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W Niu

Publications and source records attributed to W Niu.

33 records · Page 2Linked to original sources
PubMed1998

Mutational analysis of a transcriptional activation region of the VP16 protein of herpes simplex virus.

The VP16 protein of herpes simplex virus is a potent transcriptional activator of the viral immediate early genes. The transcriptional activation region of VP16 can be divided into two functional subregions, here designated VP16N (comprising amino acids 413-456) and VP16C (amino acids 450-490). Assays of VP16C mutants resulting from both random and alanine-scanning mutagenesis indicated that the sidechains of three phenylalanines (at positions 473, 475 and 479) and one acidic residue (glutamate 476) are important for transcriptional activation. Aromatic and bulky hydrophobic amino acids were effective substitutes for each of the three Phe residues, whereas replacement with smaller or polar amino acids resulted in loss of transcriptional function. In contrast, many changes were tolerated for Glu476, including bulky hydrophobic and basic amino acids, indicating that the negative charge at this position contributes little to the function of this subregion. Similar relative activities for most of the mutants were observed in yeast and in mammalian cells, indicating that the structural requirements for this activation region are comparable in these two species. These results reinforce the hypothesis that bulky hydrophobic residues, not acidic residues, are most critical for the activity of this 'acidic' transcriptional activation region.

Amino Acid Sequence↗
PubMed1998

A study on microleakage after resin filling of Class V cavities prepared by Er:YAG laser.

OBJECTIVE: The aims of this study were to investigate microleakage after composite resin filling to class V cavities prepared by Er:YAG laser and to compare the results with those obtained by a conventional method using an air turbine in vitro. SUMMARY BACKGROUND DATA: There has been no report of the microleakage study on class V cavities prepared by Er:YAG laser. METHODS: Forty-eight human extracted single root teeth were used in this study. Teeth were divided into three groups of sixteen each and class V cavities of the same size were prepared by Er:YAG laser for two groups and by air turbine for one group (control). For one group prepared by Er:YAG laser and the control group, the teeth were treated with 30% phosphoric acid. After the cavities were filled with the composite resin, the teeth except the areas of cavities and margins were covered by nail varnish and dye penetration was performed under the 0.6% Rhodamine B at 36 degrees C for 48 hrs. The teeth were sectioned at a thickness of 2 mm transversally and the slices were evaluated by stereoscopy and scanning electron microscopy (SEM). RESULTS: Microleakage at the cavity margins was observed in all three groups using the dye penetration method, but there was no significant difference among the three groups. SEM results showed similar results with the dye penetration method. CONCLUSION: These results suggest that microleakage at the cavities prepared by Er:YAG laser is at the same level as for prepared by air turbine using dye penetration and SEM methods.

Composite Resins↗
PubMed1998

Overexpression of insulin-like growth factor-binding protein-4 (IGFBP-4) in smooth muscle cells of transgenic mice through a smooth muscle alpha-actin-IGFBP-4 fusion gene induces smooth muscle hypoplasia.

Insulin-like growth factor I (IGF-I) has been postulated to function as a smooth muscle cell (SMC) mitogen and to play a role in the pathogenesis of bladder hypertrophy, estrogen-induced uterine growth, and restenosis after arterial angioplasty. IGF-binding protein-4 (IGFBP-4) inhibits IGF-I action in vitro and is the most abundant IGFBP in the rodent arterial wall. To explore the function of this binding protein in vivo, transgenic mouse lines were developed harboring fusion genes consisting of a rat IGFBP-4 complementary DNA cloned downstream of either a -724 bp fragment of the mouse smooth muscle alpha-actin 5'-flanking region (SMP2-BP-4) or -1074 bp, 63 bp of 5'-untranslated region, and 2.5 kb of intron 1 of smooth muscle alpha-actin (SMP8-BP-4). SMP2-BP-4 mice expressed low levels of the exogenous IGFBP-4 messenger RNA (mRNA), which was not specifically targeted to SMC-rich tissue environments, and were therefore not analyzed further. Six SMP8-BP-4 transgenic lines derived from separate founders were characterized. Mating of hemizygous SMP8-BP-4 mice with controls produced about 50% transgenic offspring, with equal sex distribution. Expression of IGFBP-4 mRNA in nontransgenic littermates was maximal in liver and kidney. By contrast, transgenic IGFBP-4 mRNA expression, distinguished because of a smaller transcript size, was confined to SMC-containing tissues, with the following hierarchy: bladder > aorta > stomach = uterus. There was no transgene expression in skeletal muscle, brain, or cardiac myocytes. The abundance of IGFBP-4 measured by Western ligand blotting or by immunoblotting, was 8- to 10-fold higher in aorta and bladder of SMP8-BP-4 mice than in their nontransgenic littermates, with no change in plasma IGFBP-4 levels. Transgenic mice exhibited a significant reduction in wet weight of SMC-rich tissues, including bladder, intestine, aorta, uterus, and stomach, with no change in total body or carcass weight. In situ hybridization showed that transgene expression was targeted exclusively to the muscular layers of the arteries, veins, bladder, ureter, stomach, intestine, and uterus. Overexpression of IGFBP-4 was associated with SMC hypoplasia, a reciprocal phenotype to that of transgenic mice overexpressing IGF-I under control of the same promoter (SMP8-IGF-I). Double transgenic mice derived from mating SMP8-BP-4 with SMP8-IGF-I animals showed a modest decrease in wet weight at selected SMC tissues. Although we cannot exclude that the effects of IGFBP-4 may be IGF independent, these data suggest that IGFBP-4 is a functional antagonist of IGF-I action on SMC in vivo.

Actins↗
PubMed1997

Targeted overexpression of IGF-I evokes distinct patterns of organ remodeling in smooth muscle cell tissue beds of transgenic mice.

Smooth muscle cells (SMC) of the vascular wall, bladder, myometrium, and gastrointestinal and respiratory tracts retain the ability to proliferate postnatally, which enables adaptive responses to injury, hormonal, or mechanical stimulation. SMC growth is regulated by a number of mesenchymal growth factors, including insulin-like growth factor I (IGF-I). To explore the function of IGF-I on SMC in vivo, the mouse SMC alpha-actin promoter fragment SMP8 (-1074 bp, 63 bp of 5'UT and 2.5 kb of intron 1) was cloned upstream of rat IGF-I cDNA, and the fusion gene microinjected to fertilized eggs of the FVB-N mouse strain. Mating of hemizygous mice with controls produced about 50% transgenic offspring, with equal sex distribution. Transgenic IGF-I mRNA expression was confined to SMC-containing tissues, with the following hierarchy: bladder > stomach > aorta = uterus > intestine. There was no transgene expression in skeletal muscle, heart, or liver. Radioimmunoassayable IGF-I content was increased by 3.5- to 4-fold in aorta, and by almost 10-fold in bladder of transgenic mice at 5 and 10 wk, with no change in plasma IGF-I levels. Wet weight of bladder, stomach, intestine, uterus, and aorta was selectively increased, with no change in total body or carcass weight of transgenic animals. In situ hybridization showed that transgene expression was exquisitely targeted to the smooth muscle layers of the arteries, veins, bladder, ureter, stomach, intestine, and uterus. Paracrine overproduction of IGF-I resulted in hyperplasia of the muscular layers of these tissues, manifesting in remarkably different phenotypes in the various SMC beds. Whereas the muscular layer of the bladder and stomach exhibited a concentric thickening, the SMC of the intestine and uterus grew in a longitudinal fashion, resulting in a marked lengthening of the small bowel and of the uterine horns. This report describes the first successful targeting of expression of any functional protein capable of modifying the phenotype of SMC in transgenic mice. IGF-I stimulates SMC hyperplasia, leading to distinct patterns of organ remodeling in the different tissue environments.

Animals↗
PubMed1997

AOTF microscope for imaging with increased speed and spectral versatility.

We have developed a new fluorescence microscope that addresses the spectral and speed limitations of current light microscopy instrumentation. In the present device, interference and neutral density filters normally used for fluorescence excitation and detection are replaced by acousto-optic tunable filters (AOTFs). Improvements are described, including the use of a dispersing prism in conjunction with the imaging AOTF and an oblique-illumination excitation scheme, which together enable the AOTF microscope to produce images comparable to those obtained with conventional fluorescence instruments. The superior speed and spectral versatility of the AOTF microscope are demonstrated by a ratio image pair acquired in 3.5 ms and a micro-spectral absorbance measurement of hemoglobin through a cranial window in a living mouse.

3T3 Cells↗
PubMed1997

Near-simultaneous hemoglobin saturation and oxygen tension maps in mouse brain using an AOTF microscope.

A newly developed microscope using acousto-optic tunable filters (AOTFs) was used to generate in vivo hemoglobin saturation (SO2) and oxygen tension (PO2) maps in the cerebral cortex of mice. SO2 maps were generated from the spectral analysis of reflected absorbance images collected at different wavelengths, and PO2 maps were generated from the phosphorescence lifetimes of an injected palladium-porphyrin compound using a frequency-domain measurement. As the inspiratory O2 was stepped from hypoxia (10% O2), through normoxia (21% O2), to hyperoxia (60% O2), measured SO2 and PO2 levels rose accordingly and predictably throughout. A plot of SO2 versus PO2 in different arterial and venous regions of the pial vessels conformed to the sigmoidal shape of the oxygen-hemoglobin dissociation curve, providing further validation of the two mapping procedures. The study demonstrates the versatility of the AOTF microscope for in vivo physiologic investigation, allowing for the generation of nearly simultaneous SO2 and PO2 maps in the cerebral cortex, and the frequency-domain detection of phosphorescence lifetimes. This class of study opens up exciting new possibilities for investigating the dynamics of hemoglobin and O2 binding during functional activation of neuronal tissues.

Acoustics↗
PubMed1997

Direct effects of somatostatin analog octreotide on insulin-like growth factor-I in the arterial wall.

Local vascular expression and action of insulin-like growth factor-I (IGF-I) appear to be important in the biologic events that follow arterial wall injury. Octreotide, a long-acting somatostatin analog, is a potent inhibitor of the growth hormone/IGF-I axis. We examined the effects of octreotide on the vascular IGF-I and IGF-binding proteins (IGFBP), gene regulation, smooth muscle cell proliferation, and neointimal thickening after arterial wall injury. Treatment with octreotide selectively decreased IGF-I mRNA expression in normal rat arteries by 70% and prevented the induction of the IGF-I gene after balloon injury. Because up-regulation of platelet-derived growth factor-A gene was not affected, and because there was no change in plasma growth hormone, IGF-I, and glucagon levels, it appears that this effect is selective and mediated locally. Of the IGFBP, IGFBP-4 was modestly up-regulated after balloon injury, whereas treatment with octreotide had no effect on IGFBP-4 expression. The inhibitory effects of octreotide on vascular IGF-I were associated with a decrease in the number of proliferating cell nuclear antigen-positive cells and an up to 90% reduction in neointimal thickening after balloon injury in a dose-dependent fashion.

Angioplasty, Balloon↗
PubMed1996

Transcription activation at class II CAP-dependent promoters: two interactions between CAP and RNA polymerase.

At Class II catabolite activator protein (CAP)-dependent promoters, CAP activates transcription from a DNA site overlapping the DNA site for RNA polymerase. We show that transcription activation at Class II CAP-dependent promoters requires not only the previously characterized interaction between an activating region of CAP and the RNA polymerase alpha subunit C-terminal domain, but also an interaction between a second, promoter-class-specific activating region of CAP and the RNA polymerase alpha subunit N-terminal domain. We further show that the two interactions affect different steps in transcription initiation. Transcription activation at Class II CAP-dependent promoters provides a paradigm for understanding how an activator can make multiple interactions with the transcription machinery, each interaction being responsible for a specific mechanistic consequence.

Amino Acids↗
PubMed1995

Effects of long-term acclimatization in lowlanders migrating to high altitude: comparison with high altitude residents.

The physiological response to submaximal and maximal exercise was assessed in lowlanders and Tibetans at low (500 m above sea level) and high altitude (HA, 3,680 m). The times spent at HA by the lowland migrators was 8 days (n = 60), 7 months (n = 60, same group), 15 months (n = 29) and 27 months (n = 29). After the 15-month stay at HA, the maximal oxygen uptake (VO2max) and maximal heart rate of the lowland migrators almost reached those of the HA native residents (Tibetans, n = 57), but their total work capacity and the gross efficiency (eta) of mechanical work remained lower than those of the Tibetans. The rate of VO2max achieved at 90 W by the Tibetans was lower than that of the lowland migrators. It was concluded that, at HA, the lowlanders regained much of the aerobic capacity which they had lost initially. However, they did not attain the same gross mechanical efficiency as the Tibetans, who seemed to be at an advantage in respect of work at HA.

Acclimatization↗
PubMed1994

Characterization of the activating region of Escherichia coli catabolite gene activator protein (CAP). I. Saturation and alanine-scanning mutagenesis.

It has been proposed that the surface loop consisting of amino acid residues 152 to 166 of the catabolite gene activator protein (CAP) of Escherichia coli makes direct protein-protein contact with RNA polymerase at the lac promoter. In this work, we have used targeted saturation mutagenesis of codons 152 to 166 of the gene encoding CAP, followed by a screen, to isolate more than 200 independent mutants of CAP defective in transcription activation but not defective in DNA binding. All isolated single-substitution mutants map to just eight amino acid residues; 156, 157, 158, 159, 160, 162, 163 and 164. We propose that these residues define the full extent of the epitope on CAP for the proposed CAP-RNA polymerase interaction. In addition, we have constructed alanine substitutions at each position from residue 152 to 166 of CAP, and we have analyzed the effects on transcription activation at the lac promoter and on DNA binding. Alanine substitution of Thr158 results in an approximately eightfold specific defect in transcription activation. In contrast, alanine substitution of no other residue tested results in a more than twofold specific defect in transcription activation. We conclude that, for Thr158, side-chain atoms beyond C beta are essential for transcription activation at the lac promoter, and we propose that Thr158 OH7 gamma makes direct contact with RNA polymerase in the ternary complex of lac promoter, CAP and RNA polymerase. We conclude further that for no residue other than Thr158 are side-chain atoms beyond C beta essential for transcription activation at the lac promoter.

Alanine↗
PubMed1993

A study of enzymohistochemistry of cerebral cortical injury.

Morphologic changes and quantitative determination by enzymohistochemistry were studied during various survival times after cortical injury in 60 rats. It was found that acid phosphatase (ACP) showed regular changes with various survival times after cortical injury. The ACP content decreased from 30 min to 6 h, and began to increase after 6 h; the ACP content in the region around injury decreased over the period of 5 days to 3 weeks after; the ACP content in the injured region (region around injury and control region of injury) decreased in a linear fashion with the time. The linear correlation was very marked; one may accurately estimate the survival time with injury by the regression equation given.

Acid Phosphatase↗
PubMedDate not supplied

Non-invasive image acquisition and advanced processing in optical bioimaging.

Light is a most versatile tool for investigating biological systems and phenomena; the range, non-destructiveness, spatial discrimination and speed of optical imaging are all important for investigating structure and function at the cellular, tissue or even whole organism level. In live biological imaging, where the technological requirements are heightened, other features of light, such as coherence and wavelength, are used to generate the additional contrast and resolution needed. We report here recent improvements in our ability to image biological specimens optically, focusing on (a) spectral resolution and the related image processing issues, and (b) tomographic three-dimensional fluorescence imaging in vivo.

Fluorescence↗