Biomedical subjects

X Pan

Publications and source records attributed to X Pan.

At least 55 records · Page 3Linked to original sources

PubMed2000

Non-iterative methods incorporating a priori source distribution and data information for suppression of image noise and artefacts in 3D SPECT.

Non-iterative methods have been developed for image reconstruction in 3D SPECT with uniform attenuation and distance-dependent spatial resolution. It was observed that these methods can, in general, be susceptible to data noise and other errors, yielding conspicuous image artefacts. In this work, we developed and evaluated a regularized inverse-filtering approach for effective suppression of noise and artefacts in 3D SPECT images without significantly compromising image resolution. The proposed approach allows the incorporation of a priori random image field and data information and can thus robustly control the degree of suppression of noise and artefacts in 3D SPECT images. Using computer simulations, we evaluated and compared quantitatively images reconstructed from data sets of various noise levels by the use of the proposed methods and the existing non-iterative methods. These numerical results clearly demonstrated that the proposed regularized inverse-filtering approach can effectively suppress image noise and artefacts that plague the existing non-iterative methods, thus yielding quantitatively more accurate 3D SPECT images. The proposed regularized inverse-filtering approach can also be generalized to other imaging modalities.

Algorithms↗

PubMed2000

Nucleus-vacuole junctions in Saccharomyces cerevisiae are formed through the direct interaction of Vac8p with Nvj1p.

Vac8p is a vacuolar membrane protein that is required for efficient vacuole inheritance and fusion, cytosol-to-vacuole targeting, and sporulation. By analogy to other armadillo domain proteins, including beta-catenin and importin alpha, we hypothesize that Vac8p docks various factors at the vacuole membrane. Two-hybrid and copurfication assays demonstrated that Vac8p does form complexes with multiple binding partners, including Apg13p, Vab2p, and Nvj1p. Here we describe the surprising role of Vac8p-Nvj1p complexes in the formation of nucleus-vacuole (NV) junctions. Nvj1p is an integral membrane protein of the nuclear envelope and interacts with Vac8p in the cytosol through its C-terminal 40-60 amino acids (aa). Nvj1p green fluorescent protein (GFP) concentrated in small patches or rafts at sites of close contact between the nucleus and one or more vacuoles. Previously, we showed that Vac8p-GFP concentrated in intervacuole rafts, where is it likely to facilitate vacuole-vacuole fusion, and in "orphan" rafts at the edges of vacuole clusters. Orphan rafts of Vac8p red-sifted GFP (YFP) colocalize at sites of NV junctions with Nvj1p blue-sifted GFP (CFP). GFP-tagged nuclear pore complexes (NPCs) were excluded from NV junctions. In vac8-Delta cells, Nvj1p-GFP generally failed to concentrate into rafts and, instead, encircled the nucleus. NV junctions were absent in both nvj1-Delta and vac8-Delta cells. Overexpression of Nvj1p caused the profound proliferation of NV junctions. We conclude that Vac8p and Nvj1p are necessary components of a novel interorganelle junction apparatus.

Cell Fractionation↗

PubMed2000

The G protein-coupled receptor gpr1 is a nutrient sensor that regulates pseudohyphal differentiation in Saccharomyces cerevisiae.

Pseudohyphal differentiation in the budding yeast Saccharomyces cerevisiae is induced in diploid cells in response to nitrogen starvation and abundant fermentable carbon source. Filamentous growth requires at least two signaling pathways: the pheromone responsive MAP kinase cascade and the Gpa2p-cAMP-PKA signaling pathway. Recent studies have established a physical and functional link between the Galpha protein Gpa2 and the G protein-coupled receptor homolog Gpr1. We report here that the Gpr1 receptor is required for filamentous and haploid invasive growth and regulates expression of the cell surface flocculin Flo11. Epistasis analysis supports a model in which the Gpr1 receptor regulates pseudohyphal growth via the Gpa2p-cAMP-PKA pathway and independently of both the MAP kinase cascade and the PKA related kinase Sch9. Genetic and physiological studies indicate that the Gpr1 receptor is activated by glucose and other structurally related sugars. Because expression of the GPR1 gene is known to be induced by nitrogen starvation, the Gpr1 receptor may serve as a dual sensor of abundant carbon source (sugar ligand) and nitrogen starvation. In summary, our studies reveal a novel G protein-coupled receptor senses nutrients and regulates the dimorphic transition to filamentous growth via a Galpha protein-cAMP-PKA signal transduction cascade.

Carbohydrate Metabolism↗

PubMed2000

Identification of human GATA-2 gene distal IS exon and its expression in hematopoietic stem cell fractions.

Transcription factor GATA-2 is essential for the proper function of hematopoietic stem cells and progenitors. Two first exons/promoters have been found in the mouse GATA-2 gene, and a distal IS promoter shows activity specific to hematopoietic progenitors and neural tissues. To ascertain whether the two-promoter system is also utilized in the human GATA-2 gene, we isolated and analyzed a P1 phage clone containing this gene. The nucleotide sequence of the human GATA-2 gene 5' flanking region was determined over 10 kbp, and a human IS exon was identified in the locus through sequence comparison analysis with that of the mouse GATA-2 IS exon. RNA blotting and reverse-transcribed PCR analyses identified a transcript that starts from the IS exon in human leukemia-derived cell lines. The IS-originated transcript was also identified in CD34-positive bone marrow and cord blood mononuclear cells, which are recognized as clinically important hematopoietic stem cell-enriched fractions. Phylogenic comparison of the human and mouse GATA-2 gene sequences revealed several regions in the locus that exhibit high sequence similarity. These results demonstrate that the GATA-2 gene regulatory machinery is conserved among vertebrates. The fact that the human IS promoter is active in the hematopoietic stem cell/progenitor fraction may be an important clue for the design of a vector system that can specifically express various genes in hematopoietic stem cells and progenitors.

Animals↗

PubMed2000

Consistency conditions and linear reconstruction methods in diffraction tomography.

Because an image can be reconstructed from knowledge of its Radon transform (RT), the task of reconstructing an image is tantamount to that of estimating its RT. Based upon the Fourier diffraction projection (FDP) theorem, from the statistical perspective of unbiased reduction of image variance, we previously proposed an infinite family of estimation methods for obtaining the RT from the scattered data in diffraction tomography (DT). In this work, using the FDP theorem, we define the diffraction Radon transform (DRT), which can be treated as the data function in DT. Subsequently, using strategies similar to those that analyze the consistency conditions on the exponential Radon transform in two-dimensional (2-D) single-photon emission computed tomography with uniform attenuation, we studied the consistency condition on the DRT and we show that there is a hierarchy of estimation methods that actually project the noisy data function onto its consistency space in different ways. In terms of a weighted inner product of the consistency and inconsistency parts of a noisy data function, we further demonstrate that a subset of the family of estimation methods can be interpreted as orthogonal projections onto the consistency space of the DRT. In particular, the statistically suboptimal estimation method in the family corresponds to an orthogonal projection associated with an ordinary inner product of the consistency and inconsistency parts of a noisy data function.

Algorithms↗

PubMed2000

Nonparametric regression sinogram smoothing using a roughness-penalized Poisson likelihood objective function.

We develop and investigate an approach to tomographic image reconstruction in which nonparametric regression using a roughness-penalized Poisson likelihood objective function is used to smooth each projection independently prior to reconstruction by unapodized filtered backprojection (FBP). As an added generalization, the roughness penalty is expressed in terms of a monotonic transform, known as the link function, of the projections. The approach is compared to shift-invariant projection filtering through the use of a Hanning window as well as to a related nonparametric regression approach that makes use of an objective function based on weighted least squares (WLS) rather than the Poisson likelihood. The approach is found to lead to improvements in resolution-noise tradeoffs over the Hanning filter as well as over the WLS approach. We also investigate the resolution and noise effects of three different link functions: the identity, square root, and logarithm links. The choice of link function is found to influence the resolution uniformity and isotropy properties of the reconstructed images. In particular, in the case of an idealized imaging system with intrinsically uniform and isotropic resolution, the choice of a square root link function yields the desirable outcome of essentially uniform and isotropic resolution in reconstructed images, with noise performance still superior to that of the Hanning filter as well as that of the WLS approach.

Algorithms↗

PubMed2000

Fast reconstruction with uniform noise properties in halfscan computed tomography.

The hybrid algorithms developed recently for the reconstruction of fan-beam images possess computational and noise properties superior to those of the fan-beam filtered backprojection (FFBP) algorithm. However, the hybrid algorithms cannot be applied directly to a halfscan fan-beam sinogram because they require knowledge of a fullscan fan-beam sinogram. In this work, we developed halfscan-hybrid algorithms for image reconstruction in halfscan computed tomography (CT). Numerical evaluation indicates that the proposed halfscan-hybrid algorithms are computationally more efficient than are the widely used halfscan-FFBP algorithms. Also, the results of quantitative studies demonstrated clearly that the noise levels in images reconstructed by use of the halfscan-hybrid algorithm are generally lower and spatially more uniform than are those in images reconstructed by use of the halfscan-FFBP algorithm. Such reduced and uniform image noise levels may be translated into improvement of the accuracy and precision of lesion detection and parameter estimation in noisy CT images without increasing the radiation dose to the patient. Therefore, the halfscan-hybrid algorithms may have significant implication for image reconstruction in conventional and helical CT.

Algorithms↗

PubMed2000

Sequence-based identification of Mycobacterium species using the MicroSeq 500 16S rDNA bacterial identification system.

We evaluated the MicroSeq 500 16S rDNA Bacterial Sequencing Kit (PE Applied Biosystems), a 500-bp sequence-based identification system, for its ability to identify clinical Mycobacterium isolates. The organism identity was determined by comparing the 16S rDNA sequence to the MicroSeq database, which consists primarily of type strain sequences. A total of 113 isolates (18 different species), previously recovered and identified by routine methods from two clinical laboratories, were analyzed by the MicroSeq method. Isolates with discordant results were analyzed by hsp65 gene sequence analysis and in some cases repeat phenotypic identification, AccuProbe rRNA hybridization (Gen-Probe, Inc., San Diego, Calif.), or high-performance liquid chromatography of mycolic acids. For 93 (82%) isolates, the MicroSeq identity was concordant with the previously reported identity. For 18 (16%) isolates, the original identification was discordant with the MicroSeq identification. Of the 18 discrepant isolates, 7 (six unique sequences) were originally misidentified by phenotypic analysis or the AccuProbe assay but were correctly identified by the MicroSeq assay. Of the 18 discrepant isolates, 11 (seven unique sequences) were unusual species that were difficult to identify by phenotypic methods and, in all but one case, by molecular methods. The remaining two isolates (2%) failed definitive phenotypic identification, but the MicroSeq assay was able to definitively identify one of these isolates. The MicroSeq identification system is an accurate and rapid method for the identification of Mycobacterium spp.

Bacterial Proteins↗

PubMed2000

Characterization of Mycobacterium tuberculosis isolates from patients in Houston, Texas, by spoligotyping.

Mycobacterium tuberculosis isolates (n = 1,429) from 1,283 patients collected as part of an ongoing population-based tuberculosis epidemiology study in Houston, Texas, were analyzed by spoligotyping and IS6110 profiling. The isolates were also assigned to one of three major genetic groups on the basis of nucleotide polymorphisms located at codons 463 and 95 in the genes (katG and gyrA) encoding catalase-peroxidase and the A subunit of DNA gyrase, respectively. A total of 225 spoligotypes were identified in the 1,429 isolates. There were 54 spoligotypes identified among 713 isolates (n = 623 patients) assigned to 73 IS6110 clusters. In addition, among 716 isolates (n = 660 patients) with unique IS6110 profiles, 200 spoligotypes were identified. No changes were observed either in the IS6110 profile or in the spoligotype for the 281 isolates collected sequentially from 133 patients. Five instances in which isolates with slightly different spoligotypes had the same IS6110 profile were identified, suggesting that in rare cases isolates with different spoligotypes can be clonally related. Spoligotypes correlated extremely well with major genetic group designations. Only three very similar spoligotypes were shared by isolates from genetic groups 2 and 3, and none was shared by group 1 and group 2 organisms or by group 1 and group 3 organisms. All organisms belonging to genetic groups 2 and 3 failed to hybridize with spacer probes 33 to 36. Taken together, the results support the existence of three distinct genetic groups of M. tuberculosis organisms and provide new information about the relationship between IS6110 profiles, spoligotypes, and major genetic groups of M. tuberculosis.

Bacterial Proteins↗

PubMed2000

Sok2 regulates yeast pseudohyphal differentiation via a transcription factor cascade that regulates cell-cell adhesion.

In response to nitrogen limitation, Saccharomyces cerevisiae undergoes a dimorphic transition to filamentous pseudohyphal growth. In previous studies, the transcription factor Sok2 was found to negatively regulate pseudohyphal differentiation. By genome array and Northern analysis, we found that genes encoding the transcription factors Phd1, Ash1, and Swi5 were all induced in sok2/sok2 hyperfilamentous mutants. In accord with previous studies of others, Swi5 was required for ASH1 expression. Phd1 and Ash1 regulated expression of the cell surface protein Flo11, which is required for filamentous growth, and were largely required for filamentation of sok2/sok2 mutant strains. These findings reveal that a complex transcription factor cascade regulates filamentation. These findings also reveal a novel dual role for the transcription factor Swi5 in regulating filamentous growth. Finally, these studies illustrate how mother-daughter cell adhesion can be accomplished by two distinct mechanisms: one involving Flo11 and the other involving regulation of the endochitinase Cts1 and the endoglucanase Egt2 by Swi5.

Cell Adhesion↗

PubMed2000

Signal transduction cascades regulating fungal development and virulence.

Cellular differentiation, mating, and filamentous growth are regulated in many fungi by environmental and nutritional signals. For example, in response to nitrogen limitation, diploid cells of the yeast Saccharomyces cerevisiae undergo a dimorphic transition to filamentous growth referred to as pseudohyphal differentiation. Yeast filamentous growth is regulated, in part, by two conserved signal transduction cascades: a mitogen-activated protein kinase cascade and a G-protein regulated cyclic AMP signaling pathway. Related signaling cascades play an analogous role in regulating mating and virulence in the plant fungal pathogen Ustilago maydis and the human fungal pathogens Cryptococcus neoformans and Candida albicans. We review here studies on the signaling cascades that regulate development of these and other fungi. This analysis illustrates both how the model yeast S. cerevisiae can serve as a paradigm for signaling in other organisms and also how studies in other fungi provide insights into conserved signaling pathways that operate in many divergent organisms.

Calcineurin↗

PubMed2000

Computationally efficient and statistically robust image reconstruction in three-dimensional diffraction tomography.

Diffraction tomography (DT) is an inversion scheme used to reconstruct the spatially variant refractive-index distribution of a scattering object. We developed computationally efficient algorithms for image reconstruction in three-dimensional (3D) DT. A unique and important aspect of these algorithms is that they involve only a series of two-dimensional reconstructions and thus greatly reduce the prohibitively large computational load required by conventional 3D reconstruction algorithms. We also investigated the noise characteristics of these algorithms and developed strategies that exploit the statistically complementary information inherent in the measured data to achieve a bias-free reduction of the reconstructed image variance. We performed numerical studies that corroborate our theoretical assertions.

Algorithms↗

PubMed2000

[The influence of epidermal growth factor, neurotensin on cytosolic calcium and membrane fluidity in carbon tetrachloride-injured primary cultured hepatocytes].

OBJECTIVE: To study the influence of epidermal growth factor (EGF), neurotensin (NT) on cytosolic calcium and membrane fluidity in carbon tetrachloride-injured primary cultured hepatocytes. METHODS: A micro-model of carbon tetrachloride -induced primary cultured hepatocytes injury was established. EGF and NT were added to the cells 1 h ahead of carbon tetrachloride given. Twenty-four hours later, cytosolic calcium and membrane fluidity in hepatocytes were detected with fluorescence probe of Fura-2/AM and 1, 6-dihenyl-1, 3, 5-hexatriene (DPH). RESULTS: EGF and NT could significantly antagonize the increase of cytosolic Ca(2+) and decrease of membrane fluidity in carbon tetrachloride-injured hepatocytes. CONCLUSION: EGF and NT have a function of maintaining membrane fluidity and steady-status of cytosolic calcium of hepatocytes.

Animals↗

PubMed2000

In vitro inhibition of rat monoamine oxidase by liquiritigenin and isoliquiritigenin isolated from Sinofranchetia chinensis.

AIM: To study the inhibition of liquiritigenin (1) and isoliquiritigenin (2) isolated from Sinofranchetia chinensis on rat monoamine oxidase A and B (MAO A and B). METHODS: Rat brain mitochondrial fraction, prepared by differential centrifugation, was utilized as a source of MAO activity. MAO activity was determined radiochemically with [14C]5-hydroxytryptamine (5-HT) and [14C]beta-phenylethylamine (beta-PEA) used as MAO A or B specific radiolabled substrates, respectively. The Ki and KI values were obtained from Lineweaver-Burk plot using linear regression analysis. RESULTS: Liquiritigenin and isoliquiritigenin were found to be inhibitory against both MAO A and B in a dose-dependent manner. IC50 (95% of confidence limits) of liquiritigenin and isoliquiritigenin were 32 (26-36) and 13.9 (12.8-15.6) mumol/L for the inhibition of MAO A, and 104.6 (89.0-118.9) and 47.2 (39.5-54.5) mumol/L for that of MAO B, respectively. Lineweaver-Burk transformation of the MAO A inhibition data indicated that the inhibition was non-competitive for both liquiritigenin and isoliquiritigenin whereas their inhibition of MAO B was of mixed type. Regarding MAO A inhibition, the Ki values of liquiritigenin and isoliquiritigenin were 31.5 mumol/L and 14.3 mumol/L, respectively. As to the inhibition of MAO B, the Ki and KI data for liquiritigenin were 164.7 and 15.2 mumol/L, and those for isoliquiritigenin were 62.2 and 9.3 mumol/L, respectively. CONCLUSION: Liquiritigenin and isoliquiritigen inhibited the activity of MAO A and B in rat brain mitochondria, and the latter was more active than the former.

Animals↗

PubMed2000

[Construction of adenovirus vector for human p27kip1 gene and its expression].

OBJECTIVE: To study the effects of exogenous p27kip1 gene on cell cycle and proliferation. METHODS: E1 substitutive adenovirus vector pAxlcw containing human p27kip1 cDNA (Cihp27kip1) under the transcriptional control of CMV promoter was constructed and then cotransfected with Ad5 adenovirus DNA-terminal peptide complex EcoT221-digested into 293 cells for preparing p27kip1 recombinant adenovirus Adhp27kip1. After infecting HeLa cells for 24 h, the exogenous p27kip1 protein expression in HeLa cells and its effects on cell cycle and proliferation were determined by Western blot, FACS and MTT assay. RESULTS: The titers of resultant recombinant adenoviruses was 1.7 x 10(9) pfu/ml. p27kip1 protein was over-expressed in HeLa cells infected with p27kip1 recombinant adenovirus for 24 h, resulting in blockage of cell cycle transition from G1 phase to S phase and inhibition of cell proliferation. CONCLUSION: p27kip1 recombinant adenoviruses prepared in this study can efficiently transfer p27kip1 gene into HeLa cells and over-express p27kip1 protein in the infected cells. Adhp27kip1 can be used as an agent for gene therapy.

Adenoviridae↗

PubMed2000

[Effect of nm23H1 on proliferation, tumor formation and metastasis of hepatocarcinoma].

OBJECTIVE: To study the effects of nm23H1 on in vitro proliferation, in vivo tumor formation and metastasis of hepatocarcinoma. METHODS: Vectors containing insert of either sense or antisense nm23H1 cDNA under the albumin enhancer/promoter for liver cell-specific expression were constructed. The expression vectors were transfected into hepatocarcinoma cell line SMMC-7721. Stable cell clones with maximum and minimum expression of nm23 were obtained. Cell growth was measured in vitro and metastasis was observed in vivo by injecting cells into nude mice, subcutaneously or under the spleen capsule. RESULTS: In vitro, cell clone expressing antisense nm23H1 grew faster than that expressing sense nm23H1. In nude mice, the subcutaneously inoculated tumor grew faster and more aggressively in mice bearing antisense nm23H1 transfected hepatoma. So did metastasis of the antisense nm23H1 transfected hepatoma under the spleen capsule. CONCLUSION: Apart from suppressing metastasis, nm23H1 significantly suppresses tumor cell proliferation in vitro and tumor growth in vivo.

Animals↗

PubMed2000

[A serological investigation of Legionella infection in eight-species of poultry and domestic animals in Sichuan province].

OBJECTIVE: To understand the prevalence rates of Legionella infection in poultries and domestic animals in Sichuan province. METHODS: Serological investigation of antibodies against Legionella pneumophila serogroups 1 - 14 and Legionella micdadei was carried out, using microagglutination test (MAT) in eight species of poultries and domestic animals. RESULTS: Infections with multiple serogroups were identified. However, each species had its own major serogroup with positive rates of different serogroups ranging from 0.83% to 59.18%. Positive rates of the poultry and domestic animals were accounted for 7.73% and 4.25% respectively. CONCLUSION: It was suggested that poultries and domestic animals were widely infected with Legionella. It is important to carry out epidemiological surveillance in these domestic animals, poultries and environment for a better control program of this disease.

Animals↗

PubMed2000

[The Ahmed glaucoma valve implantation for refractory glaucoma].

OBJECTIVE: To evaluate the efficacy of the Ahmed Glaucoma Valve implant in the treatment of refractory glaucoma. METHODS: 28 cases(29 eyes) of refractory glacucoma were treated by the Ahmed glaucoma Valve implant, including 10 cases (10 eyes) of neovascula glaucoma, 5 cases (6 eyes) of juvenile glaucoma and 13 cases (13 eyes) of other causes glaucoma. RESULTS: Post-operative follow-up time was 3-12 months. The intraocular pressure (IOP) was lowered from preoperative 40.9 +/- 7.32 mmHg (1 mmHg = 0.133 kPa) to postoperative 20.63 +/- 2.75 mmHg in Neovascular glaucoma; from preoperative 41 +/- 5.66 to postoperative 18.00 +/- 2.12 mmHg in glaucoma after IOL implant combined with vitrectomy operation; from preoperative 33.65 +/- 5.28 to postoperative 16.45 +/- 1.48 mmHg in juvenile glaucoma; from preoperative 31.43 +/- 4.13 to postoperative 18.13 +/- 1.25 mmHg in the failure conventional filtering surgery of glaucoma. The postoperative complicatons were flat anterior chamber, hyphema, anterior iritis and so on. CONCLUSION: The Ahmed glaucoma valve implant is a useful method in lowing IOP of refractory glaucoma.

Female↗