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Biomedical subjects

Q Guo

Publications and source records attributed to Q Guo.

At least 163 records · Page 9Linked to original sources
PubMed1993

Ets oncogene-related gene Elg functions in Drosophila oogenesis.

Members of the ets gene family encode transcription factors that regulate the expression of a variety of cellular and viral genes including several protooncogenes. We have utilized Drosophila to elucidate the in vivo function of one family member. We show by complementation rescue and sequence analysis that the female sterile mutant tiny eggs (tne) is an allele of the Drosophila Ets-related gene Elg (also called D-elg). The mutation of a highly conserved tyrosine residue in the ETS DNA-binding domain of the Elg gene product demonstrates that normal gene function is required for proper follicle cell migration, chorion formation, and nurse cell-chromosome decondensation during Drosophila oogenesis.

Amino Acid Sequence↗
PubMed1993

[Percutaneous hot water injection therapy (PHoT) for hepatic tumors: a clinical study].

Percutaneous ethanol injection therapy (PEIT) has become widely used in the treatment of HCC. However, the indications for this method are limited by the toxicity of ethanol itself. Against this background, the authors turned their attention to the heat coagulation necrosis effect induced by boiled physiological saline (hot water) and devised percutaneous hot water injection therapy (PHoT) as a new local treatment method. PHoT was performed a total of 41 times in 13 patients (16 nodules) with HCCs measuring < or = 3 cm. Changes in AFP values, CT findings, angiographic findings before and after treatment, and histopathological findings of needle biopsy or resected specimen were investigated. AFP values decreased in all of the seven patients who initially showed high values. On CT, all lesions receiving PHoT became hypodense, with this change thought to indicate necrosis. Disappearance of the tumor stain was confirmed in the four patients in whom follow-up angiography was performed. In the six patients in whom needle biopsy was performed, disappearance and scaring of tumor cells were observed, while in the one patient in whom the tumor was resected, complete necrosis of the tumor was confirmed. PHoT, despite a small number of punctures, shows good anti-tumor effects, and has promise not only as a curative local treatment method for small HCCs but also in combination with TAE for large HCCs.

Aged↗
PubMed1993

Structure of a parallel-stranded tetramer of the Oxytricha telomeric DNA sequence dT4G4.

We report here the determination of the solution structure of the single-copy tetramer of the sequence dT4G4, the unit repeat in telomeres of the ciliated protozoan Oxytricha, in the presence of potassium ions. This is accomplished by a combination of sequential assignments and distance determinations from 2D proton NMR with model building, based on conformational analysis of the structure using a full-matrix NOESY simulation and molecular dynamics. Each strand in this tetramer structure has an identical environment and conformation: a parallel-stranded, right-handed helix, with all nucleotides in the C2'-endo, anti configuration. The T flanking the G cluster stacks in a 4-fold symmetrical helical array, while the remaining T's become increasingly flexible and sample multiple stacked configurations.

Animals↗
PubMed1993

[CO2US via an implantable port--drug distribution in intraarterial chemotherapy for hepatic tumors and evaluation of effect].

The distribution of blood flow was determined from the distribution of CO2 by US performed during the infusion of CO2 microbubbles via an implantable port (IP-CO2US) in intraarterial chemotherapy for hepatic tumor, and the usefulness of this method in determining tumor vascularity and evaluating the effects of therapy was investigated. A total of 16 patients, 12 of whom had metastatic liver tumor, two hepatocellular carcinoma, one gall bladder carcinoma, and one cholangiocellular carcinoma were studied. The enhanced areas in the liver in 16 patients in whom IP-CO2US was performed a total of 24 times were consistent in all cases with the enhanced areas demonstrated by IP-RI angiography performed a total of 10 times within 10 days, and were also consistent with one exception with the enhanced areas demonstrated by IP-CTA performed 14 times. The tumor detection rate was markedly higher with IP-CO2US than with plain US or IP-DSA, and was similar to that of IP-CTA. Evaluation of the vascularity of individual nodules by IP-CO2US surpassed that by IP-DSA, and was similar to that of IP-CTA. It was demonstrated that blood flow distribution (intrahepatic drug distribution) can be equally well grasped with IP-CO2US, which is a simple and convenient method, as with IP-RI angiography. It was also suggested that IP-CO2US is useful in the evaluation of tumor vascularity and the effect of therapy.

Antineoplastic Agents↗
PubMed1993

Effect of thymine tract length on the structure and stability of model telomeric sequences.

DNA from the telomeres at the ends of eukaryotic chromosomes contains a stretch of simple tandemly repeated sequences in which clusters of G residues alternate with clusters of T/A sequences along one DNA strand. Model telomeric G-clusters form four-stranded structures in Na+ or K+, stabilized by Hoogsteen pairing between G bases. DNA containing a single copy of the G-cluster can self-associate to form tetramers, with a parallel-stranded, right-handed helical structure. Two copies of the 3'-terminal G strand form a folded-back hairpin that dimerizes to create an antiparallel quadruplex structure. We show here that the tetrameric structure is strongly influenced by the T residue flanking either side of the G-cluster. The parallel tetraplex formed by single copies of the sequences dTnG4 is most stable for n = 1 and least stable for n = 8, the longest tract we have studied. At least two thymine residues are required to allow formation of antiparallel folded-back hairpin dimers from two-copy oligomers of sequence d(TnG4)2 in Na+; additional T's destabilize this structure. In K+, the predominant structure formed is the four-stranded parallel tetramer in all cases. Kinetic analysis indicates that the quadruplex structure formed by Oxytricha telomeric DNA overhangs in the presence of Na+ arises by dimerization of two Hoogsteen base-paired hairpins, with a relatively low energy barrier.

Circular Dichroism↗
PubMed1993

[Study on the evaluation of recurrence of HCC and the effect after transcatheter hepatic arterial embolization--fluctuations in AFP values].

To determine the usefulness of alpha-fetoprotein (AFP) in determining recurrence of HCC after interventional angiography (IVA) and to define the relation between AFP and the imaging diagnosis of HCC recurrence, changes in AFP values in 160 patients with hepatocellular carcinoma who were treated by IVA > or = two times were classified into four patterns: A: the AFP value was decreased after the first IVA, increased at recurrence and decreased again after the second IVA; B: the AFP value was unchanged after the first IVA, but increased at recurrence and decreased after the second IVA; C: the AFP value was decreased after the first IVA, but was not increased at recurrence; D: the AFP value showed no change. The frequency of each AFP pattern and the diagnosis of recurrence by AFP were determined. The relation between tumor type and AFP was defined. Pattern A was the most frequently detected. In 62.6%, AFP was increased at recurrence (A and B), and there was a positive correlation between changes in the AFP value and the findings of imaging diagnosis. In another 37.5%, AFP was not increased at recurrence (C and D), and therefore, the diagnosis of HCC recurrence by imaging methods was very important.

Aged↗
PubMed1993

Thermodynamics of G-tetraplex formation by telomeric DNAs.

Telomeres are structures at the ends of eukaryotic chromosomes, the DNA of which contains stretches of tandemly repeated sequences with G clusters along one strand. Model telomeric G-rich DNAs can form different tetraplex structures, stabilized by cyclic hydrogen bonding of four guanines in the presence of metal ions such as Na+ or K+. Oligonucleotides with a single copy of the Oxytricha sequence dT4G4 form a tetramer, with a parallel-stranded, right-handed helical structure. Additional copies favor folded-back structures that associate to form an antiparallel dimer. The parallel-stranded tetramer has all G's in the anti configuration, while the folded-back dimer has alternating syn and anti nucleotide conformations along each strand. Here we have constructed two G-tetraplex structures, containing identical G-tetrad base pairs, from oligonucleotides. One has the truncated telomeric sequence from Oxytricha, dG4T4G4, which forms an antiparallel G-quartet structure; the second is constrained to form a parallel G-strand arrangement by insertion of a 5'-p-5' linkage between two dT2G4 sequences. Each oligomer forms a defined G-tetraplex dimeric structure in the presence of Na+. The standard-state enthalpies, entropies, and free energy for formation of these tetraplexes have been determined. The parallel strand structure is thermodynamically more stable than the antiparallel one, primarily because of both greater enthalpy and entropy of formation. In addition, the two molecules differ in their interaction with sodium ions, reflecting a difference in ion binding and therefore in structure between the two forms.

Calorimetry, Differential Scanning↗
PubMed1993

Effect of qingyangshen on hippocampal alpha- and beta-tubulin gene expression during kainic acid induced epileptogenesis.

Using alpha- and beta- tubulin cDNA Probes and Northern blot hybridization technique, we analyzed the effect of intraperitoneally injected Qingyangshen (QYS), a traditional Chinese medicine with antiepileptic property, and diphenylhydrantoin sodium (DPH) on hippocampal alpha- and beta-tubulin gene expression during kainic acid (KA) induced chronic seizures. It was found that: 1) thirty days after intraperitoneal injection of KA, alpha- and beta-tubulin mRNAs in animals showing chronic seizures increased 3.02 +/- 1.05 and 4.07 +/- 1.32 times respectively compared with control; 2) neither QYS (15 mg/kg, q.o.d. x 6) nor DPH (50 mg/kg, q.o.d. x 6), when used separately, could inhibit the above mentioned effect of KA; 3) when QYS (15 mg/kg, q.o.d. x 6) and DPH (50 mg/kg, q.o.d. x 6) were given in combination, the long-term increase in tubulin gene expression induced by KA was significantly reduced, with alpha- and beta-tubulin mRNAs being decreased to 0.44 +/- 0.08 and 0.50 x 0.10 times of corresponding values in animals treated with KA alone. The results indicate that the mechanism of antiepileptic effect of QYS is at least partially related to the inhibition of tubulin synthesis and subsequent reduction in mossy fiber sprouting and neosynaptogenesis.

Animals↗
PubMed1993

[Tear malate dehydrogenase, lactate dehydrogenase, and their isoenzymes in normal Chinese subjects and patients of ocular surface disorders].

Levels of malate dehydrogenase (MDH), lactate dehydrogenase (LDH) and their isoenzymes in tears of normal Chinese subjects and patients with ocular surface disorders were determined. The normal values of tear LDH and MDH were found to be 45.51 +/- 23.00-81.35 +/- 37.84 mumol.s-1/L and 11.00 +/- 5.33-19.50 +/- 9.17 mumol.s-1/L respectively, disregarding sex or eye distinction. The LDH/MDH ratio reflected sensitively the metabolism of corneal and conjunctival epithelium. The MDH isoenzymes comprised MDHs and MDHm, the former accounting for 80.0%-89.1%. The LDH isoenzymes comprised 5 varieties, of which the ratio H/M of subunit H to subunit M was 0.196 +/- 0.02. The changes in LDH isoenzymes were helpful to the differential diagnosis of external eye diseases, and the increase of MDHm reflected sensitively the degree of injury to the corneal epithelium.

Adolescent↗
PubMed1993

Electrophysiological and pathological observations on experimental coxsackie B-3 viral myocarditis in mice.

Electrophysiological action of right ventricular myocardium examined by standard intracellular microelectrode technique and real-time microcomputer data processor system and histological and ultrastructural changes of myocardium in BALB/c mice infected with coxsackie B-3 virus from 3 days to 9 months were observed. It was found that electrophysiologic parameters of action potential changed very quickly at the early stage (3 days to 1 month) of the disease. Those abnormalities became most apparent by the 5-30th day, and 7 patterns of abnormal action potential occurred frequently within the same period. These changes were basically parallel to the myocardial lesions. At the late stage (3-9 months) the electrophysiological parameters were nearly normal, while the myocardial lesions decreased gradually. However, the abnormal patterns of action potential were still detected, even though they were improved gradually. The results suggest that myocardial damages caused by viral infection may lead to changes of cardiac electric action, which may be one of the factors in arrhythmias in the episode of viral myocarditis.

Action Potentials↗
PubMed1992

Adenine affects the structure and stability of telomeric sequences.

Adenine occurs in the strand containing repeated G clusters in the telomeric DNA of a variety of organisms, including that of humans. The role of adenine has been investigated by constructing two sets of oligonucleotides each with one, two, or four copies of the telomeric sequence dTTTAGGG together with a control sequence in which T replaces the A residue, dTTTTGGG. Comparison of the stability and spectral properties of these two sequences in the presence of Na+ or K+ affords a basis for defining the role of adenine in these structures. In Na+, the A residue stabilizes the structure formed by each oligomer significantly, presumably by a base-pairing interaction with T. In K+, by contrast, there is little difference in stability. In two- and four-copy oligomers, the A sequence has a different structure from its T analog, as detected by CD spectroscopy. In the presence of either Na+ or K+, the tetraplexes of A and T interact with intercalators.

Adenine↗
PubMed1992

Conformational properties of B-Z junctions in DNA.

The structural consequences of specific base sequences in DNA can exert a strong influence on the function of DNA. It has previously been reported that the presence of multiple B-Z conformational junctions in constructed DNA oligomers results in unusually enhanced electrophoretic gel mobilities of these oligomers [Winkle, S. A., & Sheardy, R. D. (1990) Biochemistry 29, 6514-6521]. In order to investigate this phenomenon further, we designed and synthesized several DNA oligomers capable of pure Z or B-Z junction formation for polyacrylamide gel electrophoresis studies. The results indicate that both pure Z-DNA and polymorphic B-Z-DNA oligomers exhibit unusual gel migratory properties. The results of gel mobility studies in the absence and presence of cobalt hexamine indicate that a B-Z junction corresponds to a stiff bend of the helix axis, with two or more conformers accessible at the junction site. This is a different bend and mechanism than that in oligo(A) tracts.

Base Sequence↗
PubMed1992

Interaction of the dye ethidium bromide with DNA containing guanine repeats.

DNA containing one or more copies of the motifs repeated in telomere sequences has unusual conformational properties. The isolated sequence from the protozoan Oxytricha, dT4G4 has the potential to form tetramers in the presence of sodium or potassium ions. We report here that these tetramers bind ethidium tightly, with an interaction that fulfills several criteria for an intercalative mechanism in the G sequence. By contrast, the 4-fold tandem repeat of this subunit, d(T4G4)4, does not interact specifically with ethidium in the presence of Na+. This difference might have a simple structural basis: the tetramer of dT4G4 forms a stack of four G-quartets in the presence of Na+ or K+, whereas the constraint imposed by the T4 "tethers" in the repeat d(T4G4)4 allows only two layers to form in the presence of Na+. In the presence of sufficient K+, the latter can partially form a four-layer G-quartet structure, which interacts with ethidium. This idea is supported by analysis of a "relaxed" sequence, dT4G4(T7G4)3, which allows formation of four G-quartets and binds ethidium in the presence of Na+ as well as K+. Ethidium (and intercalators generally) should thus be able to retard or inhibit the action of telomerase in the presence of K+.

Animals↗
PubMed1992

Structure and stability of sodium and potassium complexes of dT4G4 and dT4G4T.

The ends of eukaryotic chromosomes contain specialized structures that include DNA with multiple tandem repeats of simple sequences containing clusters of G on one strand, together with proteins which synthesize and bind to these sequences. The unit repeat in the protozoan Oxytricha with the cluster dT4G4 can form structures containing tetrads of guanine residues, referred to G4 DNA, in the presence of metal ions such as Na+ or K+. We show here that, in the presence of Na+, dT4G4 forms a tetramer with parallel strands by means of a UV cross-linking assay. In the presence of K+, two further interactions are observed: at low temperature, higher order complexes are formed, provided the 3' end of the strand is G; a single 3'T inhibits this association in dT4G4T. At high temperature, these complexes dissociate, leading to a tetramer with a different ordered structure that melts only at very high temperatures. These results suggest that the cohesive properties of DNA containing G clusters might depend on associative interactions driven by a free 3'G terminus in the presence of K+, as well as by connecting antiparallel G hairpins as has been postulated.

Circular Dichroism↗
PubMed1992

Thermodynamics of DNA branching.

Branched DNA molecules arise transiently as intermediates in genetic recombination or on extrusion of cruciforms from covalent circular DNA duplexes that contain palindromic sequences. The free energy of these structures relative to normal DNA duplexes is of interest both physically and biologically. Oligonucleotide complexes that can form stable branched structures, DNA junctions, have made it possible to model normally unstable branched states of DNA such as Holliday recombinational intermediates. We present here an evaluation of the free energy of creating four-arm branch points in duplex DNA, using a system of two complementary junctions and four DNA duplexes formed from different combinations of the same set of eight 16-mer strands. The thermodynamics of formation of each branched structure from the matching pair of intact duplexes have been estimated in two experiments. In the first, labeled strands are allowed to partition between duplexes and junctions in a competition assay on polyacrylamide gels. In the second, the heats of forming branched or linear molecules from the component strands have been determined by titration microcalorimetry at several temperatures. Taken together these measurements allow us to determine the standard thermodynamic parameters for the process of creating a branch in an otherwise normal DNA duplex. The free energy for reacting two 16-mer duplexes to yield a four-arm junction in which the branch site is incapable of migrating is + 1.1 (+/- 0.4) kcal mol-1 (at 18 degrees C, 10 mM-Mg2+). Analysis of the distribution of duplex and tetramer products by electrophoresis confirms that the free energy difference between the four duplexes and two junctions is small at this temperature. The associated enthalpy change at 18 degrees C is +27.1 (+/- 1.3) kcal mol-1, while the entropy is +89 (+/- 30) cal K-1 mol-1. The free energy for branching is temperature dependent, with a large unfavorable enthalpy change compensated by a favorable entropy term. Since forming one four-stranded complex from two duplexes should be an entropically unfavorable process, branch formation is likely to be accompanied by significant changes in hydration and ion binding. A significant apparent delta Cp is also observed for the formation of one mole of junction, +0.97 (+/-0.05) kcal deg-1 mol-1.

Base Composition↗
PubMed1992

A tyrosyl-tRNA synthetase binds specifically to the group I intron catalytic core.

The Neurospora CYT-18 protein, the mitochondrial tyrosyl-tRNA synthetase, functions in splicing group I introns in mitochondria. Here, we show that CYT-18 binds strongly to diverse group I introns that have minimal sequence homology and recognizes highly conserved structural features of the catalytic core of these introns. Inhibition experiments indicate that the intron RNA and tRNA(Tyr) compete for the same or overlapping binding sites in the CYT-18 protein. Considered together with functional analysis, our results indicate that the CYT-18 protein promotes splicing by binding to the intron core and stabilizing it in a conformation required for catalytic activity. Furthermore, the specific binding of the synthetase suggests that the group I intron catalytic core has structural similarities to tRNAs, which could reflect either convergent evolution or an evolutionary relationship between group I introns and tRNAs.

Base Sequence↗