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Biomedical subjects

L Gan

Publications and source records attributed to L Gan.

At least 19 recordsLinked to original sources
PubMed2006

Cloning, chromosomal localization and expression patterns of porcine Kruppel-like factors 4, -5, -7 and the early growth response factor 2.

Kruppel-like factors (KLF) and the early growth response factor 2 (EGR2) are important zinc finger transcription factors in vertebrates. We have cloned the full length coding sequence (CDS) of porcine KLF5, KLF7 and EGR2, which are 1374, 909 and 1416 bp, respectively. KLF4, KLF5 and EGR2 were then chromosomally mapped to porcine 1q28-29, 11q13-14 and 14q23-25, respectively. Moreover, the tissue expression patterns of KLF4, KLF5, KLF7 and EGR2 imply their probable roles in specific tissues. This is the first report of the basic study of these zinc finger transcription factors in pigs; this information will be helpful for future functional studies.

Animals↗
PubMed2006

Search for Theta++ pentaquarks in the exclusive reaction gammap-->K+K-p.

The reaction gammap --> pK+K- was studied at Jefferson Lab with photon energies from 1.8 to 3.8 GeV using a tagged photon beam. The goal was to search for a Theta++ pentaquark, a narrow, doubly charged baryon state having strangeness S=+1 and isospin I=1, in the pK+ invariant mass spectrum. No statistically significant evidence of a Theta++ was found. Upper limits on the total and differential cross section for the reaction gammap --> K-Theta++ were obtained in the mass range from 1.5 to 2.0 GeV/c2, with an upper limit for a narrow resonance with a mass M(Theta++) = 1.54 GeV/c2 of about 0.15 nb, 95% C.L.. This result places a stringent upper limit on the Theta++ width Gamma(Theta++) <0.1 MeV/c2.

Journal Article↗
PubMed2006

Search for the Theta+ pentaquark in the reaction gammad --> pK-K+n.

A search for the Theta+ in the reaction gammad --> pK-K+n was completed using the CLAS detector at Jefferson Lab. A study of the same reaction, published earlier, reported the observation of a narrow Theta+ resonance. The present experiment, with more than 30 times the integrated luminosity of our earlier measurement, does not show any evidence for a narrow pentaquark resonance. The angle-integrated upper limit on Theta+ production in the mass range of 1.52-1.56 GeV/c2 for the gammad --> pK-Theta+ reaction is 0.3 nb (95% C.L.). This upper limit depends on assumptions made for the mass and angular distribution of Theta+ production. Using Lambda(1520) production as an empirical measure of rescattering in the deuteron, the cross section upper limit for the elementary gamman --> K-Theta+ reaction is estimated to be a factor of 10 higher, i.e., approximately 3 nb (95% C.L.).

Journal Article↗
PubMed2006

Quantization of 2D hole gas in conductive hydrogenated diamond surfaces observed by electron field emission.

Discrete jumps are observed in the emitted current density (J) versus extraction electric field (E) curves in electron field emission measurements from a conductive, hydrogen-terminated air-exposed diamond surface. These jumps are well reproduced by computations based on the assumption that a 2D nanoscale quantum system with discrete energy levels exists in the diamond near-surface layer. The present results confirm the formation of well-defined quantum states of holes in the 2D surface layer present on hydrogenated air-exposed diamond surfaces.

Journal Article↗
PubMed2006

Search for Theta+ (1540) Pentaquark in High-Statistics Measurement of gammap-->K0K+n at CLAS.

The exclusive reaction gammap-->K0K+n was studied in the photon energy range between 1.6 and 3.8 GeV searching for evidence of the exotic baryon Theta+ (1540)-->nK+. The decay to nK+requires the assignment of strangeness S=+1 to any observed resonance. Data were collected with the CLAS detector at the Thomas Jefferson National Accelerator Facility corresponding to an integrated luminosity of 70 pb-1. No evidence for the Theta+ pentaquark was found. Upper limits were set on the production cross section as function of center-of-mass angle and nK+ mass. The 95% C.L. upper limit on the total cross section for a narrow resonance at 1540 MeV was found to be 0.8 nb.

Journal Article↗
PubMed2006

Cloning, chromosome mapping and expression characteristics of porcine ANGPTL3 and -4.

Angiopoietin-like protein 3 and -4 (ANGPTL3 and -4) are two members of angiopoietin-like proteins (ANGPTLs), which have the signature structure of the angiopoietin family but cannot bind to the TIE2 receptor. It has been reported that they both affect lipid metabolism by inhibiting the activity of lipoprotein lipase (LPL). Here we report the cDNA cloning, chromosome mapping and expression analysis of ANGPTL3 and -4 in pigs. Sequence analysis shows that ANGPTL3 contains an open reading frame of 1,389 bp, which encodes 462 amino acids, and ANGPTL4 contains a coding region of 1,239 bp, which encodes 412 amino acids. Porcine ANGPTL3 deduced amino acid sequence shares 83% and 73.7% identity with human and mouse, respectively, and ANGPTL4 shares 79.4% and 77.7% amino acid identity with human and mouse, respectively. Porcine ANGPTL3 and -4 were mapped to the 6q31-->q35 and 2q21-->q24 region, respectively, by radiation hybrid mapping. Tissue distribution analysis indicated that porcine ANGPTL3 mRNA was exclusively expressed in liver, and porcine ANGPTL4 was ubiquitously expressed with the highest abundance in white adipose tissue. Furthermore, the mRNA level of ANGPTL3 and -4 in liver and the mRNA level of ANGPTL4 in white adipose tissue were significantly higher in genetically obese pigs than in their lean counterparts. This is the first report of molecular cloning and characterization of ANGPTL3 and -4 in pigs, which will be helpful for a better understanding of the role of ANGPTLs in lipid metabolism.

3' Untranslated Regions↗
PubMed2005

Cloning, expression and chromosome localization of porcine adiponectin and adiponectin receptors genes.

Adiponectin is a cytokine secreted specifically by adipocytes that has been proposed to enhance insulin sensitivity and prevent atherosclerosis. Adiponectin receptors (adipoR1 and adipoR2) are recently found in mice which act as receptors for globular and full-length adiponectin to mediate the fatty-acid oxidation and glucose uptake in muscle and liver. The primary goal of this study was to examine chromosome localization of porcine adiponectin and adiponectin receptors and the gene expression pattern in various tissues of pigs of the three genes. Radiation hybrid mapping demonstrated that porcine adiponectin, adipoR1 and adipoR2 were located to chromosome13q36-41, 10p11 and 5q25, in the regions that were syntenic to the homologs of human genes, respectively. Semi-quantitative RT-PCR showed that porcine adiponectin mRNA was specifically expressed in adipose tissue and porcine adipoR1 and adipoR2 mRNA were ubiquitously expressed in many tissues except brain. Comparison to adipoR2 mRNA which was highly expressed in liver, heart, kidney, adipose tissues and lung, adipoR1 mRNA was expressed at relatively high levels in porcine muscle, leukocytes and epididymis. Our data provide basic molecular information useful for the further investigation on the function of the three genes.

Adiponectin↗
PubMed2005

Cloning and characterization of porcine resistin gene.

Resistin is a member of resistin-like molecules (RELMs) and a hormone secreted from mature adipocytes in rodents and leukocytes in human. We now report the cloning and characterization of the full-length porcine resistin cDNA and gene. Sequence analysis indicated that the pig resistin cDNA sequence had an open reading frame of 330 bp encoding a 12 kDa protein of 109 amino acids. The deduced amino acid sequence showed 75.2% identity to the human resistin. The porcine resistin gene was composed of four exons and had exactly the same exon structure as the human resistin gene. The tissue distribution of porcine resistin mRNA was assessed by semi-quantitative RT-PCR. Resistin gene expression was the highest in porcine leukocytes and low in adipose tissue. Resistin protein could be detected in porcine serum by western blotting and it circulated in serum as dimers and trimers. We provided the first evidence that resistin was abundantly expressed in porcine leukocytes and had an expression pattern similar to that in human resistin mRNA and protein. This suggests that the pig may be a suitable animal model for studying the function of resistin in human insulin resistance.

Amino Acid Sequence↗
PubMed2004

Angular distributions for (3,4)(Lambda)H bound states in the (3,4)He(e,e(')K+) reaction.

The (3,4)(Lambda)H and (4)(Lambda)H hypernuclear bound states have been observed for the first time in kaon electroproduction on (3,4)He targets. The production cross sections have been determined at Q(2)=0.35 GeV2 and W=1.91 GeV. For either hypernucleus the nuclear form factor is determined by comparing the angular distribution of the (3,4)He(e,e(')K+)(3,4)(Lambda)H processes to the elementary cross section 1H(e,e K+)Lambda on the free proton, measured during the same experiment.

Journal Article↗
PubMed2004

Stage-specific expression of leukaemia inhibitory factor and its receptor in rabbit pre-implantation embryo and uterine epithelium during early pregnancy.

Leukaemia inhibitory factor (LIF) has been shown to play an important role in the development and implantation of blastocysts in mice. In the current study, the reverse transcription-polymerase chain reaction (RT-PCR) was employed to examine the expression patterns of LIF and its receptor (LIFR) genes in rabbit embryos during pre-implantation development, and the uterine expression of LIF and LIFR was also evaluated by Western blotting. Transcripts for LIFR were detected within morula and blastocyst-stage embryos, while the LIF mRNA was only found in blastocysts (from early to fully expanded blastocoel cavities), indicating that embryo-derived LIF can act in an autocrine manner on the process of blastocyst formation. The expression levels of LIF and LIFR in uterine epithelium were gradually increased during pre-implantation period and reached their highest levels on days 6.5 of pregnancy, just before the time of blastocyst implantation, suggest that paracrine LIF circuit should exist between the endometrium and the early embryos, which may be involved in the embryo-maternal dialogue and important for the blastocyst implantation. The data present here show the stage-specific and dynamic expression patterns of LIF and LIFR, both in embryos and endometrium, during early pregnancy in rabbits, which indicated that LIF might play an important role in the pre-implantation development and subsequent implantation of rabbit embryos.

Animals↗
PubMed2004

Increased expression of resistin and tumour necrosis factor-alpha in pig adipose tissue as well as effect of feeding treatment on resistin and cAMP pathway.

AIM: Resistin, a novel hormone, is expressed in mouse, rat and human adipose tissue. Its resistance to insulin is controversial. We hypothesized that resistin has the similar roles like those of tumour necrosis factor-alpha (TNF-alpha), a putative mediator of insulin resistance, and they are in common involved in regulating lipid metabolism in vivo. METHODS: We demonstrated TNF-alpha and resistin expression in different growth-stage adipose tissue of genetically lean and obese pigs using semiquantitative reverse transcriptase-polymerase chain reaction and Western blotting analysis. Moreover, we analysed the variations of resistin and some parameters associated with lipolysis pathway after body-weight reduction in feeding-restricted obese pigs. In addition, we localized resistin expression in the cell types from pig adipose tissue. RESULTS: Overall, the expression of TNF-alpha and resistin in obese pigs was statistically higher than their lean counterparts, although this difference in resistin mRNA expression tailed off with age. In individual pigs, their levels increased progressively with age and degree of obesity. After feeding restriction, resistin expression was gradually decreased. Simultaneously, feeding restriction also resulted in a significant decrease of serum triglyceride and plasma cAMP, free fatty acids and insulin as well as fat adenyl cyclase and cAMP. In addition, in isolated pig adipocytes, our data showed that resistin was localized not only to adipocytes but also to other unidentified stromal vascular cells. CONCLUSIONS: TNF-alpha and resistin are increased in obesity. Weight loss results in the decrease of resistin and lipolysis-associated parameters, suggesting the possible association between resistin and lipolysis pathway. Cell localization of resistin expression implies the possibility of other biological actions of resistin.

Adipose Tissue↗
PubMed2003

Measurements of GnE/GnM from the 2H(e-->,en-->)1H Reaction to Q2=1.45 (GeV/c)2.

We report new measurements of the ratio of the electric form factor to the magnetic form factor of the neutron, G(n)(E)/G(n)(M), obtained via recoil polarimetry from the quasielastic 2H(e-->,e(')n-->)1H reaction at Q2 values of 0.45, 1.13, and 1.45 (GeV/c)(2) with relative statistical uncertainties of 7.6% and 8.4% at the two higher Q2 points, which points have never been achieved in polarization measurements.

Journal Article↗
PubMed2003

An in vitro Flaviviridae replicase system capable of authentic RNA replication.

We have established an in vitro replication system for bovine viral diarrhea virus (BVDV), a surrogate for the closely-related hepatitis C virus. In an in vitro reaction, BVDV replication complexes synthesize vRNA and replicative form (RF) and replicative intermediate (RI) RNAs. Kinetic and heparin trapping experiments demonstrate the recycling of RF and RI products and the initiation of vRNA synthesis in this system. Consistent with this, quantitative hybridization reveals the asymmetric synthesis of positive and negative strand RNA products. These findings support the notion that RF serves as a template and RI as a precursor in the synthesis of vRNA. Furthermore, the antiviral activity of an NS5B inhibitor was similar in BVDV replicase and infectivity assays. Together, these results indicate that the in vitro activity of BVDV replicase complexes recapitulates RNA replication that occurs in infected cells, providing a system in which to study both mechanisms and inhibitors of Flaviviridae replication.

Animals↗
PubMed2003

High resolution spectroscopy of the 12Lambda B hypernucleus produced by the (e,e'K+) reaction.

High-energy, cw electron beams at new accelerator facilities allow electromagnetic production and precision study of hypernuclear structure, and we report here on the first experiment demonstrating the potential of the (e,e'K+) reaction for hypernuclear spectroscopy. This experiment is also the first to take advantage of the enhanced virtual photon flux available when electrons are scattered at approximately zero degrees. The observed energy resolution was found to be approximately 900 keV for the (12)(Lambda)B spectrum, and is substantially better than any previous hypernuclear experiment using magnetic spectrometers. The positions of the major excitations are found to be in agreement with a theoretical prediction and with a previous binding energy measurement, but additional structure is also observed in the core excited region, underlining the future promise of this technique.

Journal Article↗
PubMed2002

Specific interference with gene expression and gene function mediated by long dsRNA in neural cells.

Double-stranded (ds) RNA-induced sequence-specific interference with gene expression, RNA interference (RNAi), has been extensively used in invertebrates, allowing for efficient and high-throughput gene silencing and gene function analysis. In vertebrates, however, use of RNAi to study gene function has been limited due to non-specific effects induced by double-stranded RNA (dsRNA)-dependent protein kinase and interferon activation. dsRNA-induced specific inhibition of vertebrate gene expression has only been shown in embryonic and non-differentiated mammalian cells. In this report, we demonstrate dsRNA-induced specific interference of gene expression and gene function in partially as well as fully differentiated mouse neuroblastoma cells. Specific silencing was observed in the expression of an integrated transgene coding for green fluorescent protein and a variety of endogenous genes. Moreover, we show that RNAi-mediated inhibition of poly (ADP-ribose) polymerase (PARP) expression induced cellular resistance to oxygen-glucose deprivation, consistent with the role of PARP in ischemia-induced brain damage. Our results indicate that RNAi can be used as a powerful tool to study gene function in neural cells.

Animals↗