Biomedical subjects

Feng He

Publications and source records attributed to Feng He.

47 records · Page 3Linked to original sources

PubMed2003

Ponderomotive acceleration of electrons by a tightly focused intense laser beam.

Ponderomotive force driven acceleration of an electron at the focus of a high-intensity short-pulse laser is considered. Accounting for the asymmetry of acceleration and deceleration due to the evolution of the Gaussian laser beam waist, the energized electron is extracted from the laser pulse by the longitudinal ponderomotive force. It is shown that an electron's energy gain in the range of MeV can be realized for laser intensities above 10(19) W microm(2)/cm(2). Final energy gain as a function of the scattering angle and the electron's initial position has also been discussed.

Journal Article↗

PubMed2003

Synthesis, characteristics and luminescence properties of oligo(phenylenevinylene) dimers with a biphenyl linkage center.

Building a new structual oligo(phenylenevinylene) by linking trimeric phenylenvinylene (TPV) through the phenylphenyl bond of a central phenylene ring was reported. The resultant TPV dimers exhibit weak intermolecular interactions and intense blue photoluminescence in the solid state as well as high phase transition temperatures up to 250 degrees C. Organic light-emitting devices (OLEDs) based on these materials display blue emission with low turn-on voltage (about 3 V), maximum luminance approaching 2000 cd m(-2) and efficiency up to 1.6 cd A(-1).

Journal Article↗

PubMed2003

Profiling of genes expressed by PTEN haploinsufficient neural precursor cells.

PTEN is a lipid phosphatase, and PTEN mutations are associated with gliomas, macrocephaly, and mental deficiencies. We have used PTEN +/- and PTEN +/+ mice to prepare subventricular zone (SVZ) precursor cells. Using DNA microarrays, we compared the expression profiles of PTEN +/+ and PTEN +/- cells and identified 91 differentially expressed genes in PTEN +/- precursor cells. Many of the PTEN-regulated genes are involved with signaling, cytoskeleton, extracellular matrix, metabolism, and transcription factors. Some of these changes are likely mediated by the transcription factor, HIF-1. We confirmed a subset of these changes by real-time PCR. In addition, we examined protein levels for two of the PTEN-up-regulated genes, vascular endothelial growth factor (VEGF) and doublecortin (DCX). PTEN haploinsufficiency increases immunostaining for VEGF for both cultured precursor cells and sections of the SVZ. PTEN haploinsufficiency shifted most of the DCX-positive cells from the SVZ to the olfactory bulb. These observations indicate that even a small decrease in PTEN levels results in substantial changes in gene expression and precursor cell function.

Animals↗

PubMed2003

Genome-wide analysis of mRNAs regulated by the nonsense-mediated and 5' to 3' mRNA decay pathways in yeast.

Transcripts regulated by the yeast nonsense-mediated and 5' to 3' mRNA decay pathways were identified by expression profiling of wild-type, upf1Delta, nmd2Delta, upf3Delta, dcp1Delta, and xrn1Delta cells. This analysis revealed that inactivation of Upf1p, Nmd2p, or Upf3p has identical effects on global RNA accumulation; inactivation of Dcp1p or Xrn1p exhibits both common and unique effects on global RNA accumulation but causes upregulation of only a small fraction of transcripts; and the majority of transcripts upregulated in upf/nmd strains are also upregulated to similar extents in dcp1Delta and xrn1Delta strains. Our results define the core transcripts regulated by NMD, identify several novel structural classes of NMD substrates, demonstrate that nonsense-containing mRNAs are primarily degraded by the 5' to 3' decay pathway even in the absence of functional NMD, and indicate that 3' to 5' decay, not 5' to 3' decay, may be the major mRNA decay activity in yeast cells.

Cluster Analysis↗

PubMed2003

Nonsense-containing mRNAs that accumulate in the absence of a functional nonsense-mediated mRNA decay pathway are destabilized rapidly upon its restitution.

Nonsense-mediated mRNA decay (NMD) is a conserved proofreading mechanism that protects eukaryotic cells from the potentially deleterious effects of truncated proteins. Studies of Saccharomyces cerevisiae imply that NMD is a predominantly cytoplasmic decay pathway, while studies of mammalian systems suggest that decay of most substrate mRNAs may occur while they are still associated with the nucleus, possibly during a round of translation that occurs during their export to the cytoplasm. Complete entry of the latter mRNAs into the cytoplasm appears to render them immune to further NMD; i.e., they escape further susceptibility to this decay pathway. To determine if yeast cytoplasmic nonsense-containing mRNAs that evade decay are subsequently immune to NMD, we examined the consequences of placing each of the three UPF/NMD genes under the control of a galactose-inducible promoter. The decay kinetics of ADE2 and PGK1 nonsense-containing mRNAs were then analyzed when expression of UPF1, NMD2, or UPF3 was either repressed or subsequently induced. Results from these experiments demonstrated that activation of NMD caused rapid and immediate degradation of both substrate transcripts, with half-lives of both stable mRNA populations shortened to approximately 7 min. These findings make it unlikely that yeast nonsense-containing mRNAs can escape degradation by NMD and indicate that such mRNAs are available to this decay pathway at each round of translation.

Adaptor Proteins, Signal Transducing↗

PubMed2003

DNA polymerase beta gene expression: the promoter activator CREB-1 is upregulated in Chinese hamster ovary cells by DNA alkylating agent-induced stress.

The DNA alkylating agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) upregulates the level of the base excision DNA repair enzyme DNA polymerase beta (beta-pol) in several mammalian cell types. Previous studies suggested that beta-pol expression is upregulated via a transcriptional mechanism that requires: the specific cAMP response element (CRE) in the beta-pol core promoter; a phosphorylated form of CRE-binding protein-1 (CREB-1); and cellular protein kinase A activity. A large family of CRE-binding proteins, ie., the ATF/CREB factors, has been identified in various cell types. This study further examines the role of CRE-binding proteins in regulating beta-pol expression through study of Chinese hamster ovary (CHO) cells. In CHO cell nuclear extract, CREB-1 and ATF-1 are the predominant CRE-binding protein family members recognizing the CRE in the beta-pol core promoter. The concentration of CREB-1 increases strongly in CHO cells after exposure to MNNG. In contrast, the level of ATF-1 does not change after MNNG treatment. Recombinant expression of CREB-1 in CHO cells is sufficient to increase expression of the endogenous beta-pol gene, even in the absence of MNNG exposure. These results indicate that beta-pol gene expression in CHO cells can be upregulated by CREB-1 and that the activation of beta-pol gene expression in response to DNA alkylating agent exposure involves a strong increase in the level of CREB-1.

Activating Transcription Factor 1↗

PubMed2003

Photochemically enhanced degradation of phenol using heterogeneous Fenton-type catalysts.

The degradation of phenol was carried out using heterogeneous Fenton-type catalysts in the presence of H2O2 and UV. Catalysts were prepared by exchanging and immobilizing Fe2+ in zeolite 13X, silica gel or Al2O3. The concentration of phenol solution was 100 mg/L. The amount of H2O2 added was the stoichiometric amount of H2O2 required for the total oxidation of phenol. Under the irradiation of medium pressure light (300 W) phenol was mineralized within 1 h in the presence of Fe2+/zeolite 13X. The COD removal rate was enhanced in the presence of Fe2+/zeolite 13X compared to that of Fe2+/silica gel or Fe2+/Al2O3. Analogous homogenous photo-Fenton reaction with equivalent Fe2+ was also carried out to evaluate the catalysis efficiency of Fe2+/zeolite 13X. Results showed that the COD removal rate was near to that of homogeneous Fenton, while heterogeneous Fe2+/zeolite 13X catalyst could be recycled.

Catalysis↗

PubMed2003

[Effects of rehabilitation of submerged macrophytes on nutrient level of a eutrophic lake].

The effects of rehabilitation of submerged aquatic vegetation on nutrient level of eutrophic waters were investigated by using large-scale enclosure system installed in a hyper-eutrophicated lake, Lake Donghu of Wuhan. The concentrations of total nitrogen (TN) and total phosphorus (TP) of the enclosures with artificially recovered submerged macrophytes were significantly lower than those of the macrophyte-free control enclosure and the lake water, and the TP of macrophyte enclosure was found to be around 0.1 mg.L-1 and relatively stable. The concentration of ammonia and nitrite of the macrophyte enclosures were lower than those of the control and the lake water. However, the nitrate concentrations did not differ among the various water bodies. It was demonstrated that re-establishment of submerged macrophytes could efficiently reduce the nutrient level and thus control the overgrowth of the undesirable algae and improve water quality in the eutrophic lakes.

Ecosystem↗

PubMed2002

Point mutants of EHEC intimin that diminish Tir recognition and actin pedestal formation highlight a putative Tir binding pocket.

Attachment to host cells by enterohaemorrhagic Escherichia coli (EHEC) is associated with the formation of a highly organized cytoskeletal structure containing filamentous actin, termed an attaching and effacing (AE) lesion. Intimin, an outer membrane protein of EHEC, is required for the formation of AE lesions, as is Tir, a bacterial protein that is translocated into the host cell to function as a receptor for intimin. We established a yeast two-hybrid assay for intimin-Tir interaction and, after random mutagenesis, isolated 24 point mutants in intimin, which disrupted Tir recognition in this system. Analysis of 11 point mutants revealed a correlation between recognition of recombinant Tir and the ability to trigger AE lesions. Many of the mutations fell within a 50-residue region near the C-terminus of intimin. Alanine-scanning mutagenesis of this region revealed four residues (Ser890, Thr909, Asn916 and Asn927) that are critical for Tir recognition. Mapping the sequences of EHEC intimin and Tir onto the crystal structure of the intimin-Tir complex of enteropathogenic E. coli predicts that each of these four intimin residues lies at the intimin-Tir interface and contributes to a pocket that interacts with Ile298 of EHEC Tir. Thus, this genetic approach to intimin function both identified residues critical for Tir binding and demonstrated a correlation between the ability to bind Tir and the ability to trigger actin focusing.

Actins↗

PubMed2002

[Design and purification performance of vertical flow constructed wetland].

The technical design of small-scale plots (SSPs) of constructed wetland (CW) was described along with details of some associated wastewater purification effects in winter. Plots were comprised of two chambers. One chamber induced downward-flow, while the other created upward-flow. During Oct. 1997-Jan. 1998, the average plot removal rates for CODCr, BOD5 and total suspended solids were 53.6%, 78.7% and 80.2%, respectively. Reductions of bacteria, total coliforms (TC), fecal coliforms (FC) and algae were 99.4%, 85.9%, 89.7% and 97.7%, respectively. The mean removal rates of Kjeldahl nitrogen (KN), ammonium (NH4(+)-N) and total phosphorus (TP) were 39.2%, 16.5% and 25.8%. The treatment effects were not significantly different from each other. Concentrations of nitrate (NO3(-)-N) in effluents were higher than those of the influent, and nitrate concentrations in the effluents of plant-systems were higher than those of the control. This indicated that presence of macrophytes enhanced nitrification in the CW. The downward followed by upward flow CW performed better in removing contaminants and microorganisms from polluted surface water. It is an improved technology to purify water quality and rehabilitation of aquatic ecosystems.

Ecosystem↗

PubMed2002

[Application of the reaction theory to flow pattern on the integrated vertical flow constructed wetland].

This study was conducted to determine the flow pattern of the integrated vertical flow constructed wetland (IVCW) by using the reaction theory. The retention time distribution (RTD), obtained by tracer experiment, showed the retention time was between 19 and 35 h under 200-800 mm/d hydraulic loading rate, and the actual flow pattern was between the ideal plug flow and continuous stirred flow based on the characteristic value of the RTD. Furthermore, the dispersed flow model was found adequate in simulating the actual flow pattern of the IVCW and the Peclect number was determined between 11 and 19. Comparison the planted and unplanted IVCW, the plant root was found favorable for the flow pattern to approximate the ideal plug flow.

Waste Disposal, Fluid↗