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Control of expression and methylation of a hepatitis B virus transgene by strain-specific modifiers.

In transgenic animals, genotype-specific modifiers exert a control over transgene methylation and expression that may or may not be position dependent. These factors belong to different classes, some of them possibly related to modifiers of position-effect variegation in Drosophila. The study of hepatitis B virus (HBV) gene expression in transgenic mice has revealed the existence of many factors influencing transcription, including hormones and tissue-specific transcription factors. We now report the effect of genotype-specific modifiers on HBV surface antigen (HBsAg) expression and transgene methylation. Compared with the C57BL/6 background, the DBA/2 and 129sv backgrounds cause enhancement of HBsAg expression, with little or not effect on transgene methylation or transcription. In contrast, a single cross with a BALB/c mouse is responsible for de novo methylation and silencing of the transgene in all offspring. Several modifiers appear to segregate in the progeny of a transgenic E36 male mouse crossed with (C57BL/6 x BALB/c) F1 females, with the emergence of a high-expressor group. Our observations suggest that different modifiers act cooperatively, at both the transcriptional and post-transcriptional levels, as part of a complex system regulating transgene expression. This transgenic model provides a system to genetically map new mouse strain-specific modifiers, some of them involved in epigenetic modification and transcription control.

Animals↗

Use of cloned genetically modified human fibroblasts to assess long-term survival in vivo.

Because human fibroblasts are easily brought to tissue culture conditions and can be stably transduced with retroviral vectors encoding transgenes ex vivo, genetically modified fibroblasts are frequently considered in strategies to correct disease with gene therapy. This enthusiasm has been dampened by studies showing that transgene expression by genetically modified fibroblasts diminishes with time in vivo, but not in vitro, for reasons that are unclear. We elected to study this problem using cloned human fibroblasts that had been cloned by limiting dilution and stably transduced with a retroviral vector encoding lacZ ex vivo. These were seeded onto a nonbiodegradable nylon matrix that was transplanted to nude mice. Transgene expression was followed prospectively by histologic exam. Data show that human fibroblasts can withstand the pressure of cloning by limiting dilution. In addition, they can be passaged from 10 to > 20 times, and > 1 x 10(20) of genetically modified fibroblasts can be generated as progeny of one cell. Loss of transgene expression by the cloned genetically modified fibroblasts in vivo occurs in an orderly and progressive fashion, but is not complete by 4 months. Neither the loss nor the persistence of expression appear to be random. These observations are most compatible with the thesis that a major cause of the loss of transgene expression in vivo is secondary to apoptosis of the genetically modified fibroblast. Loss of expression of transgenes in senescent genetically modified fibroblasts occurs more rapidly than in their presenescent counterparts in the age-neutral, in vivo setting of the nude mouse.

Animals↗

Characterization of the DNA damage recognized by an antiserum elicited against cis-diamminedichloroplatinum (II)-modified DNA.

A series of in vitro and in vivo studies were performed to characterize DNA damage recognized by an antiserum elicited against DNA modified with cis-diamminedichloroplatinum(II) (cisplatin). Adducts determined by the cisplatin-DNA enzyme-linked immunosorbent assay (ELISA) in human blood cell DNA have been shown to correlate well with positive clinical outcome in testicular and ovarian cancer patients receiving platinum drug-based chemotherapy (Reed et al. (1990) Proc. Natl. Acad. Sci., 84; 5024, and Reed et al. (1988) Carcinogenesis, 9, 1909). DNAs from calf thymus, salmon sperm, pBR322 and synthetic oligonucleotides were modified with cisplatin in vitro before or after specific DNA digestion steps to yield adducted samples of known size and/or chemical composition. These cisplatin modified DNAs were assayed by atomic absorption spectrometry (AAS) to assess absolute platinum content, and by ELISA to determine the antiserum specificity. The antiserum recognizes native cisplatin-modified calf thymus DNA, and native oligonucleotides containing intrastrand cis-Pt (NH3)2-d(pGpG) adducts (Pt-GG) and intrastrand cis-Pt (NH3)2-d(pApG) adducts (Pt-AG). Modified plasmid DNA fragments of varying sizes (down to 309 base pairs) are recognized similarly to cisplatin-modified calf thymus DNA. The antiserum does not cross-react with individual Pt-GG or Pt-AG adducts not bound to DNA. In experiments designed to assess the relationship between adduct measured by ELISA and total platinum bound to DNA as measured by AAS, male and female Sprague-Dawley rats were injected i.p. with cisplatin and a dose response for adduct formation was determined in kidney DNA samples. Values obtained by ELISA were substantially lower than those measured by AAS, and the two were directly related in DNA from kidney tissues of rodents but not in DNA from human nucleated blood cells. In rodent samples the ELISA measured a consistent 0.2% of the total DNA-bound platinum determined by AAS, with a correlation coefficient of 0.91. Among 54 blood cell DNA samples from human patients, which gave measurable adduct values in both ELISA and AAS, the ELISA measured a variable fraction (0.2-33.0%) of the total DNA-bound platinum measured by AAS. We conclude that the cisplatin-DNA ELISA measures a three dimensional lesion in DNA that is formed in direct proportion to total DNA-bound platinum in rat kidney, but that in human biological samples, interindividual variability precludes a relationship that conforms to simple mathematical algorithms.

Animals↗

Translation of satellite tobacco necrosis virus RNA modified by (not equal to)-r-7,t-8-dihydroxy-t-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene is inhibited in a wheat germ cell-free system.

It has been shown that (not equal to)-r-7-,t-8-dihydroxy-t-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE) modification of rabbit globin mRNA results in inhibition of translational initiation. In order to explore the possibility that modification of the 5' cap structure was responsible for this inhibition, the naturally non-capped mRNA from satellite tobacco necrosis virus (STNV) was reacted with BPDE and translated in a wheat germ cell-free system. The extent of modification was 1.3 and 2.9 BPDE residues/molecule. High performance liquid chromatography of the modified nucleosides from enzymatically hydrolyzed STNV RNA revealed that greater than 90% of the nucleoside adducts were substituted at the exocyclic amino group of guanosine. The translational ability of the lower and higher modified STNV, measured by incorporation of [14C]amino acids into acid-precipitable polypeptides is inhibited by 55% and 63%, respectively. Polyacrylamide gel electrophoretic analyses of the translation products indicate that predominantly full-length coat proteins are synthesized but with the carcinogen-modified STNV the amount is reduced. On the other hand, 80S initiation complex formation is not inhibited as measured by binding of the BPDE-modified STNV to ribosomes and followed by glycerol gradient centrifugation. Under these conditions, aurintricarboxylic acid completely inhibits 80S initiation complex formation in the presence of either modified or native STNV. These results suggest that inhibition of in vitro translation of BPDE-modified STNV, in contrast to that of globin mRNA, is not at the level of initiation complex formation but possibly by premature termination of growing polypeptides.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗

Monoclonal antibodies to a benzo[a]pyrene diolepoxide modified protein.

Monoclonal antibodies have been developed which specifically recognize protein modified by 7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE-I). These antibodies have been characterized as to sensitivity and specificity by an enzyme-linked immunosorbent assay. They react with BPDE-I-modified proteins and do not cross-react with non-modified protein. All the antibodies have higher sensitivity toward BPDE-I-tetraols than to BPDE-I-modified protein. They cross-react with BPDE-I-deoxyguanosine, BPDE-I-DNA and BPDE-II-rabbit serum albumin. Because of the high antibody sensitivity for tetraols, an immunoassay was developed for quantitating DNA and protein adducts based on release of tetraols from modified samples. This approach was validated using radiolabeled BPDE-I modified DNA and protein.

Antibodies, Monoclonal↗

Weakener of white (Wow), a gene that modifies the expression of the white eye color locus and that suppresses position effect variegation in Drosophila melanogaster.

A locus is described in Drosophila melanogaster that modifies the expression of the white eye color gene. This trans-acting modifier reduces the expression of the white gene in the eye, but elevates the expression in other adult tissues. Because of the eye phenotype in which the expression of white is lessened but not eliminated, the newly described locus is called the Weakener of white (Wow). Northern analysis reveals that Wow can exert an inverse or direct modifying effect depending upon the developmental stage. Two related genes, brown and scarlet, that are coordinately expressed with white, are also affected by Wow. In addition, Wow modulates the steady state RNA level of the retrotransposon, copia. When tested with a white promoter-Alcohol dehydrogenase reporter. Wow confers the modifying effect to the reporter, suggesting a requirement of the white regulatory sequences for mediating the response. In addition to being a dosage sensitive regulator of white, brown, scarlet and copia, Wow acts as a suppressor of position effect variegation. There are many dosage sensitive suppressors of position effect variegation and many dosage-sensitive modifiers of gene expression. The Wow mutations provide evidence for an overlap between the two types of modifiers.

ATP-Binding Cassette Transporters↗

Mutation-selection balance at a modifier-of-imprinting locus.

We propose a pair of population genetic models for a modifier-of-imprinting locus for which different genotypes imprint different proportions of an imprintable target locus in their gametes. The two models examine the situations in which imprinting is advantageous, and we discuss three cases for which the modifier is respectively partially dominant, dominant, or recessive. The models predict the stable equilibrium frequencies of the mutant modifier and functionally diploid individuals in a large population in terms of up to four parameters: the mutation rate at the modifier locus, nu; the selection coefficient against the disadvantageous phenotype, sigma; the proportion of unimprinted eggs produced by homozygotes for the mutant modifier, theta, and, in the partially dominant models, the dominance parameter, kappa. The equilibrium frequency of the mutant phenotypes is shown to be approximately twice that of standard Mendelian models: 2 nu/sigma or 4nu/sigma when the modifier is recessive or dominant, respectively. Mathematical equivalences between these and nonimprinting models are noted.

Chromosome Mapping↗

Efficacy of modified human immune serum globulin in the treatment of experimental murine infections with seven immunotypes of Pseudomonas aeruginosa.

Modified immune serum globulin, prepared from human immune serum globulin by a nonenzymatic method, is apparently safe for intravenous administration to humans. The efficacy of the preparation was determined in experimental murine infections with seven immunotypes of Pseudomonas aeruginosa. Intravenously administered 0.85 percent NaCl, 0.3 m glycine, and 10 percent human albumin did not protect against lethal pseudomonas infection, whereas modified immune serum globulin given by the same route did protect mice. In the mouse protection test, the mean dose of the preparation that saved 50 percent of mice infected with any of eight strains of P. aeruginosa was 480 mg/kg (range, 12-2,333 mg/kg). For five strains the 50 percent effective dose was smaller than 200 mg/kg. There was no correlation between the efficacy of modified immune serum globulin in the mouse protection test and titers of antibody, as determined by bacterial agglutination. Therapy of pseudomonas infection in mice with modified immune serum globulin was followed by a prompt and persistent decrease in the numbers of intraperitoneal bacteria. This finding is consistent with the interpretation that modified immune serum globulin acts primarily as an opsonin and not as an antitoxin. Modified immune serum globulin may prove to be useful in the treatment of human infections.

Agglutination Tests↗

Enhancing the catalytic repertoire of nucleic acids. II. Simultaneous incorporation of amino and imidazolyl functionalities by two modified triphosphates during PCR.

The incorporation of potentially catalytic groups into DNA is of interest for the in vitro selection of novel deoxyribozymes. We have devised synthetic routes to a series of three C7 modified 7-deaza-dATP derivatives with pendant aminopropyl, Z-aminopropenyl and aminopropynyl side chains. These modified triphosphates have been tested as substrates for Taq polymerase during PCR. All the modifications are tolerated by this enzyme, with the aminopropynyl side chain giving the best result. Most protein enzymes have more than one type of catalytic group located in their active site. By using C5-imidazolyl-modified dUTPs together with 3-(aminopropynyl)-7-deaza-dATP in place of the natural nucleotides dTTP and dATP, we have demonstrated the simultaneous incorporation of both amino and imidazolyl moieties into a DNA molecule during PCR. The PCR product containing the four natural bases was fully digested by XbaI, while PCR products containing the modified 7-deaza-dATP analogues were not cleaved. Direct evidence for the simultaneous incorporation during PCR of an imidazole-modified dUTP and an amino-modified 7-deaza-dATP has been obtained using mass spectrometry.

Binding Sites↗

Z-DNA conformation of N-2-acetylaminofluorene modified poly(dG-dC).poly(dG-dC) determined by reactivity with anti cytidine antibodies and minimized potential energy calculations.

The conformation of poly(dG-dC).poly(dG-dC), poly(dG).poly(dC), and calf thymus DNA modified with N-acetoxy-N-2-acetylaminofluorene (N-acetoxy-AAF) was examined by extent of reaction with anti cytidine antibodies. In contrast to modified poly(dG).poly(dC0 and DNA, modified poly(dG-dC).poly (dG-dC) failed to react with the antibodies indicating that the base pairing in this polymer is intact. This in consistent with induction of the Z-DNA conformation in AAF modified poly(dG-dC).poly(dG-dC). Using minimized potential energy calculations on the dCpdG-AAF dimer as a model for the modified polymer, it is shown that the proposed Z-DNA conformation is energetically stable. A model is proposed for an AAF modified tetramer, dGpdCpdGpdC, in which the AAF is external to the Z-DNA duplex.

2-Acetylaminofluorene↗

Modified DNA aptamers against sweet agent aspartame.

We obtained a modified DNA aptamer against sweetener, aspartame, by in vitro selection method. The modified DNA was prepared from dATP, dGTP, dCTP and a modified dTTP bearing a terminal amino group at C-5 position in place of thymidine by PCR using a hyper thermophilic DNA polymerase, KOD Dash DNA polymerase. The synthetic 102-mer DNA with a 60-mer random region was used as an initial template for the PCR. The PCR-amplified modified DNA library was applied to an aspartame-agarose column, and then the bound modified DNA was eluted from the column for the affinity chromatography selection. Repeating the procedure, we selected the modified DNA aptamer against aspartame.

Aspartame↗

Glycolaldehyde-modified low density lipoprotein leads macrophages to foam cells via the macrophage scavenger receptor.

It was shown that proteins modified with advanced glycation end products (AGE) are effectively endocytosed by macrophages or macrophage-derived cells in vitro, and immunohistochemical studies involving anti-AGE antibodies demonstrated the accumulation of AGE-modified proteins (AGE-proteins) in macrophage-derived foam cells in human atherosclerotic lesions in situ, suggesting the involvement of AGE-modified LDL in the atherogenic process in vivo. To examine this suggestion, LDL was modified with glycolaldehyde, a highly reactive intermediate of the Maillard reaction. Physicochemically, glycolaldehyde-modified LDL (GA-LDL) was characterized by increases in negative charge, fluorescence intensity, and reactivity to anti-AGE antibodies, properties highly similar to those of AGE-proteins. The cellular interaction of GA-LDL with mouse peritoneal macrophages showed that GA-LDL was specifically recognized and endocytosed, followed by lysosomal degradation. The endocytic uptake of GA-LDL by these cells was competitively inhibited by acetylated LDL (acetyl-LDL), and the endocytic degradation of acetyl-LDL was also competed for by GA-LDL. Furthermore, incubation of GA-LDL with these macrophages and Chinese hamster ovary cells overexpressing the macrophage scavenger receptor (MSR), but not with peritoneal macrophages from MSR-knockout mice, led to the intracellular accumulation of cholesteryl esters (CE). These results raised the possibility that AGE-modified LDL, if available in situ, is taken up by macrophages mainly via MSR and then contributes to foam cell formation in early atherosclerotic lesions.

Acetaldehyde↗

Characterization of phospholipase A activity of beta1-bungarotoxin from Bungarus multicinctus venom. II. Identification of the histidine residue of beta1-bungarotoxin modified by p-bromophenacyl bromide.

beta1-Bungarotoxin modified with p-bromophenacyl bromide (BPB) was reduced and carboxymethylated, and the resulting two constituent RCM-polypeptide chains (the RCM-A and B chains) were separated. The RCM-A chain was found to be modified by BPB by measuring its UV absorption spectrum and was shown to have lost one histidine residue by analyzing its amino acid composition. To determine the location of the modified histidine residue in the A chain of the toxin, the RCM-A chain was digested with TPCK-trypsin, and the resulting peptides were fractionated by gel filtration followed by DEAE-cellulose chromatography. The modified residue was finally identified as histidine-48 in the A chain by Edman degradation and from the amino acid composition of the BPB-modified peptide. The amino acid sequence around the modified histidine residue in the A chain is highly homologous with those of porcine pancreas phospholipase A2 and presynaptic toxin, notexin. We conclude that histidine-48 in the A chain participates in the phospholipase A activity of beta1-bungarotoxin.

Acetophenones↗

Bindings of Ca2+ and substrate analogs to a cobra venom phospholipase A2 in which the alpha-amino group is modified to an alpha-keto group.

The pH dependence of the chemical reaction rate of p-bromophenacyl bromide (BPB) with His 48 of cobra (Naja naja atra) venom phospholipase A2, in which the alpha-NH2 group had been selectively modified to an alpha-keto group, was studied at 25 degrees C and ionic strength 0.1 in the absence of Ca2+. The pH-dependence curve was monophasic with a midpoint at pH 7.9, which corresponds to the pK value of His 48 of the alpha-NH2-modified enzyme, whereas the curve for the intact enzyme was biphasic, indicating participation of two ionizable groups with pK values of 7.3 and 8.55 (Teshima et al. (1982) J. Biochem. 91, 1778-1788). These two groups were thus identified as His 48 and the alpha-NH2 group, respectively. The pH dependence of the binding constant of Ca2+ to the alpha-NH2-modified enzyme was studied at 25 degrees C and ionic strength 0.1 by measuring the tryptophyl fluorescence changes. The pH-dependence curve was very similar to that for the intact enzyme (Teshima et al. (1981) J. Biochem. 89, 13-20), and it was interpreted in terms of participation of His 48 and Asp 49 (pK 5.4). The absence of participation of the alpha-NH2 group in the Ca2+ binding was thus confirmed. Bindings of monodispersed n-dodecylphosphorylcholine (n-C12PC) and micellar n-hexadecylphosphorylcholine (n-C16PC) to the alpha-NH2-modified enzyme were studied at 25 degrees C and ionic strength 0.1 by the aromatic circular dichroism (CD) and tryptophyl fluorescence methods, respectively. The binding constant of the monodispersed substrate was very similar to that for the intact enzyme (Teshima et al. (1981) J. Biochem. 89, 1163-1174). The binding constant of the micellar substrate to the modified enzyme in the presence of Ca2+ was also very similar to that for the intact enzyme-Ca2+ complex (Teshima et al. (1983) J. Biochem. 94, 223-232), and the pH-dependence curve was interpreted in terms of participation of His 48. On the other hand, the binding constant of the micellar substrate to the modified apoenzyme was much smaller than that for the intact apoenzyme. Nevertheless, the pH-dependence curve could be interpreted in terms of participation of His 48 and Asp 49. From these findings, it was concluded that the ionization state of the alpha-NH2 group of cobra venom phospholipase A2 is essentially irrelevant to the bindings of Ca2+ and also of the monodispersed and micellar substrates.

Animals↗

Modified essay question.

This article examines the reliability and validity of the modified essay question. An 18-item modified essay question was developed and pretested on a group of clinical experts. After the pretest, the modified essay question was administered to a group of 25 physical therapy students immediately before their second level orthopedic placement. A reliability index of .39 (coefficient alpha) was calculated for the test. In addition, measures of validity were obtained by correlating the modified essay question scores with multiple-choice question scores and the students' in-clinic reasoning scores. The results suggest that the reliability coefficient found in this study is comparable to the medical literature. Also, the results showed that the modified essay question demonstrated a greater correlation with the in-clinic clinical reasoning score compared with the parallel content multiple-choice examination. Furthermore, preliminary evidence suggests that the modified essay question may be a useful paper and pencil tool in evaluating clinical reasoning. Finally, several shortcomings of this study are discussed in conjunction with a direction for further study.

Adult↗

Modified Blalock-Taussig shunt patency for pulmonary atresia: assessment with electron beam CT.

PURPOSE: The purpose of this work was to evaluate electron beam CT (EBCT) for the noninvasive assessment of modified Blalock-Taussig (BT) shunt patency in patients with pulmonary atresia. METHOD: Five infants and children with pulmonary atresia and modified BT shunts underwent contrast-enhanced EBCT. Modified BT shunts from the subclavian artery to the pulmonary artery were performed to improve the pulmonary blood flow. Electrocardiogram (ECG)-triggered EBCT was obtained with a 100 ms exposure, 3 mm section thickness, and 2 mm table feed after intravenous administration of contrast material. Three-dimensional (3D) or maximum intensity projection (MIP) EBCT images were compared with conventional angiography. The visibility of modified BT shunts was graded and recorded with use of a four-point scale. RESULTS: Satisfactory visualization was achieved in both 3D and MIP EBCT images to evaluate modified BT shunt patency. CONCLUSION: Contrast-enhanced 3D or MIP EBCT imaging with ECG trigger may be used as an effective substitute to evaluate modified BT shunts with low radiation dose exposure.

Blood Vessel Prosthesis Implantation↗

Bone interface of dental implants cytologically influenced by a modified sandblasted surface: a preliminary in vitro study.

To study the influences of a modified sandblasted surface (developed by the authors) on the integrating status of titanium (Ti) dental implants and bone in vitro, a three-dimensional experimental model of implant material-osteoblast culture was used. The interaction of Ti discs and osteoblasts at the interface was followed with phase-contrast microscope examination and was further observed histologically and ultra-structurally after one-month culture. Results showed that there was no significant difference between the modified sandblasted surface group and the smooth surface group in the capacity of osteoblasts migrating and attaching to Ti discs. There was, however, a significant difference in the pattern of attachment. Around the polished surface, the migrating and attaching osteoblasts oriented themselves parallel to it; however, around the modified sandblasted surface, the osteoblasts were migrating and attaching perpendicularly. There was also a major difference in the shapes of cells lining the interface; spindle-shaped on the smooth surface versus round and ovoid with a large cellular body and abundant cytoplasm on the modified sandblasted surface. Moreover, transmission electron microscopy revealed an active secretion of collagen fibrils, a bone-matrix-vesicles-mediated mineralization process, and the formation of osteocytes in the modified sandblasted surface group. Therefore, at this in vitro level, it can be concluded that the modified sandblasting surface treatment of dental implants can facilitate bone healing at their osseous interface and enable the real perpendicularly connecting bone-fiber osseointegration to form instead of the capsule-like osseous adaptation.

Cell Adhesion↗

Antitumor effects of interleukin-2 gene-modified fibroblasts in an orthotopic colon cancer model.

We transduced the interleukin-2 (IL-2) gene into murine fibroblasts BALBCL7 or murine colon cancer CT26 using a retroviral vector. BALBCL7 transduced with IL-2 gene secreted 748 pg/ml of IL-2, whereas IL-2 gene-modified CT26 secreted 1,167 pg/ml of IL-2 (48 h incubation, 1x10(6)/ml). Then, we inoculated gene-modified BALBCL7 and/or CT26 cells into BALB/c female mice, and observed the tumor growth. The tumor growth was inhibited in mice inoculated with parental CT26 plus IL-2 gene-modified BALBCL7, compared with that in mice given parental CT26 alone (P<0.01). Moreover, we investigated the cytotoxic activity of spleen cells derived from mice treated with gene-modified cells, and performed phenotypic analysis of the effector cells. The killer cells derived from mice inoculated with IL-2 gene-modified BALBCL7 plus parental CT26 showed higher cytotoxic activity than those from mice inoculated with CT26 alone. The cytotoxic activity was almost completely blocked by anti-CD8 antibody (Ab), and partially blocked by anti-asialo GM1 Ab. Next, we inoculated CT26 tumor tissue into murine cecum orthotopically, and treated the animals with gene-modified BALBCL7 plus parental CT26. The tumor size in the cecum was significantly decreased, compared with parental CT26 alone (P<0.01).

Animals↗