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Biomedical subjects

X Tan

Publications and source records attributed to X Tan.

At least 19 recordsLinked to original sources
PubMed2006

A comparative linkage map of oilseed rape and its use for QTL analysis of seed oil and erucic acid content.

We have developed a new DH mapping population for oilseed rape, named TNDH, using genetically and phenotypically diverse parental lines. We used the population in the construction of a high stringency genetic linkage map, consisting of 277 loci, for use in quantitative genetic analysis. A proportion of the markers had been used previously in the construction of linkage maps for Brassica species, thus permitting the alignment of maps. The map includes 68 newly developed Sequence Tagged Site (STS) markers targeted to the homologues of defined genes of A. thaliana. The use of these markers permits the alignment of our linkage map with the A. thaliana genome sequence. An additional 74 loci (31 newly developed STS markers and 43 loci defined by SSR and RFLP markers that had previously been used in published linkage maps) were added to the map. These markers increased the resolution of alignment of the newly constructed linkage map with existing Brassica linkage maps and the A. thaliana genome sequence. We conducted field trials with the TNDH population at two sites, and over 2 years, and identified reproducible QTL for seed oil content and erucic acid content. The results provide new insights into the genetic control of seed oil and erucic acid content in oilseed rape, and demonstrate the utility of the linkage map and population.

Brassica napus↗
PubMed2006

Novel IL-15 isoforms generated by alternative splicing are expressed in the intestinal epithelium.

Previous studies have identified mRNA three isoforms encoding interleukin-15 (IL-15) that are produced through differential splicing and encode for the same mature IL-15 protein with two different signal peptides. Our analysis of mouse intestinal epithelial cells revealed two new IL-15 mRNA isoforms generated by different alternative splicing events. In one form (IL-15DeltaE6), exon 6 is absent, and in the second form the first 48 nt of exon 7 are absent (IL-15DeltaE7) through usage of an alternative 5' splicing site within exon 7. These mRNA isoforms encoded in-frame IL-15 protein variants lacking either 15aa (IL-15DeltaE6) or 16aa (IL-15DeltaE7) both utilizing the normal long signal peptide. Significant structural changes were predicted for these new IL-15 isoforms. RNAse protection assays revealed the highest expression of isoform mRNA in the intestinal epithelium and functional analysis of recombinant IL-15 isoform proteins suggested possible regulatory functions.

Alternative Splicing↗
PubMed2006

Changes in pulmonary arteriole protein kinase calpha expression associated with supplemental L-arginine in broilers during cool temperature exposure.

The present study was conducted to examine the effect of supplemental L-arginine on pulmonary arteriole protein kinase Calpha (PKCalpha) expression in broilers exposed to cool temperature, to investigate further the molecular mechanisms of supplemental L-arginine on modulating pulmonary vascular functions in hypertensive broilers. Broilers were subjected to sub-thermoneutral (cool) temperature to induce pulmonary hypertension syndrome (PHS), and an additional 10 g/kg L-arginine was added to the basal diet to evaluate the effects of supplemental L-arginine on PHS mortality, plasma nitric oxide (NO) production and pulmonary arterioles PKCalpha expression. Supplemental L-arginine reduced PHS mortality but did not affect right/total ventricle (RV/TV) ratios in clinically healthy birds. Birds fed additional L-arginine had increased plasma NO and decreased PKCalpha protein expression in pulmonary arterioles; NO production was negatively correlated with PKCalpha expression. These results demonstrated that supplemental L-arginine diminished PKCalpha expression in birds exposed to cool temperature. It is suggested that NO-induced loss of PKCalpha expression might be partially responsible for its effects on dilating pulmonary vasculature and inhibiting pulmonary vascular remodelling in vivo.

Animals↗
PubMed2005

Sorption and complexation of Eu(III) on alumina: effects of pH, ionic strength, humic acid and chelating resin on kinetic dissociation study.

The effects of pH (pH=2-12), ionic strength (0.01-2 mol/l NaNO(3)) and humic acid on the sorption and complexation of Eu(III) on alumina were investigated by using batch techniques. The experiments were carried out at room temperature and under ambient conditions. The results indicate that the sorption of Eu(III) on alumina is strongly influenced by humic acid. The sorption of Eu(III) on alumina is significantly dependent on pH values and independent of ionic strength. The sorption of Eu(III) on alumina may be attributed to surface complexation. The species of Eu(III) on HA-alumina colloids is dominated by both HA and alumina, and the addition sequences of HA or Eu(III) to the ternary system do not influence the sorption of Eu(III) to HA-coated alumina. Kinetic dissociation of Eu(III) from bare and HA-coated alumina was also studied by using the chelating resin. The result was discussed by a pseudo-first-order kinetics model.

Journal Article↗
PubMed2005

Effects of early feed restriction and cold temperature on lipid peroxidation, pulmonary vascular remodelling and ascites morbidity in broilers under normal and cold temperature.

Two experiments were conducted to evaluate the effects of early feed restriction on lipid peroxidation, pulmonary vascular remodelling and ascites incidence in broilers under normal and low ambient temperature. In experiment 1, the restricted birds were fed 8h per day either from 7 to 14 d or from 7 to 21 d, while the controlled birds were fed ad libitum. In experiment 2, the restricted birds were fed 80 or 60% of the previous 24-h feed consumption of full-fed controls for 7 d from 7 to 14 d. On d 14, half of the birds in each treatment both in experiment 1 and experiment 2 were exposed to low ambient temperature to induce ascites. Body weight and feed conversion ratio were measured weekly. The incidences of ascites and other disease were recorded to determine ascites morbidity and total mortality. Blood samples were taken on d 14, 21, 28, 35 and 42 to measure the plasma malondialdehyde (MDA), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px). On d 42, samples were taken to determine the right/total ventricular weight ratio (RV/TV), vessel wall area/vessel total area ratio (WA/TA) and mean media thickness in pulmonary arterioles (mMTPA). Low-temperature treatment increased plasma MDA concentration. When broilers were exposed to a cool environment for 3 weeks, plasma SOD and GSH-Px activity were decreased compared with normal-temperature chicks. RV/TV, WA/TA and mMTPA on d 42 were increased in birds exposed to cold, consistent with the increased pulmonary hypertension and ascites morbidity. Early feed restriction markedly decreased plasma MDA concentration. The plasma SOD and GSH-Px activity of feed-restricted birds were markedly higher than those fed ad libitum on d 35 and d 42. All early feed restriction treatments reduced ascites morbidity and total mortality. On d 42, the RV/TV, WA/TA and mMTPA of feed-restricted broilers were lower than that of the ad libitum-fed broilers. The results suggested that early feed restriction alleviated the lipid peroxidation, promoted the activity of enzymatic antioxidant and inhibited pulmonary vascular remodelling. These changes might be associated with reduced ascites incidence.

Animals↗
PubMed2005

Involvement of MMP-7 in invasion of pancreatic cancer cells through activation of the EGFR mediated MEK-ERK signal transduction pathway.

AIMS: To clarify the involvement of matrix metalloproteinase-7 (MMP-7) in cell dissociation and the subsequent invasion of pancreatic cancer cells. METHODS: Western blotting, in vitro invasion assay, immunocytochemistry, and immunohistochemistry were performed in pancreatic cancer cell lines or pancreatic cancer tissue. RESULTS: The active form of the MMP-7 protein was expressed exclusively in the conditioned medium of dissociated (PC-1.0 and AsPC-1) pancreatic cancer cells, whereas proMMP-7 protein was only detected in the conditioned medium of non-dissociated (PC-1 and Capan-2) cells. Both intracellular and conditioned medium localised MMP-7 was greatly reduced by treatment with the epidermal growth factor receptor (EGFR) inhibitor AG1478 and the mitogen activated protein kinase kinase (MEK) inhibitor U0126 in pancreatic cancer cells. MMP-7 treatment significantly induced the disruption of tight junction (TJ) structures and subsequent cell dissociation, and activation of the EGFR mediated MEK- ERK (extracellular signal regulated protein kinase) signalling pathway in the non-dissociated pancreatic cancer cells. Moreover, the strong in vitro invasiveness of dissociated cells was inhibited by AG1478 and U0126 treatment, whereas the weak invasiveness of non-dissociated cells was apparently induced by MMP-7 treatment. In addition, MMP-7 expression was stronger at the invasive front than at the centre of human pancreatic tumours. CONCLUSION: MMP-7 is involved in cell dissociation and the subsequent invasion of pancreatic cancer cells. It induces the disruption of TJ structures and forms a positive feedback loop with activation of the EGFR mediated MEK-ERK signalling pathway.

Adenocarcinoma↗
PubMed2004

VEGF-A angiogenesis induces a stable neovasculature in adult murine brain.

Angiogenesis is a critical component of stroke, head injury, cerebral vascular malformation development, and brain tumor growth. An understanding of the mechanisms of adult cerebral angiogenesis is fundamental to therapeutic vessel modulation for these diseases. To study angiogenesis in the central nervous system, we injected an adenoviral vector engineered to express vascular endothelial growth factor (VEGF-A164) into adult murine striatum. Vector-infected astrocytes expressed VEGF-A164 resulting in vascular permeability, hemorrhage, and the formation of greatly enlarged "mother" vessels. Subsequently, endothelial cells and pericytes lining mother vessels proliferated and assembled into glomeruloid bodies, complex cellular arrays interspersed by small vessel lumens. As VEGF-A164 expression declined, glomeruloid bodies involuted through apoptotic processes to engender numerous small daughter vessels. Characterized by modestly enlarged lumens with prominent pericyte coverage, daughter vessels were distributed with a density greater than normal cerebral vessels. Daughter vessels remained stable and patent to 16 months and represented the final stage of VEGF-A-induced cerebral angiogenesis. Together, these findings provide a mechanistic understanding of angiogenesis in cerebral disease processes. Furthermore, the long-term stability of daughter vessels in the absence of exogenous VEGF-A164 expression suggests that VEGF-A may enable therapeutic angiogenesis in brain.

Adenoviridae↗
PubMed2003

Identification of genes related to invasion and metastasis in pancreatic cancer by cDNA representational difference analysis.

The difference in gene expression between the highly invasive and metastatic cell line PC-1.0 and the weakly invasive and metastatic cell line PC-1 both derived from a pancreatic ductal carcinoma induced by N-nitrosobis (2-oxopropyl) amine (BOP) in Syrian golden hamster was examined using the Representational Difference Analysis (RDA) method. Within 8 clones (cDNA fragments) successfully isolated after subtraction hybridization of PC-1 cDNA from PC-1.0, 5 clones were shown to be specific or highly expressed in PC-1.0 as confirmed by RT-PCR. Among these 5 clones, two known genes, MAP kinase kinase 2 (MKK2) and phosphatidylinositol 4-kinase (PI4K230) were detected by gene sequencing. The specific expressions of MKK2 and PI4K230 in the highly invasive and metastatic cell line PC-1.0 were confirmed by RT-PCR and Northern blotting. By adding the CM of PC1.0 which included the cancer cell dissociation factor (DF), PC-1 cells began to dissociate and migrate from the colonies, and in addition the expression of MKK2 was found to be induced. On the other hand, the expression of PI4K230 was not induced in PC-1 cells by adding the CM of PC-1.0. Interestingly, in PC-1.0 the expression of PI4K230 was completely abolished and apoptosis induced by the PI3K inhibitor wortmannin. These results suggest that both MKK2 and PI4K230 are factors of a signal transduction pathway that might play an important role related to invasion and metastasis through the induction of cell motility and/or the inhibition of apoptosis.

1-Phosphatidylinositol 4-Kinase↗
PubMed2002

Identification of cis-DNA regions controlling Bmp4 expression during tooth morphogenesis in vivo.

Epithelial-mesenchymal interactions are required for tooth formation. Bone morphogenetic protein 4 (Bmp4) is a crucial signaling molecule during this process. For better understanding of the role of the Bmp4 gene during tooth development, we studied the mechanisms that control its temporal and spatial expression during development. Using a transgenic approach, we determined that the domains which controlled Bmp4 expression in epithelium-derived ameloblasts were located in the region between 0.26 kb and 1.1 kb of the murine Bmp4 promoter. In contrast, the domains controlling Bmp4 expression in mesenchyme-derived odontoblasts and pulp cells existed in other regions of the Bmp4 gene. We have also demonstrated that the domains controlling Bmp4 expression in primordial tooth cells differ from those controlling Bmp4 expression in mature tooth tissues. The determination of unique domains by controlling the expression of the Bmp4 gene suggests that different transcriptional factors regulate the Bmp4 level at different stages during tooth morphogenesis.

Ameloblasts↗
PubMed2001

A quantitative method to measure telomerase activity by bioluminescence connected with telomeric repeat amplification protocol.

Telomerase is expected to be a new biomarker for cancer diagnosis. The telomeric repeat amplification protocol (TRAP) is a sensitive method to detect telomerase activity. However, TRAP and its modified protocols are not always suitable for measuring telomerase activity of a large number of clinical samples to diagnosis cancer because these methods generally require a time-consuming detection step such as gel electrophoresis. To improve the procedure for mass diagnosis, we applied bioluminescence to replace the detection step. Telomerase activity is measured by evaluating the amount of inorganic pyrophosphate generated in PCR amplification of telomerase elongation product, with use of the sensitive enzymatic luminometric inorganic pyrophosphate detection assay (ELIDA). TRAP connected with ELIDA (TRAP-ELIDA) can quantitatively detect telomerase activity within linearity from 2 to 1000 cell equivalents. The ELIDA signals accorded with results of TRAP-SYBR green staining, and the results of ELIDA were significantly correlated to those of TRAP connected with an enzyme-linked immunosorbent assay (TRAP-ELISA) (r(2) = 0.992, P < 0.001). TRAP-ELIDA is a simple and sensitive method to quantify telomerase activity without time-consuming gel electrophoresis. Because TRAP-ELIDA measures telomerase activity with a luminometer, it could be applied to a large number of clinical samples at the same time.

Adenosine Triphosphate↗
PubMed2001

Synthesis, structure, electrochemistry, and spectroelectrochemistry of hypervalent phosphorus(V) octaethylporphyrins and theoretical analysis of the nature of the PO bond in P(OEP)(CH(2)CH(3))(O).

A variety of phosphorus(V) octaethylporphyrin derivatives of the type [P(OEP)(X)(Y)](+)Z(-) (OEP: octaethylporphyrin) (X = CH(3), CH(2)CH(3), C(6)H(5), F; Y = CH(3), CH(2)CH(3), OH, OCH(3), OCH(2)CH(3), On-Pr, Oi-Pr, Osec-Bu, NHBu, NEt(2), Cl, F, O(-); Z = ClO(4), PF(6)) were prepared. X-ray crystallographic analysis of eleven compounds reveals that the degree of ruffling of the porphyrin core becomes greater and the average P-N bond distance becomes shorter as the axial ligands become more electronegative. Therefore, the electronic effect of the axial substituents plays a major role in determining the degree of ruffling although the steric effect of the substituents plays some role. A comparison of the (1)H NMR chemical shifts for the series of [P(OEP)(CH(2)CH(3))(Y)](+)Z(-) complexes with those of the corresponding arsenic porphyrins, which possess a planar core, indicates a much smaller ring current effect of the porphyrin core in the severely ruffled phosphorus porphyrins. The electrochemistry, spectroelectrochemistry and ESR spectroscopy of the singly reduced compounds are also discussed. The OH protons of [P(OEP)(X)(OH)](+) are acidic enough to generate P(OEP)(X)(O) by treatment with aq dilute NaOH. X-ray analysis of P(OEP)(CH(2)CH(3))(O) reveals that the PO bond length is very short (1.475(7) A) and is comparable to that in triphenylphosphine oxide (1.483 A). The features of the quite unique hexacoordinate hypervalent compounds are investigated by density functional calculation of a model (Por)P(CH(2)CH(3))(O) and (Por)P(F)(O) (Por: unsubstituted porphyrin).

Journal Article↗
PubMed2001

Influence of flanking sequence context on the mutagenicity of acetylaminofluorene-derived DNA adducts in mammalian cells.

Site-specifically modified oligodeoxynucleotides were used to explore the influence of neighboring base sequence context on the mutagenic potential of N-(deoxyguanosin-8-yl)-2-acetylaminofluorene (dG-AAF) and N-(deoxyguanosin-8-yl)-2-aminofluorene (dG-AF) in mammalian cells. Oligodeoxynucleotides ((5)(')TCCTCCTNXNCTCTC, where X is dG-AAF, dG-AF, or dG and N is C, A, G, or T) with different bases flanking the lesion were incorporated into a single-strand shuttle plasmid vector and used to establish the mutational frequency and specificity of dG-AAF and dG-AF adducts in simian kidney (COS-7) cells. Vectors containing dG-AAF promote preferential incorporation of dCMP at the site of the lesion; misincorporation of dAMP and dTMP also was observed. Mutational frequencies range from 11 to 23%. High mutational frequencies (18-23%) were observed when G or T was positioned 5' to dG-AAF and a lower frequency (11%) when C was 5' to the lesion. dCMP was predominantly incorporated opposite the dG-AF adduct when C, A, or T was 5' to the lesion; dAMP and dTMP were misincorporated at a frequency of 2-4%. With G 5' to the lesion, the overall mutational frequency for dG-AF ranged between 11 and 70%; the highest value occurred when C was the 3' flanking base, and the predominant mutation event was G --> T transversion (59%). We conclude from these experiments that dG-AAF and dG-AF promote G --> T transversions and G --> A transitions in mammalian cells. The mutational frequency and specificity of dG-AF vary significantly, depending on the nature of the bases flanking the lesion.

2-Acetylaminofluorene↗
PubMed2001

The cross-sectional study of the health effects of occupational exposure to carbon disulfide in a Chinese viscose plant.

This article presents results of carbon disulfide exposure assessment in a Chinese viscose rayon factory and represents the cross-sectional study beginning phase of the occupational epidemiological project. The authors measured external exposure levels to carbon disulfide at a Chinese viscose rayon factory and monitored results as internal exposure indexes by testing urine samples of workers exposed to carbon disulfide levels. The rate at which carbon disulfide is metabolized by exposed subjects was demonstrated by 2-thio-thiazolidine-4-carboxylic acid (TTCA) concentrations in urine of exposed subjects, which was studied to determine best time points for internal exposure sampling. Carbon disulfide concentrations in the air of the workplace were analyzed with gas chromatography with flame photometric detector (GC-FPD); presence of TTCA in urine samples of subjects was determined using a modified high-performance liquid chromatography method. Kinetics of TTCA excretion was studied by analysis at different time points during and after exposure of workers to carbon disulfide. A total of 155 personal samples were obtained. Carbon disulfide concentration at staple viscose hall was found to be 13.72 +/- 1.12 mg/m3 in terms of geometric mean and geometric standard deviation. Carbon disulfide concentration at filament spinning hall was found to be 20.05 +/- 1.33 mg/m3. TTCA values of subjects at staple spinning hall were 1.18 +/- 0.43 and 1.07 +/- 0.38 mg/g creatinine for subjects working at filament spinning hall. The best time for TTCA sampling is at the end of the exposure-working shift.

Adult↗
PubMed2001

Brownian dynamics simulations of interaction between scorpion toxin Lq2 and potassium ion channel.

The association of the scorpion toxin Lq2 and a potassium ion (K(+)) channel has been studied using the Brownian dynamics (BD) simulation method. All of the 22 available structures of Lq2 in the Brookhaven Protein Data Bank (PDB) determined by NMR were considered during the simulation, which indicated that the conformation of Lq2 affects the binding between the two proteins significantly. Among the 22 structures of Lq2, only 4 structures dock in the binding site of the K(+) channel with a high probability and favorable electrostatic interactions. From the 4 candidates of the Lq2-K(+) channel binding models, we identified a good three-dimensional model of Lq2-K(+) channel complex through triplet contact analysis, electrostatic interaction energy estimation by BD simulation and structural refinement by molecular mechanics. Lq2 locates around the extracellular mouth of the K(+) channel and contacts the K(+) channel using its beta-sheet rather than its alpha-helix. Lys27, a conserved amino acid in the scorpion toxins, plugs the pore of the K(+) channel and forms three hydrogen bonds with the conserved residues Tyr78(A-C) and two hydrophobic contacts with Gly79 of the K(+) channel. In addition, eight hydrogen-bonds are formed between residues Arg25, Cys28, Lys31, Arg34 and Tyr36 of Lq2 and residues Pro55, Tyr78, Gly79, Asp80, and Tyr82 of K(+) channel. Many of them are formed by side chains of residues of Lq2 and backbone atoms of the K(+) channel. Thirteen hydrophobic contacts exist between residues Met29, Asn30, Lys31 and Tyr36 of Lq2 and residues Pro55, Ala58, Gly79, Asp80 and Tyr82 of the K(+) channel. These favorable interactions stabilize the association between the two proteins. These observations are in good agreement with the experimental results and can explain the binding phenomena between scorpion toxins and K(+) channels at the level of molecular structure. The consistency between the BD simulation and the experimental data indicates that our three-dimensional model of Lq2-K(+) channel complex is reasonable and can be used in further biological studies such as rational design of blocking agents of K(+) channels and mutagenesis in both toxins and K(+) channels.

Amino Acid Sequence↗
PubMed2001

C1q arrests the cell cycle progression of fibroblasts in G(1) phase: role of the cAMP/PKA-I pathway.

C1q may participate in the loss of connective tissue occurring in chronic inflammatory lesions. The hypothesis of a detrimental role of C1q on cell proliferation was tested on primary cultures of human fibroblasts (HFs). C1q suppressed the DNA synthesis of HF in response to platelet-derived growth factor (PDGF) with an IC(50) of 20 microg/ml, and blocked 78% of the cycling cells in G(1) phase. The C1q block did not involve production of inhibitory prostaglandin by the cells. Given that C1q elicits signals of the adenylyl cyclase pathway in HF, we examined cAMP-dependent mechanisms to understand how C1q inhibited the PDGF response. Whereas the C1q block was enhanced by agonist dibutyryl-adenosine 3', 5'-cyclic mono-phosphate (db-cAMP), antagonist adenosine 3', 5'-cyclic monophosphorotioate triethylammonium salt (Rp-cAMP) minimized it. C1q increased the level of cAMP-dependent protein kinase I (PKA-I) 4.5-fold, without altering the activation of the extracellular-regulated protein kinase (ERK) pathway. These results demonstrate that the interactions of C1q with HF cause growth arrest at the G(1) phase through mechanisms associated with a PKA-I dependent pathway.

Adult↗
PubMed2001

Internight reliability and benchmark values for computer analyses of non-rapid eye movement (NREM) and REM EEG in normal young adult and elderly subjects.

OBJECTIVE: To determine the reliability of computer measured non-rapid eye movement (NREM) and REM frequency bands in the 0.3-45 Hz range and to provide benchmark data for these measures in young normal (YN) and elderly normal (EN) subjects (Ss). METHODS: Sleep EEG was recorded in 19 YN and 19 EN Ss on 4 non-consecutive baseline nights and simultaneously quantified as fast Fourier transform (FFT) power and 3 zero-cross period-amplitude (PA) measures: integrated amplitude, time in band and average wave amplitude. RESULTS: The shapes of both the FFT and PA spectra differed among Ss but were highly consistent within individuals. Inter-night reliability of the separate frequency bands was correspondingly high. Despite substantial age effects, the reliability of computer-measured sleep EEG in the elderly equaled that of the YN Ss. Within both the YN and EN groups, the shapes of the NREM and REM spectral curves differed significantly. The NREM and REM also differed significantly in the two age groups. CONCLUSIONS: Computer-measured sleep EEG is highly reliable across non-consecutive nights in both young and elderly normal Ss. The trait-like stability of these measures suggests they are genetically determined. This possibility is supported by twin study data that show strong heritability for FFT-measured waking EEG. The different shapes of NREM and REM spectra add further evidence that these are fundamentally different states of brain organization. The age differences in spectral shape, along with PA data for wave incidence, demonstrate that age effects on sleep EEG are not caused by changes in skull impedance or other non-cerebral factors.

Adult↗
PubMed2001

A simple method for computer quantification of stage REM eye movement potentials.

We describe a simple method for computer quantification of eye movement (EM) potentials during REM sleep. This method can be applied by investigators using either period-amplitude (PA) or Fast Fourier Transform (FFT) spectral EEG analysis without special hardware or computer programming. It provides good correlations with visual ratings of EM in baseline sleep and after administration of GABAergic hypnotics. We present baseline data for both PA and FFT measures for 16 normal subjects, studied for 5 consecutive nights. Both visually rated and computer-measured EM density (EMD) showed high night-to-night correlations across baseline and drug nights and the computer measures detected the EMD suppression that is produced by GABAergic drugs. Measurement of EM in addition to stage REM provides biologically significant information and application of this simple computer method, which does not require pattern recognition algorithms or special hardware, could provide reliable data that can be compared across laboratories.

Computers↗