Biomedical subjects

L Li

Publications and source records attributed to L Li.

At least 829 records · Page 46Linked to original sources

PubMed1999

Negative modulation of alpha1(I) procollagen gene expression in human skin fibroblasts: transcriptional inhibition by interferon-gamma.

Interferon-gamma (IFN-gamma), a multifunctional cytokine produced by activated Th1 lymphocytes, exerts potent effects on the extracellular matrix by regulating fibroblast function. In this study, we examined the modulation of alpha1(I) procollagen gene (COL1A1) expression by recombinant IFN-gamma. The results showed that IFN-gamma stimulated the rapid accumulation of interferon regulated factor (IRF)-1 mRNA, followed by a delayed and dose-dependent inhibition of alpha1(I) procollagen mRNA expression in skin fibroblasts from several different donors. The inhibitory response was abrogated in fibroblasts stably expressing IRF-1 in the antisense orientation. A marked decrease in the amount of heterogeneous nuclear pre-mRNA preceded the inhibition of COL1A1 mRNA expression. In fibroblasts transiently transfected with COL1A1 promoter-chloramphenicol acetyltransferase reporter gene plasmids, IFN-gamma selectively inhibited promoter activity and abrogated its stimulation induced by TGF-beta. The inhibition by IFN-gamma was not due to downregulation of TGF-beta receptor mRNA expression in the fibroblasts or decreased ligand binding to the receptor. IFN-alpha and IFN-beta by themselves had little effect on promoter activity, but IFN-alpha augmented the inhibitory effect of IFN-gamma. Using a series of 5' deletion constructs, a proximal region of the COL1A1 promoter was shown to function as an IFN-gamma response element. This region of the gene harbors overlapping binding sites for transcription factors Sp1, Sp3, and NF-1 but no homologs of previously characterized IFN-gamma response elements. The putative IFN-gamma response region was sufficient to confer inhibition of reporter gene expression by treatment with IFN-gamma. Gel mobility shift analysis showed that two distinct and specific DNA-protein complexes were formed when fibroblast nuclear extracts were incubated with oligonucleotides spanning the IFN-gamma response region. IFN-gamma did not modify the ability of nuclear proteins to bind to this region. The results indicate that IFN-gamma inhibits COL1A1 expression in fibroblasts principally at the level of gene transcription. Inhibition involves IRF-1 and is mediated through a short proximal promoter segment but without an apparent change in promoter occupancy. The findings provide novel insight into the mechanism of IFN-gamma regulation of fibroblast function.

Adult↗

PubMed1999

An estimate of the crosstalk matrix in four-dye fluorescence-based DNA sequencing.

Color separation is an essential step of the data processing in the four-dye fluorescence detection strategy used in automated DNA sequencing. In this paper, we propose a model to describe the crosstalk phenomenon, and show how the assumptions of the model are supported by experimental data. The crosstalk matrix is estimated via a reparameterization based on a mapping between the distribution of fluorescence intensities and that of dye concentrations. An iterative algorithm is designed to implement the estimation. To evaluate the color-correction quality of a crosstalk matrix, we propose a quantitative measure based on the distribution of the color-corrected data. We illustrate this method by applying it to a sequencing trace of slab gel electrophoresis obtained at the Human Genome Center at Lawrence Berkeley National Laboratory, and that of capillary electrophoresis provided by the Department of Chemistry at UC, Berkeley. The accuracy of this method is also assessed by the bootstrap method.

Algorithms↗

PubMed1999

New Vibrational Numbering and Potential Energy Curve for the 3(3)Pig Electronic State of the Li2 Molecule.

An experimental study of the 3(3)Pig electronic state of 7Li2, using the Perturbation-Facilitated Optical-Optical Double Resonance (PFOODR) technique, was recently reported [A. Yiannopoulou et al., J. Chem. Phys. 103, 5898, (1995)]. However, due to the very small number of known 7Li2 A1Sigma+u approximately b3Piu window levels, only 13 ro-vibrational levels (spanning a range of vibrational levels designated upsilonx - 1 to upsilonx + 3 in that reference) could be observed. Dunham coefficients, based on the assignment upsilonx = 7, were found to fit the observed term values and give a qualitative fit to the intensities of the first six lines of the 3(3)Pig (upsilon = upsilonx, N = 11) --> b3Piu emission spectrum. However, due to the limited number of levels used in the fit, both the absolute vibrational numbering and the 3(3)Pig RKR potential curve obtained from the Dunham coefficients, must be considered to be uncertain. In the present work, we show that the previously reported 3(3)Pig RKR curve is unable to reproduce the experimental intensity distribution in the 7Li2 3(3)Pig (upsilonx = 7, N = 11) --> a3Sigma+u emission continuum. We report new experimental data for the 7Li2 3(3)Pig (upsilonx + 1, N = 11) --> a3Sigma+u bound-free continuum and discrete 3(3)Pig (upsilonx +/- 1, N = 11) --> b3Piu spectra obtained using the PFOODR experimental technique. We demonstrate that the correct vibrational numbering and an improved RKR potential curve can be obtained by analyzing the experimental term values in combination with all observed bound-free and discrete spectra. Finally, term values for four 6Li2 3(3)Pig ro-vibrational levels were obtained using PFOODR spectroscopy. The measured isotope shifts confirm the absolute vibrational numbering obtained from the present analysis. Copyright 1999 Academic Press.

Journal Article↗

PubMed1999

The High-Lying Vibrational Levels and Dissociation Energy of the a3Sigma+u State of 7Li2.

Perturbation-facilitated optical-optical double resonance (PFOODR) has been used to access the 2(3)Pig state of 7Li2 via the excitation scheme using two single-mode tunable lasers. The selected () mixed level provides a gateway through which the triplet manifold can be accessed. Fluorescence from single rovibrational levels of 2(3)Pig to the state was detected at high resolution using a Fourier transform spectrometer. Transitions to v = 0-9 in the state were observed, covering the potential well almost to the dissociation limit. The data were analyzed using a near dissociation expansion (NDE) technique and the resulting vibrational and rotational parameters were used to calculate a new RKR potential curve which reproduced the observed energy levels to within a rms error of 0.02 cm-1. The following parameters were obtained for the state: D0 = 301.829 +/- 0.015 cm-1, De = 333.69 +/- 0.10 cm-1, Te = 8183.12 +/- 0.12 cm-1. Copyright 1999 Academic Press.

Journal Article↗

PubMed1999

Rotational Pattern Difference in Resolved Fluorescence Spectra with Different Detection Schemes.

The relative intensities of rotational lines in resolved fluorescence spectra are dependent on the detection direction and the choice of the detection scheme when a grating monochromator is used. These differences arise from the spatially anisotropic distribution of the fluorescence, the rotational branch dependence of the fluorescence polarization, and the polarization dependence of the monochromator grating efficiency. Both the anisotropy of the emission and the rotational branch dependence of the fluorescence polarization are enhanced in double-resonance excitation schemes. In the present work, we analyze the relative intensities in the (7)Li(2) 1(3)Sigma(-)(g) --> 1(b)(3)Pi(u) and 1(3)Delta(g) --> 1(b)(3)Pi(u) resolved fluorescence spectra, observed following double-resonance excitation, for three different detection schemes. Copyright 1999 Academic Press.

Journal Article↗

PubMed1999

The 4(3)Pi(g) State of Na(2): Vibrational Numbering and Hyperfine Structure.

The Na(2) 4(3)Pi(g) state has been studied by continuous-wave (cw) perturbation-facilitated optical-optical double resonance (PFOODR) fluorescence excitation and resolved fluorescence spectroscopy. The absolute vibrational numbering was determined by resolved fluorescence to the a(3)Sigma(+)(u) state. The OODR excitation lines of the 4(3)Pi(g) (Kv, N) <-- b(3)Pi(u) (Kv(b)('), J') approximately A(1)Sigma(+)(u) (Kv(A)('), J') <-- X(1)Sigma(+)(g) (Kv", J") transitions show hyperfine splittings, and the hyperfine coupling scheme of the upper 4(3)Pi(g) levels is case b(betaS). Although this 4(3)Pi(g) state dissociates to the 3p + 3p atomic limit, it is a Rydberg state at a small internuclear distance, and the hyperfine splitting is caused mainly by the Fermi contact interaction of the varsigma(g)3s valence electron with the nuclei. The Fermi contact constant was determined to be b(F) = 218.3 +/- 3.9 MHz. Copyright 1999 Academic Press.

Journal Article↗

PubMed1999

The 6svarsigma, 6dvarsigma, and 7dvarsigma Rydberg (1)Sigma(+)(g) States and Two Doubly Excited (1)Sigma(+)(g) States of Na(2).

Five highly excited (1)Sigma(+)(g) states of Na(2) were observed for the first time by pulsed optical-optical double resonance (OODR) fluorescence excitation spectroscopy. Three of the five states are assigned to the 6svarsigma (1)Sigma(+)(g), 6dvarsigma (1)Sigma(+)(g), and 7dvarsigma (1)Sigma(+)(g) Rydberg states. The other two states are assigned to doubly excited (1)Sigma(+)(g) states. Copyright 1999 Academic Press.

Journal Article↗

PubMed1999

8-10svarsigma, 8-10dvarsigma (1)Sigma(+)(g), and 10-15dpi (1)Pi(g) Rydberg States of Na(2).

With a sensitive space-charge-limited diode ionization detector, we studied 8-10svarsigma, 8-10dvarsigma (1)Sigma(+)(g), and 10-15dpi (1)Pi(g) Rydberg states of Na(2) and obtained their molecular constants for the first time. It is the first successful example of a diode ionization detector that is used in a pulsed OODR molecular spectroscopy experiment. Copyright 1999 Academic Press.

Journal Article↗

PubMed1999

Agonist-stimulated calcium entry in primary cultures of human cerebral microvascular endothelial cells.

Primary cultures of human cerebral microvascular endothelial cells (HCMEC) were loaded with fura-2. The intracellular free Ca2+ concentration ([Ca2+]i) was measured by digital imaging microscopy. Agonists ATP (100 micro), thrombin (10 units/ml), and histamine (25 microM) induced a transient [Ca2+]i increase. Histamine (100 microM) induced a biphasic [Ca2+]i increase with an initial [Ca2+]i peak followed by a [Ca2+]i plateau. The [Ca2+]i plateau was blocked by the receptor-operated Ca2+ channel (ROC) blockers SK&F 96365 and NCDC, indicating a contribution by Ca2+ influx through ROC to the [Ca2+]i plateau. However, this [Ca2+]i plateau was not blocked by the voltage-gated Ca2+ channel (VGC) blocker diltiazem (DTZ). Depolarization with 80K+ or application of the VGC agonist BAY K 8644 did not alter the resting [Ca2+]i; but 80K+ reduced the histamine (100 microM) induced [Ca2+]i plateau. These results show that HCMEC are devoid of functional VGC. Thus the membrane potential (Em) regulates Ca2+ entry mainly by enhancing the electrochemical Ca2+ gradient, such that hyperpolarization increases while depolarization decreases [Ca2+]i. Blockade of sarcoplasmic/endoplasmic reticulum Ca2+-ATPase (SERCA) by CPA increased [Ca2+]i. This effect was dependent on extracellular Ca2+ and reduced by iberiotoxin (IBTX) blockade of Ca2+-activated K+ channels (Kca), suggesting a role for Kca in regulating Ca2+ influx. Ca2+ is the principal activator of endothelial nitric oxide synthase (eNOS), which stimulates cyclic GMP production. The final result that the eNOS inhibitor L-NAME enhanced the histamine (100 microM) induced [Ca2+]i plateau suggests a negative feedback loop (via cGMP) of endothelial NO on its own synthesis in the regulation of endothelial [Ca2+]i signal.

Adenosine Triphosphate↗

PubMed1999

High-level expression, purification, and characterization of recombinant type A botulinum neurotoxin light chain.

Botulinum neurotoxin light chain (BoNT LC, 50 kDa) is responsible for the zinc endopeptidase activity specific for proteins of neuroexocytosis apparatus. We describe the expression of recombinant type A BoNT LC in Escherichia coli as well as the purification and characterization of the recombinant protein. A high level of expression of BoNT/A LC was obtained by an extended postinduction time of 15 h at 30 degrees C. Recombinant BoNT/A LC was isolated from an Ni(2+) column. Due to its high pI ( approximately 8.7), purification was achieved by a single step of passing the protein through anion-exchange chromatography at pH 8.0 without the need of elution. The purified recombinant BoNT/A LC retained proteolytic activity and had a secondary structure similar to that of native LC determined by CD measurement.

Botulinum Toxins, Type A↗

PubMed1999

Reduction of tumorigenicity by an interferon-gamma-gene-transduced tumor on another syngeneic tumor in a murine model.

To evaluate the effect of interferon-gamma-gene-transduced cells, DS mice were inoculated into their footpads with syngeneic mammary adenocarcinoma SC42 admixed with interferon-gamma producing mammary adenocarcinoma SC115Kgamma, which had been established by an interferon-gamma-gene transduction in another syngeneic mammary adenocarcinoma SC115 using retroviral vectors. These mice rejected both tumor cells and developed resistance to subsequent challenges with either SC115 or SC42 cells inoculated into their opposite posterior footpads. These results thus indicate that systemic immunological memory to each of the independent tumor cell lines developed in these mice. Although the SC42 cells admixed with irradiated SC115Kgamma cells were rejected by these mice, the SC42 cells admixed with irradiated SC115neoR, in which the neo-gene had been transduced, were observed to proliferate. Tumor rejection was reversed by an in vivo administration of anti-interferon-gamma antibody, thus suggesting that locally produced interferon-gamma plays an important role in tumor elimination and immunological memory induction. In conclusion, interferon-gamma-gene-transduced tumor cells are therefore considered to have a therapeutic potential for other types of malignant tumor cell lines.

Adenocarcinoma↗

PubMed1999

Microbial Diversity in Sediments Collected from the Deepest Cold-Seep Area, the Japan Trench.

: The Japan Trench land slope at a depth of 6,400 m is the deepest cold-seep environment with Calyptogena communities. Sediment samples from inside and beside the Calyptogena communities were collected, and the microbial diversity in the sediment samples was studied by molecular phylogenetic techniques. From DNA extracted directly from the sediment samples, 16S rDNAs were amplified by the polymerase chain reaction method. The sequences of the amplified 16S rDNAs selected by restriction fragment length polymorphism analysis were determined and compared with sequences in DNA databases. The results showed that 33 different bacterial 16S rDNA sequences from the two samples analyzed fell into similar phylogenetic categories, the alpha-, gamma-, delta-, and varepsilon-subdivisions of Proteobacteria, Cytophaga, and gram-positive bacteria; some of the 16S rDNA sequences were common to both samples. delta- and varepsilon-Proteobacteria-related sequences were abundant in both sediments. These sequences are mostly related to sulfate-reducing or sulfur-reducing bacteria and epibionts, respectively. Eight different archaeal 16S rDNA sequences were cloned from the sediments. The majority of the archaeal 16S rDNA sequences clustered in Crenarchaeota and showed high similarities to marine group I archaeal rDNA. A Methanococcoides burtonii-related sequence obtained from the sediment clustered in the Euryarchaeota indicating that M. burtonii-related strains in the area of Calyptogena communities may contribute to production of methane in this environment. From these results, we propose a possible model of sulfur circulation within the microbial community and that of Calyptogena clams in the cold-seep environment.

Journal Article↗

PubMed1999

Rat C peptide I and II stimulate glucose utilization in STZ-induced diabetic rats.

AIMS: To study the effects of physiological concentrations of rat proinsulin C peptide I and II, respectively, on whole body glucose utilization in streptozotocin diabetic and healthy rats. METHODS: A sequential insulin clamp procedure was used (insulin infusion rates 3.0 and 30.0 mU.kg-1.min-1) in awake animals. C-peptide infusion rates were 0.05 and 0.5 nmol.kg-1.min-1. Blood glucose was clamped at 7.7 +/- 0.3 mmol/l in the diabetic rats and at 3.9 +/- 0.1 mmol/l in the healthy rats. RESULTS: In diabetic rats infused at lower rates of C peptide and insulin, glucose utilization increased by 79-90% (p < 0.001) compared with diabetic animals infused with saline and insulin. Increasing the rate of C-peptide infusion tenfold did not elicit a statistically significant further increase in glucose utilization. C peptide I and II exerted similar effects. The metabolic clearance rate for glucose in the diabetic animals infused with C peptide was not different from that of the healthy rats. During high-dose insulin infusion (30.0 mU.kg-1.min-1) glucose utilization increased considerably and no statistically significant C-peptide effects were observed. About 85% of the increase in glucose utilization induced by C peptide could be blocked by treatment with N-monomethyl-L-arginine. CONCLUSIONS/INTERPRETATION: Physiological concentrations of homologous C peptide stimulate whole body glucose utilization in diabetic but not in healthy rats. C peptide I and II elicit similar effects. The influence of C peptide on glucose utilization may be mediated by nitric oxide.

Animals↗

PubMed1999

The MHC of a broiler chicken line: serology, B-G genotypes, and B-F/B-LB sequences.

Although the major histocompatibility complex of chickens (encoded in the B complex) has been studied for a number of years, almost all work has focused on the White Leghorn breed. Broiler (meat-type) chickens were derived from other breeds, including Cornish and Plymouth Rock. It was our hypothesis that new B haplotypes, not previously identified in White Leghorns, might be present in lines of broiler chickens. Furthermore, alloantisera used to identify B serotypes in Leghorn lines reportedly do not work well outside the line in which they were raised, with the result that broiler B haplotypes have not been incorporated into the universal nomenclature system. Our approach was to use a panel of B alloantisera produced to identify B serotypes within a commercial broiler breeder line (designated line A). B homozygotes identified serologically were compared by B-G genotyping using restriction fragment length polymorphism analysis. Furthermore, reverse transcription-polymerase chain reaction was used to amplify variable domains of expressed B-LB and B-F genes of homozygotes of most of the B serotypes in Line A, followed by cloning and nucleotide sequence determination. Comparison of B-LB and B-F sequences with standard Leghorn haplotypes demonstrated the existence of new alleles of B-L and B-F in a broiler breeder line, as well as the presence of alleles previously identified in Leghorns. In some cases, Leghorn-type alleles were in linkage with different B-G alleles in the broiler line than the common haplotypic associations found in Leghorn lines.

Alleles↗

PubMed1999

Homolog pairing and meiotic progression in Coprinus cinereus.

We have used fluorescence in situ hybridization to examine homolog pairing during the synchronous meiosis of the basidiomycete Coprinus cinereus. Using spread preparations of meiotic nuclei, we confirmed previous studies that showed that at 6 h post-karyogamy essentially all meiotic nuclei are in pachytene. We found that homolog pairing occurs rapidly after karyogamy, that a 1 Mb chromosome does not associate more quickly than a 2.5 Mb chromosome, and that interstitial, single-copy sites can associate stably prior to nucleolar fusion. Analysis of two probes for the same pair of homologs revealed that by 4 h after karyogamy each chromosome examined was at least partially paired in all meiotic cells. In addition, these studies showed that chromatin condensation increases after pairing and that chromatin shows stable compaction at pachytene.

Chromatin↗

PubMed1999

Thermococcus siculi sp. nov., a novel hyperthermophilic archaeon isolated from a deep-sea hydrothermal vent at the Mid-Okinawa Trough.

A novel coccoid-shaped, hyperthermophilic, anaerobic archaeon, strain RG-20, was isolated from a deep-sea hydrothermal vent fluid sample taken at 1394-m depth at the Mid-Okinawa Trough (27 degrees 32.7'N, 126 degrees 58.5'E). Cells of this isolate occur singly or in pairs and are about 0.8 to 2 microm in diameter. Growth was observed at temperatures between 50 degrees and 93 degrees C, with an optimum at 85 degrees C. The pH range for growth is 5.0-9.0, with an optimum around 7.0. Strain RG-20 requires 1%-4% of NaCl for growth, and cell lysis occurs at concentrations below 1%. The newly isolated strain grows preferentially in the presence of elemental sulfur on proteinaceous substrates such as yeast extract, peptone, or tryptone, and no growth was observed on carbohydrates, carboxylic acids, alcohols, or lipids. This microorganism is resistant to streptomycin, chloramphenicol, ampicillin, and kanamycin at concentrations up to 150 microg/ ml, but is susceptible to rifampicin. Analysis of the hydrolyzed core lipids by thin-layer chromatography (TLC) revealed the presence of archaeol and caldarchaeol. The mol% G+C content of the DNA is 55.8. Partial sequencing of the 16S rDNA indicates that strain RG-20 belongs to the genus Thermococcus. Considering these data and on the basis of the results from DNA-DNA hybridization studies, we propose that this strain should be classified as a new species named Thermococcus siculi (si'cu.li. L. gen. n. siculi, of the deep-sea [siculum, deep-sea in literature of Ovid], referring to the location of the sample site, a deep-sea hydrothermal vent). The type strain is isolate RG-20 (DSM No. 12349).

DNA, Archaeal↗

PubMed1999

Novel archaeal phylotypes from an East African alkaline saltern.

DNA has been extracted on site from the brines of the final crystallizing pond of an alkaline saltern at Lake Magadi, Kenya. Amplification of 16S rRNA genes followed by cloning, sequencing, and phylogenetic analysis has revealed the presence of two distinct new archaeal lineages. The majority of cloned sequences showed greater than 95% identity to each other, but only 88%-90% similarity to any cultivated haloalkaliphilic Archaea, and form a distinct cluster within the known Haloarchaea. Two cloned genes showed close similarity to each other but only 76% similarity to any known archaeal sequence, and therefore represent a distinct phylotype only distantly related to the euryarchaeotal branch of the Archaea.

Africa, Eastern↗

PubMed1999

Predictors of safety belt use among crash-involved drivers and front seat passengers: adjusting for over-reporting.

Police-reported crash data are rarely used to investigate safety belt use and its predictors, even though these data have a number of advantages over data collected in roadside surveys. It has been widely recognized that motorists tend to over-report their safety belt use to police when mandatory belt use becomes law. In this paper, we use a logistic regression model that allows for misclassification errors in outcome variable to examine predictors of safety belt use among crash-involved drivers and front seat passengers. Our analysis shows significant associations between occupant characteristics, driving circumstances, and safety belt use. Alcohol involvement has the strongest negative association with safety belt use, but this association would be considerably underestimated without adjusting for the over-reporting of safety belt use in police-reported crash data. The adjusted belt use rate among front seat occupants with at least nonincapacitating injuries is about 81%, compared to 90% in police-reported crash data.

Accidents, Traffic↗