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X Tang

Publications and source records attributed to X Tang.

At least 55 records · Page 3Linked to original sources
PubMed2000

Event-related potential N270 is elicited by mental conflict processing in human brain.

We recorded event-related potentials (ERPs) in 15 subjects in order to elicit a N270 of arithmetic conflict. Subjects calculated an arithmetic problem and matched their calculation result to an answer digit. They pressed a button when the presented digit is a true answer (condition 1) and pressed another button when the answer is false (condition 2). ERP components of P90, N130, P180, N200 and late positive component (LPC) were recorded in condition 1. In condition 2, N270 was elicited between N200 and LPC and it peaked at approximately 270 ms (268.6 +/- 29.0 ms at Cz). The peak latency of LPC in condition 2 (405.7 +/- 51.3 ms) is significantly delayed than condition 1 (307.5 +/- 22.7 ms). N270 reflects the endogenous conflict processing in human brain.

Adult↗
PubMed2000

Hypermethylation of the death-associated protein (DAP) kinase promoter and aggressiveness in stage I non-small-cell lung cancer.

BACKGROUND: Death-associated protein (DAP) kinase is a serine/threonine kinase that is important in ligand-induced programmed cell death and plays an important role in lung cancer metastasis in animal models. Hypermethylation of the promoter represses the expression of the DAP kinase gene. Our purpose was to determine whether the hypermethylation status of the DAP kinase promoter influences the prognosis of non-small-cell lung cancer (NSCLC). METHODS: We retrospectively studied 135 patients with pathologic stage I NSCLC who had undergone curative surgery. Methylation-specific polymerase chain reaction was used to determine the methylation status of the DAP kinase promoter in resected specimens from patients with primary NSCLC. Statistical analyses, all two-sided, were performed to determine the prognostic effect of methylation status on various clinical parameters. RESULTS: Hypermethylation of the DAP kinase promoter was found in 59 (44%) of the 135 tumors. Patients whose tumors exhibited such hypermethylation had a statistically significantly poorer probability of overall survival at 5 years after surgery than those without such hypermethylation (.46 versus.68; P: =.007). Moreover, the groups with and without hypermethylation of the DAP kinase promoter showed a striking difference in the probability of disease-specific survival; i.e., among people who died of lung cancer-related causes specifically, the probability of 5-year survival was.56 for those with such hypermethylation and.92 for those without it (P:<.001). Multivariate analysis indicated that hypermethylation of the DAP kinase promoter is the only independent predictor for disease-specific survival among clinical and histologic parameters tested. CONCLUSIONS: Hypermethylation of the DAP kinase promoter is a common abnormality in early-stage NSCLC. This abnormality is strongly associated with survival, suggesting that DAP kinase plays an important role in determining the biologic aggressiveness of early-stage NSCLC.

Adenocarcinoma↗
PubMed2000

Enhanced oncogenicity of human papillomavirus type 16 (HPV16) variants in Japanese population.

To investigate whether HPV16 E6 variants carry an elevated risk for cervical cancer in Japanese population, we investigated the E6 sequence variation in 40 cervical intraepithelial neoplasias (CINs) I-III and 43 invasive cervical cancers (ICCs), all positive for HPV16. HPV16 E6 variants were frequently found in ICCs than in CINs (88 vs. 65%, P=0.01). The E6 D25E, a rare variant in Western countries, was most frequently observed in ICC (44%). CIN I/II lesions with HPV16 variants were less likely to regress than those with HPV16 prototype (P=0.048). The finding that HPV16 E6 variants represent a significant risk factor is common between Western and Japanese women despite the different distribution of each variant.

Base Sequence↗
PubMed2000

Bgs2p, a 1,3-beta-glucan synthase subunit, is essential for maturation of ascospore wall in Schizosaccharomyces pombe.

Previously we have reported that Drc1p/Cps1p, a 1,3-beta-glucan synthase subunit, is essential for division septum assembly in Schizosaccharomyces pombe. In this report, we present evidence that S. pombe Bgs2p, a 1,3-beta-glucan synthase that shows 56% identity to Drc1p/Cps1p, is essential for maturation of ascospore wall in S. pombe, but is not required for vegetative growth. Diploid cells homozygous for the bgs2-null mutation, as well as homothallic bgs2-null mutant haploids undergo meiosis normally. However, a 1, 3-beta-glucan containing spore wall is not assembled in these cells. The spores resulting from meiosis of a bgs2-null mutant lyse upon release from the ascus and are therefore inviable. Using a green fluorescent protein-tagged Bgs2p, we demonstrate that Bgs2p is localized at the periphery of the ascospores during meiosis and sporulation. However, Bgs2p is not detected in vegetative cells. We conclude that Bgs2p is required for 1,3-beta-glucan synthesis during ascospore wall maturation.

Cell Division↗
PubMed2000

Role of phosphatidylinositol 3-kinase and specific protein kinase B isoforms in the suppression of apoptosis mediated by the Abelson protein-tyrosine kinase.

Leukemogenic oncogenes, such as the Abelson protein-tyrosine kinases (PTK), disrupt the normal regulation of survival, proliferation, and differentiation in hemopoietic progenitor cells. In the absence of cytokines, hemopoietic progenitor cells die by apoptosis. Abl PTKs mediate suppression of this apoptotic response leading to aberrant survival. To investigate the mechanism of Abl PTK action, we have used an interleukin-3-dependent murine mast cell line that expresses a temperature-sensitive form of the v-ABL PTK, which is active at the permissive temperature of 32 degrees C and inactive at 39 degrees C. At the permissive temperature, these cells are resistant to apoptosis induced both by the withdrawal of the hemopoietic growth factor (interleukin-3) and the addition of cytotoxic drugs. We demonstrate that v-Abl associates with and stimulates activation of phosphatidylinositol 3-kinase (PI3K) and, crucially, that this activation results in enhanced cellular levels of the mass of the second messenger phosphatidylinositol-3,4,5-trisphosphate. Activation of PI3K leads to enhanced activity of PKB and increased levels of the anti-apoptotic protein Bcl-X(L). Transfection of cells with a dominant negative PKB reduces both the Abl-stimulated PKB activity and the survival effect conferred by activation of this oncogene. Thus, PI3K and PKB are required for the anti-apoptotic effects of Abl PTK.

Animals↗
PubMed2000

Electronic structures of single-walled carbon nanotubes determined by NMR

Single-walled carbon nanotubes were studied by (13)C nuclear magnetic resonance (NMR). Two types of (13)C nuclear spins were identified with different spin-lattice relaxation rates. The fast-relaxing component, assigned to metallic tubes, followed the relaxation behavior expected in metals, and the density-of-states at the Fermi level increased with decreasing tube diameter. The slow-relaxing component has a significantly lower density-of-states at the Fermi level. Exposure to oxygen has a substantial effect on relaxation rates of both components.

Journal Article↗
PubMed2000

Phospholipase D: molecular and cell biology of a novel gene family.

Interaction of extracellular-signal molecules with cell-surface receptors often activates a phospholipase D (PLD)-mediated hydrolysis of phosphatidylcholine and other phospholipids, generating phosphatidic acid. The activation of PLD is believed to play an important role in the regulation of cell function and cell fate. Multiple PLD activities were characterized in eukaryotic cells, and, more recently, several PLD genes have been cloned. A PLD gene superfamily, defined by a number of structural domains and sequence motifs, also includes phosphatidyltransferases and certain phosphodiesterases. Among the eukaryotic PLD genes are those from mammals, nematodes, fungi and plants. The present review focuses on the structure, localization, regulation and possible functions of cloned mammalian and yeast PLDs. In addition, an overview of plant PLD genes, and of several distinct PLD activities that have not yet been cloned, is provided. Emerging evidence from recent work employing new molecular tools indicates that different PLD isoforms are localized in distinct cellular organelles, where they are likely to serve diverse functions in signal transduction, membrane vesicle trafficking and cytoskeletal dynamics.

Animals↗
PubMed2000

Primary structure of Noetia ponderosa hemoglobins: functional correlates.

Homo- and heterodimeric hemoglobins have been isolated from the red cells of the arcid clam Noetia ponderosa (Np). These hemoglobins bind oxygen cooperatively. An extensively studied dimeric hemoglobin from another arcid clam, Scapaharca inaequivalvis, exhibits a molecular mechanism for cooperative ligand binding that is radically different from tetrameric vertebrate hemoglobins. In this study, the two chains found in both Noetia hemoglobins are sequenced and compared to the hemoglobins of the related clam S. inaequivalvis to determine whether Noetia hemoglobins have the structural basis for the same unusual mechanism for cooperative ligand binding and to inquire about the structural basis of absence of tetramers. Although the Noetia sequences are homologous to the Scapharca sequences, critical differences exist. The lack of tetramerization of Np subunits is most likely related to the absence of critical residues in the A and G helices that stabilize the interdimer contact seen in the Scapharca Hb tetramer. The lower affinity of the homodimer (Np-I), but particularly the heterodimer (Np-II) with respect to the homodimer and heterotetramer of Scapharca, can be due to (i) changes in the proximal heme environment and (ii) changes in the dimer interface. Interactions between Asn 100 and the heme of the other subunit are altered in Np-II due to the substitution of this residue by methionine, possibly causing the reduced O(2) affinity of the heterodimer of Noetia. (iii) Sequence changes in the E and F helices present in Np-I and Np-II could also contribute to the effect through interfacial changes. In particular, the substitution of Val for Thr in position 72 is expected to have a substantial influence on the interface. We conclude that Np dimers have the structural basis for a direct heme-heme interaction mechanism for cooperativity, as in Scapharca, but there are enough sequence changes to suggest that the pathway of interaction might be somewhat different.

Amino Acid Sequence↗
PubMed2000

Cryopreservation of rhesus macaque (Macaca mulatta) spermatozoa and their functional assessment by in vitro fertilization.

Although spermatozoa from several species of nonhuman primates have been cryopreserved, there has been no report of success with rhesus macaque spermatozoa as judged by functional assays. Two Tris--egg yolk freezing media, TEST and TTE, which have been successfully used for cynomolgus macaque (Macaca fascicularis) spermatozoa, were compared for cryopreservation of spermatozoa from four rhesus macaques (Macaca mulatta). The postthaw motility (percentage and duration) of spermatozoa cryopreserved in TTE was much higher than that for spermatozoa cryopreserved in TEST. The function of sperm cryopreserved in TTE was evaluated by in vitro fertilization of oocytes collected from gonadotropin-stimulated prepubertal rhesus macaques. Of the inseminated oocytes, 82 +/- 13% were fertilized and 63 +/- 22 and 39 +/- 21% of the resulting zygotes developed into morulae and blastocysts, respectively. These results indicate that rhesus macaque spermatozoa can be effectively cryopreserved in TTE medium. This finding will facilitate the application of in vivo and in vitro assisted reproductive technologies in this species.

Animals↗
PubMed2000

Wavelet transforms in estimating scatterer spacing from ultrasound echoes.

Ultrasound echoes from organs such as the liver display resolvable periodicity due to regular scattering centers within tissue. The spacing among such scattering centers has been proposed as a signature to characterize diffuse and focal diseases of the liver. Even though it is highly desirable to be able to estimate an inter-scatterer-spacing (ISS) distribution, current methods can estimate only the mean value of scatterer spacing (MSS) over a tissue length. In this paper, we propose a wavelet transform-based technique that is capable of estimating the location of each scattering center, making it possible to obtain the ISS distribution. We represent liver tissue with a point scatterer model, and show, via computer simulations, that the use of multi-scale information in the wavelet scale-space allows us to estimate the locations of regular scattering centers. We show that both the observation noise and random ultrasound returns from unresolvable tissue microstructure can be removed successfully in the wavelet domain via the properties of the modulus maxima sequence of observation across different scales.

Computer Simulation↗
PubMed2000

Detection of integrins in cataract lens epithelial cells.

PURPOSE: To detect the expression of integrin subunits in lens epithelial cells (LECs) of human cataracts. SETTING: Research Laboratory, International Intraocular Implant Training Centre, Tianjin Medical University, China. METHODS: The circular sections of the anterior capsules with attached LECs were obtained during cataract surgery from 100 patients. The LECs were stained with an avidin-biotin-complex immunohistochemical technique using 5 monoclonal antibodies specific for alpha subunits 2, 3, 5 and beta subunits 1, 2. RESULTS: All integrin subunits studied were found to varying degrees in specimens. The positive percentages were 70%, 65%, 75%, 70%, and 80%, respectively. CONCLUSION: Integrin subunits were present in LECs of human cataracts. These molecules may serve in the adhesion of LECs to the lens capsule and play a role in cell-posterior capsule interaction after cataract surgery.

Antibodies, Monoclonal↗
PubMed2000

Changes of microsomal membrane properties in spring wheat leaves (Triticum aestivum L.) exposed to enhanced ultraviolet-B radiation.

The properties of microsomal membranes in spring wheat leaves (Triticum aestivum L. cv. Ganlong No. 92-005) exposed to (0) control, 8.64 (T1) and 11.2 kJ m(-2) day(-1) (T2) biologically effective UV-B irradiation (UV-B(BE)) were studied under greenhouse conditions. These irradiance levels correspond to a decrease in the stratospheric ozone of approximately 12.5 and 20%, respectively, for a clear solstice day at Lanzhou (36.04 degrees N, 1550 m), China. Compared with controls, the content of malondialdehyde (MDA) increased by 70.8% in T1 and 83.8% in T2 on the 7th day of the radiation, and the IUFA (index of unsaturated fatty acids) decreased, indicating peroxidation of lipid acids. Simultaneously, a drastic decrease of phospholipid content after 21 days and an increase of membrane lipid microviscosity on UV-B irradiation were also found, suggesting a reduction in the fluidity of membrane lipids. Ethylene emission by the microsomal membrane, in the presence of exogenous 1-aminocyclopropane-1-carboxylic acid was higher in the wheat seedlings after 7, 14 and 21 days' irradiation than in the controls. These changes were correlated with a rise in lipoxygenase activity. Membrane-bound enzymes (Ca2+ -ATPase and Mg2+ -ATPase) were promoted by UV radiation in the first 7 days and significantly decreased after 14 and 21 days' treatment in comparison to control. Our results suggest that UV-B radiation may cause changes in structural complexity and function of microsomal membranes in spring wheat leaves.

Dose-Response Relationship, Radiation↗
PubMed2000

MR volumetric analysis of the human basal ganglia: normative data.

RATIONALE AND OBJECTIVES: The authors undertook this study to identify a precise, semiautomated, reproducible magnetic resonance (MR) imaging technique for measuring the basal ganglia, to establish normative volumetric data, and to verify the presence of previously reported asymmetries. MATERIALS AND METHODS: Twenty-eight healthy adults underwent cranial MR examination. The volumes of the various components of the basal ganglia were measured by means of a combination of thresholding and manual tracing techniques performed with specialized software. The validity of these measurements was assessed by fashioning, imaging, and measuring a practical basal ganglia phantom. Measurement accuracy was also established by means of inter- and intrarater reliability indexes. Normalized volumes were statistically analyzed with analysis of variance and paired t tests. RESULTS: The absolute values of the various components of the basal ganglia varied widely even though the volumes were normalized to differences in intracranial volume. The right caudate nucleus volume was significantly (P < .000001) larger than the left in both men and women and in both right-handed and non-right-handed subjects. This asymmetry led to an increase in the overall volume of the basal ganglia on the right. CONCLUSION: The authors have defined a precise, reproducible technique for measuring various components of the basal ganglia and have established normative data. The basal ganglia, similar to other brain structures, exhibit hemispheric lateralization.

Adult↗
PubMed2000

Type II myosin regulatory light chain relieves auto-inhibition of myosin-heavy-chain function.

The F-actin based motor protein myosin II has a key role in cytokinesis. Here we show that the Schizosaccharomyces pombe regulatory light chain (RLC) protein Rlc1p binds to Myo2p in manner that is dependent on the IQ sequence motif (the RLC-binding site), and that Rlc1p is a component of the actomyosin ring. Rlc1p is important for cytokinesis at all growth temperatures and is essential for this process at lower temperatures. Interestingly, all deleterious phenotypes associated with the loss of Rlc1p function are suppressed by deletion of the RLC binding site on Myo2p. We conclude that the sole essential function of RLCs in fission yeast is to relieve the auto-inhibition of myosin II function, which is mediated by the RLC-binding site, on the myosin heavy chain (MHC).

Amino Acid Sequence↗
PubMed2000

A novel composite locus of Arabidopsis encoding two polypeptides with metabolically related but distinct functions in lysine catabolism.

Both plants and animals catabolize lysine via saccharopine by two consecutive enzymes, lysine-ketoglutarate reductase (LKR) and saccharopine dehydrogenase (SDH), which are linked on a single polypeptide. We recently demonstrated that Arabidopsis plants possess not only a bifunctional LKR/SDH but in addition a monofunctional SDH enzyme. We also speculated that these two enzymes may be controlled by a single gene (G. Tang et al. Plant Cell, 1997, 9, 1305-1316). By expressing several epitope-tagged and GUS reporter constructs, we demonstrate in the present study that the Arabidopsis monofunctional SDH is encoded by a distinct gene, which is, however, nested entirely within the coding and 3' non-coding regions of the larger bifunctional LKR/SDH gene. The entire open reading frame of the monofunctional SDH gene, as well as some components of its promoter, are also parts of the translated coding sequence of the bifunctional LKR/SDH gene. These special structural characteristics, combined with the fact that the two genes encode simultaneously two metabolically related but distinct enzymes, render the LKR/SDH locus a novel type of a composite locus. Not all plant species possess an active monofunctional SDH gene and the production of this enzyme is correlated with an increased flux of lysine catabolism. Taken together, our results suggest that the composite LKR/SDH locus serves to control an efficient, highly regulated flux of lysine catabolism

Amino Acid Sequence↗
PubMed2000

Diagnosis of Pneumocystis carinii pneumonia in human immunodeficiency virus-infected patients with polymerase chain reaction: a blinded comparison to standard methods.

Pneumocystis carinii pneumonia (PCP) is an important cause of morbidity and death among persons with human immunodeficiency virus (HIV) infection. Polymerase chain reaction (PCR) analysis of respiratory specimens has been investigated as a rapid diagnostic method. We have previously reported on the utility of this technique for diagnosing PCP in HIV-infected patients. In this report we evaluate PCR used in a blinded study design to avoid biases inherent to retrospective and nonblinded studies. The diagnosis of PCP was established on the basis of clinical findings and morphological studies of bronchoalveolar lavage (BAL) and/or lung biopsy specimens before PCR testing. PCR was performed without knowledge of the diagnosis. PCR results were graded from "negative" to 3+ on the basis of intensity of the banding pattern. Forty-seven patients were enrolled in the study, including 18 with proven PCP and 29 with other conditions. PCR was positive at grade 1 or higher for all 18 patients with PCP (100% sensitivity), at grade 2 or higher for 13 patients (72.2% sensitivity), and at grade 1 or higher for 4 of the 29 control patients (specificity of 86.2%). If a grade 2 or higher was required for diagnosis, the specificity improved to 100%. Results were reproducible with testing of a second aliquot for 46 of 47 patients (97.8%). Our findings confirm that PCR is a sensitive and reproducible test for detection of P. carinii in BAL specimens. Problems with false-positive results for control patients, however, limit the applicability of this method.

AIDS-Related Opportunistic Infections↗