice than in Hp+/+ animals. The occurrence of cerebral malaria in P. berghei ANKA infection was not different in Hp gene knockout mice and their controls.

Animals↗

Dose-related opposite modulation by nociceptin/orphanin FQ of substance P nociception in the nociceptors and spinal cord.

We previously reported that the intraplantar (i.pl.) application of nociceptin/orphanin FQ (N/OFQ) at extremely low doses elicited a nociception through a substance P (SP) release from nociceptor endings. In the present study, the nociception induced by SP (and N/OFQ) was abolished by intrathecal (i.t.) injection of neurokinin(1) (SP receptor) antagonist, suggesting the involvement of the stimulation of nociceptive primary SP neuron and SP release into spinal synapses. On the other hand, similar low doses of N/OFQ (i.t.) exerted nociceptive responses, characterized by scratching, biting, and licking, and these responses were blocked by an neurokinin(1) antagonist (i.t.) or capsaicin pretreatment or in tachykinin 1 gene knockout mice (tac1(-/-) mice), suggesting that N/OFQ receptor (NOR) also exists on the spinal terminals of SP neurons. When wide ranges of N/OFQ doses were used, a typical bell-shaped dose-response relationship was observed in both peripheral and central nociception tests. Furthermore, N/OFQ (1 nmol) administered i.pl. blocked SP (i.pl.)-induced flexor responses, which were abolished by pertussis toxin pretreatment or in NOR gene knockout (NOR(-/-)) mice. On the other hand, N/OFQ administered i.t. blocked SP (i.t.)-induced scratching, biting, and licking in capsaicin-pretreated and tac1(-/-) mice, and this antinociception was abolished in NOR(-/-) mice. All these findings suggest that N/OFQ has biphasic actions depending on doses in the nociceptors and spinal synapses and has postsynaptic antinociceptive actions in spinal cord by modulating SP signaling.

Analgesics↗

Beta7 integrins contribute to skin graft rejection.

BACKGROUND: Because integrins alpha4beta7 and alphaEbeta7 contribute to epidermotropism of T-cells during skin inflammation, we sought to study their role in skin allograft rejection. METHODS: Wild-type (WT) (beta7+/+) and beta7 gene knockout (beta7-/-) C57BL/6 (H-2(b)) mice and SJL/J (H-2(s)) mice served as donors and recipients of allogeneic skin grafts. An anti-integrin beta7 subunit mAb (FIB504.64) was used to treat WT beta7+/+ C57BL/6 recipients of skin grafts from SJL/J mice. RESULTS: WT C57BL/6 recipients acutely rejected skin from SJL/J mice in 13 days. In contrast, the survival of SJL/J skin on either beta7-/- gene knockout or WT C57BL/6 recipients treated with anti-beta7 subunit mAb, was prolonged by 6 to 7 additional days (P<0.01). The survival of skin allografts from either beta7-/- or beta7+/+ C57BL/6 mice received by SJL/J recipients was not prolonged (P >0.05). CONCLUSIONS: Beta7 integrins contribute to skin graft rejection, in accord with their role in mediating the epidermotropism of T-cells during skin inflammation.

Animals↗

Ah receptor-dependent CYP1A induction by two carotenoids, canthaxanthin and beta-apo-8'-carotenal, with no affinity for the TCDD binding site.

The assays of several phase I and phase II xenobiotic-metabolizing enzyme activities, as well as CYP1A immunoblot analysis, were performed in liver microsomes and cytosol of male C57BL/6 mice (Ah receptor-responsive), of male DBA/2 mice (Ah receptor-low responsive) and of female Ah receptor gene knockout mice that were fed diets containing 300 mg/kg of a nonprovitamin A carotenoid, canthaxanthin, or a provitamin A carotenoid, beta-apo-8'-carotenal for 14 days, or which were injected i.p. with 3-methylcholanthrene. Previous studies have shown that some carotenoids, such as canthaxanthin and beta-apo-8'-carotenal, are strong inducers of liver CYP1A1 and 1A2 when given to rats. In this work, only canthaxanthin induced both CYP1A1 and 1A2 in C57BL/6 mice, whereas beta-apo-8'-carotenal induced only CYP1A2 in this strain. Neither of the two carotenoids modified CYP1A1/2 protein contents or enzyme activities in Ah receptor-low responsive DBA/2 or in Ah receptor gene knockout mice. Cytosol prepared from C57BL/6 mice liver tissue was incubated with [3H] 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the presence of canthaxanthin or beta-apo-8'-carotenal and analyzed by sucrose density gradient sedimentation: neither of the carotenoids, even when present in large excess, competed with TCDD for the TCDD binding site of the cytosolic Ah receptor of C57BL/6 mice. In brief, the carotenoids canthaxanthin or beta-apo-8'-carotenal induced Cyp1a genes in mice through an Ah receptor-dependent pathway, but did not bind to the Ah receptor.

Animals↗

Catalytic RAG1 mutants obstruct V(D)J recombination in vitro and in vivo.

To generate severe combined immunodeficient (SCID) livestocks for xenotransplantation, we have attempted to generate a SCID phenotype without gene knockout. Based on the reported mouse RAG1 mutants, we constructed the corresponding rabbit RAG1 mutants by mutagenesis of three residues within the catalytic domain: D602A, D710A, and E964A. As expected, these mutants each exhibited no catalytic activity on artificial substrates and inhibited recombination by the wild type RAG1. Moreover, replacement of the N-terminus of RAG1 with enhanced green fluorescent protein (EGFP) greatly increased protein stability, and the triple mutant RAG1 showed a twofold increase in its ability to inhibit wild type activity in vitro. We generated mice transgenic for the latter mutant to assess its effect on V(D)J recombination in vivo. Serum IgM levels in four out of seven transgenic mice were reduced to approximately 30-50% of control levels in four out of seven transgenic mice. Our results suggest that immunodeficient animals for regenerative medicine could be generated without gene knockout.

3T3 Cells↗

Phagocyte-derived reactive oxygen species do not influence the progression of murine blood-stage malaria infections.

Phagocyte-derived reactive oxygen species have been implicated in the clearance of malaria infections. We investigated the progression of five different strains of murine malaria in gp91(phox-/-) mice, which lack a functional NADPH oxidase and thus the ability to produce phagocyte-derived reactive oxygen species. We found that the absence of functional NADPH oxidase in the gene knockout mice had no effect on the parasitemia or total parasite burden in mice infected with either resolving (Plasmodium yoelii and Plasmodium chabaudi K562) or fatal (Plasmodium berghei ANKA, Plasmodium berghei K173 and Plasmodium vinckei vinckei) strains of malaria. This lack of effect was apparent in both primary and secondary infections with P. yoelii and P. chabaudi. There was also no difference in the presentation of clinical or pathological signs between the gp91(phox-/-) or wild-type strains of mice infected with malaria. Progression of P. berghei ANKA and P. berghei K173 infections was unchanged in glutathione peroxidase-1 gene knockout mice compared to their wild-type counterparts. The rates of parasitemia progression in gp91(phox-/-) mice and wild-type mice were not significantly different when they were treated with l-N(G)-methylarginine, an inhibitor of nitric oxide synthase. These results suggest that phagocyte-derived reactive oxygen species are not crucial for the clearance of malaria parasites, at least in murine models.

Animals↗

Morphologic and functional characterization of perforin-deficient lymphokine-activated killer cells.

Mice deficient in perforin, a key mediator of lymphocyte-mediated cytolysis, have recently been generated using the gene knockout technique. CTL and NK cells derived from these mice have been shown to be defective in the granule-dependent cytolytic pathway. To investigate whether the granule-formation process has been altered in these perforin-deficient cytotoxic cells, rendering them defective in using the other granule mediators, we have examined in the present study the morphologic and functional characteristics of perforin-deficient LAK cells. Perforin-deficient LAK cells, similar to wild-type LAK cells, were shown to contain a large number of granules in their cytoplasm. By electron microscopy, the morphology of the granules present in these two cell populations appeared indistinguishable. The complete depletion of perforin in LAK cells derived from perforin gene-knockout mice was further confirmed by immunoelectron microscopy using anti-perforin antiserum. The expression of other cytolytic mediators, present either within the granules (granzymes A and B) or elsewhere (Fas ligand), appeared to be unperturbed, as investigated using the reverse transcription-PCR technique. Like the CTL and NK cells isolated from perforin-deficient mice, perforin-deficient LAK cells could lyse only target cells that express high levels of Fas molecule. Furthermore, these perforin-deficient LAK cells, similar to wild-type LAK cells and a CTL clone, were resistant to perforin-mediated cytolysis.

Animals↗

Mechanisms of immunity to Ehrlichia muris: a model of monocytotropic ehrlichiosis.

Ehrlichia species can cause life-threatening infections or chronic persistent infections. Mechanisms of protective immunity were examined in an Ehrlichia muris mouse model of monocytotropic ehrlichiosis. C57BL/6 mice possessed strong genetic resistance to E. muris of an undetermined mechanism. CD8 T lymphocytes were particularly important, as revealed by 81% fatalities for E. muris-infected, major histocompatibility complex class I gene knockout mice compared with no deaths for wild-type C3H mice. Moreover, 80% of C3H mice depleted of CD8 and CD4 cells died of E. muris infection compared with only 44% of CD4 cell-depleted mice. CD8 T lymphocytes were demonstrated for the first time in an Ehrlichia infection to exhibit cytotoxic T-lymphocyte activity against Ehrlichia-infected target cells. Both gamma interferon and tumor necrosis factor were shown to play synergistic roles in protective immunity in vivo for the first time, as demonstrated by 75% fatalities when both cytokines were neutralized compared with minimal mortality when they were depleted separately. Passive transfer of antibodies, but not Fab fragments, to E. muris protected C3H/SCID mice against lethal infection. The mechanism of increased susceptibility (22% lethality) of C57BL/6 major histocompatibility complex class II gene knockout mice and CD4 cell-depleted C3H mice (i.e., through a gamma interferon or antibody mechanism), as well as the more important role of CD8 T lymphocytes (in the form of cytotoxic T-lymphocyte activity and/or gamma interferon production), remains to be elucidated. Protective immunity against monocytotropic E. muris is mediated by a combination of CD8 and CD4 T lymphocytes, gamma interferon, tumor necrosis factor alpha, and antibodies.

Animals↗

CD8+ T cell effector mechanisms in resistance to infection.

Based on T cell subset depletion studies and the analysis of gene knockout mice, it is evident that CD8(+) T cells contribute to resistance against intracellular infections with certain viral, protozoan, and bacterial pathogens. Although they are known primarily for their capacity to kill infected cells, CD8(+) T cells elaborate a variety of effector mechanisms with the potential to defend against infection. Microbes use multiple strategies to cause infection, and the nature of the pathogenhost interaction may determine which CD8(+) T cell effector mechanisms are required for immunity. In this review, we summarize our current understanding of the effector functions used by CD8(+) T cells in resistance to pathogens. Analyses of mice deficient in perforin and/or Fas demonstrate that cytolysis is critical for immunity against some, but not all, infections and also reveal the contribution of cytolysis to the pathogenesis of disease. The role of CD8(+) T cell-derived cytokines in resistance to infection has been analyzed by systemic treatment with neutralizing antibodies and cytokine gene knockout mice. These studies are complicated by the fact that few, if any, cytokines are uniquely produced by CD8(+) T cells. Thus, the requirement for CD8(+) T cell- derived cytokines in resistance against most pathogens remains to be defined. Finally, recent studies of human CD8(+) T cells reveal the potential for novel effector mechanisms in resistance to infection.

Animals↗

nanos1: a mouse nanos gene expressed in the central nervous system is dispensable for normal development.

A mouse nanos (nanos1) gene was cloned and its function was examined by generating a gene-knockout mouse. The nanos1 gene encodes an RNA-binding protein, which contains a putative zinc-finger motif that exhibits similarity with other nanos-class genes in vertebrates and invertebrates. Although nanos1 is not detected in primordial germ cells, it is observed in seminiferous tubules of mature testis. Interestingly, maternally expressed nanos1 is observed in substantial amounts in oocytes, but the amount of maternal RNA is rapidly reduced after fertilization, and the transient zygotic nanos1 expression is observed in eight-cell embryos. At 12.5 days postcoitum, nanos1 is re-expressed in the central nervous system and the expression continues in the adult brain, in which the hippocampal formation is the predominant region. The nanos1 -deficient mice develop to term without any detectable abnormality and they are fertile. No significant neural defect is observed in terms of their behavior to date.

Amino Acid Sequence↗

Bax, caspase-2, and caspase-3 are required for ovarian follicle loss caused by 4-vinylcyclohexene diepoxide exposure of female mice in vivo.

The industrial chemical, 4-vinylcyclohexene diepoxide (VCD), kills oocytes within immature follicles in the ovaries of mice and rats and is considered a potential occupational health hazard. It has been reported that VCD-induced follicle loss occurs via a cell death process involving elevated expression of Bax, a proapoptotic Bcl-2 family member, and increased caspase-3-like activity. We have previously shown that oocytes lacking acid sphingomyelinase (ASMase; an enzyme that generates the proapoptotic stress sensor ceramide), the aromatic hydrocarbon receptor (Ahr), Bax, or caspase-2 are resistant to apoptosis induced by other chemical toxicants. Therefore, this study was designed to investigate the functional importance of ASMase, Ahr, Bax, and caspase-2 as well as the related executioner enzyme caspase-3 to VCD-induced ovotoxicity in mice using gene knockout technology. For each gene mutant mouse line, wild-type and homozygous-null female siblings derived from heterozygous matings were given once-daily ip injections of either vehicle (sesame oil) or VCD (80 mg/kg body weight) for 15 d (three or four mice per treatment group per genotype). Ovaries were collected 24 h after the final injection and analyzed for the total number of nonatretic primordial and primary follicles remaining per ovary. No differences in the extent of primordial or primary follicle destruction resulting from VCD exposure were observed in wild-type vs. ASMase- or Ahr-deficient mice. By contrast, the extent of VCD-induced primordial follicle depletion in Bax-deficient mice (45 +/- 11%) was significantly (P < 0.05) lower than that in wild-type females (85 +/- 2%). The extent of primary follicle loss in bax-null mice exposed to VCD (3 +/- 22%) was also significantly (P < 0.05) lower than that in their wild-type sisters (86 +/- 4%). In caspase-2-deficient mice, significantly (P < 0.05) fewer oocyte-containing primary follicles were destroyed by VCD (17 +/- 19%) vs. wild-type controls (71 +/- 6%); however, no significant difference in the extent of VCD-induced primordial follicle destruction was observed in caspase-2-null vs. wild-type females. Finally, in caspase-3-deficient mice, significantly (P < 0.05) fewer oocyte-containing primary follicles were destroyed by VCD (33 +/- 3%) vs. wild-type controls (71 +/- 2%); however, no significant difference in the extent of VCD-induced primordial follicle destruction was observed in caspase-3-null vs. wild-type females. We conclude that Bax, caspase-2, and caspase-3, but not ASMase or Ahr, are functionally important in VCD-induced follicle loss. However, as a loss of Bax, caspase-2, or caspase-3 function conveyed only partial protection from the ovotoxic effects of VCD, other cell death pathways that either function independently of Bax, caspase-2, and caspase-3 or are not apoptotic in nature are also involved.

Animals↗

A novel biocontrol Pseudomonas species with broad-spectrum antagonistic activity against phytopathogens.

Bacterial and fungal diseases cause significant losses in horticultural crops, and biocontrol using beneficial microorganisms offers a sustainable alternative to chemical pesticides. In this study, a novel Pseudomonas strain D3 was isolated from Actinidiae rhizosphere. D3 exhibited strong antibacterial activity in LB medium but showed no activity against fungi or oomycetes. However, when cultured in KIDO medium, it demonstrated potent antifungal activity. Phylogenetic analysis based on 16S rRNA gene showed that D3 was most closely related to Pseudomonas mosselii CIP_105259T, while whole-genome sequencing revealed ANI values below 95% with eight known P. mosselii strains. Digital DNA-DNA hybridization (dDDH) further confirmed its genomic distinctiveness, with the highest dDDH value (58.2%) against the type strain P. mosselii DSM 17497T, well below the 70% species delineation threshold, supporting D3 as a novel Pseudomonas species. Functional validation via targeted gene knockout revealed a dichotomy in the antagonistic mechanisms of D3. Knockout of individual biosynthetic gene clusters (BGCs) only partially reduced antibacterial activity against Pseudomonas syringae pv. actinidiae, indicating that multiple BGCs contribute to this activity in a partially redundant manner. In contrast, disruption of a specific lipopeptide synthase cluster completely abolished antifungal activity against Valsa mali. LC-MS/MS analysis confirmed that this lipopeptide was produced exclusively in KIDO medium, consistent with the observed medium-dependent antifungal activity. Detached leaf and twig assays showed that D3 provides strong preventive biocontrol against both pathogens. Collectively, strain D3 employs a dual biocontrol mechanism, combining antibacterial activity mediated by multiple BGCs with lipopeptide-dependent antifungal activity, positioning it as a promising agent for sustainable disease management in horticultural crops.

Pseudomonas↗