Biomedical subjects

K Tang

Publications and source records attributed to K Tang.

At least 19 recordsLinked to original sources

PubMed2002

Wnt-1 promotes neuronal differentiation and inhibits gliogenesis in P19 cells.

Wnt-1, the vertebrate counterpart of the Drosophila wingless gene, plays an important role in the early morphogenesis of neural tissues. In this report, we have shown that overexpression of Wnt-1 can direct embryonic carcinoma P19 cells to differentiate into neuron-like cells in the absence of retinoic acid. Immunocytochemistry showed that these cells expressed neuronal markers, such as the neurofilament (NF) and microtubule-associated protein 2 (MAP2), but failed to express the glial cell marker, glial fibrillary acidic protein (GFAP). RT-PCR revealed that two basic helix-loop-helix (bHLH) genes, Mash-1 and Ngn-1, were up-regulated during the differentiation stage of Wnt-1-overexpressing P19 cells. These results suggest that the Wnt-1 gene promotes neuronal differentiation and inhibits gliogenesis during the neural differentiation of P19 cells, and that neural bHLH genes might be involved in this process.

Animals↗

PubMed2002

Type I bone morphogenetic protein receptors are expressed on cerebellar granular neurons and a constitutively active form of the type IA receptor induces cerebellar abnormalities.

Cerebellar granular neurons are the most abundant neuronal type in the CNS. Their number and experimental accessibility have made these neurons a valuable model for investigating mechanisms of cell proliferation and differentiation in the CNS. Proliferation of granular neurons is regulated, at least in part, by the secreted protein Sonic Hedgehog, whereas induction and differentiation both appear to be controlled by bone morphogenetic protein (BMP) signaling. Given the role of BMPs in granular cell differentiation, we postulated that BMP receptors (BMPRs) would be expressed on cerebellar granular neurons and that signaling through these receptors is required for normal differentiation. We found that both BMPRIA and BMPRIB are expressed on granular neuron precursors and on mature granular neurons in the developing cerebellum. To determine if these receptors are sufficient for granular cell induction and/or differentiation in vivo, we introduced a constitutively active BMPRIA construct into the developing cerebellum. The resulting cerebelli showed a simplified folial pattern and ectopic collections of small cells located deep in the cerebellar white matter. Phenotypic analysis demonstrated that the ectopic cells are granular neurons. From these data we suggest that signaling through the type I BMPRs occurs during normal cerebellar development and ectopic activation of this pathway affects normal granular neuron development. Furthermore, the similarity of the cerebellar anomalies arising from perturbed BMPR signaling to human cerebellar malformations suggests that dysregulation of BMP signaling may play a pathogenic role in some human cerebellar abnormalities.

Amino Acid Substitution↗

PubMed2002

A new high sensitivity thermoluminescent phosphor with low residual signal and good stability to heat treatment: LiF:Mg,Cu,Na,Si.

The preliminary investigations are reported on the characteristics of a new, high-sensitivity thermoluminescence phosphor material (LiF:Mg,Cu,Na,Si) prepared in this laboratory. The main dosimetric peak of this phosphor occurs at 197 degrees C at a heating rate of 1 degrees C.s(-1). The glow curve shape shows minimal differences and sensitivity remains stable when annealed in the range from 250 to 280 degrees C for 10 min. Its TL sensitivity to gamma radiation is about 30 times higher than that of TLD-100 with a residual signal 0.2% following a 260 degrees C readout at a heating rate of 15 degrees C.s(-1). This negligible residual signal renders LiF:Mg,Cu,Na,Si usable in unannealed form. Its TL response at both 260 degrees C and 280 degrees C are reproducible within a coefficient of variation of 2% over ten re-use cycles without systematic decrease. It retains the main advantages of LiF:Mg,Cu,P phosphor, and has a lower residual signal and a better stability to heat treatment.

Copper↗

PubMed2002

Comparative study of trapping parameters and repeatability of LiF:Mg,Cu,P (GR-200A) from different production batches.

Distinct differences in repeatability between two different production batches had been observed. The results are presented of an investigation into the change of sensitivity of LiF:Mg,Cu,P originating from 7 different production batches prepared during 1994 to 2000 after repeated usage. Computerised glow curve analysis has been used to determine the trapping parameters of these thermoluminescent materials. The sensitivity in LiF:Mg,Cu,P for all investigated batches remains stable after repeated usage. The maxima of glow peaks 2 to 4 are found at the same temperature within very small limits. The activation energy and frequency of glow peaks 2 to 4 vary little from batch to batch. For all investigated peaks, no correlation has been found between glow sensitivity and trapping parameters. The peak areas of glow peaks 3 and 4 originating from 4 batches prepared during 1996 to 2000 are significantly larger than that of the other three batches. The GR-200A LiF:Mg,Cu,P has been improved dramatically in recent years.

Copper↗

PubMed2002

Influence of readout parameters on TL response, re-usability and residual signal in LiF:Mg,Cu,P.

It has recently been recommended that heating rates do not exceed 10 K.s(-1) and that the maximum temperature of readout should not exceed 265 degrees C for LiF:Mg,Cu,P. In some cases, a decrease of sensitivity in this material in the first of several re-use cycles had been reported. Influence of heating rates up to 30 K.s(-1), duration time up to 40s and maximum readout temperatures up to 270 degrees C on TL response, re-usability and residual signal was investigated. It was found that the maximum readout temperatures above 240 degrees C may lead to the thermoluminscent response decrease in the first several re-use cycles. The readout parameters can be optimised to minimise the residual signal (less than 0.4%) and to retain a constant sensitivity at the same time at high heating rates up to 30 K.s(-1) in a short time (less than 1 min per TL chip) without the necessity of heating above 240 degrees C. A concept of 'efficient residual signal' was put forward to quantify more accurately the real residual signal which affects the precision of the next measurement.

Copper↗

PubMed2002

New advances in LiF:Mg,Cu,P TLDs (GR-200A).

In order to volume-produce LiF:Mg,Cu,P TLDs, increase the repeatability of preparation technology and further improve the features of TLDs, especially the moisture resistant property and the accuracy in ultra-low dose, the prescription and preparation techniques have been investigated further in recent years. The main features of GR-200A have been improved dramatically by adding a chemical additive and adopting a particular preparation technology. Recent improvements are presented including prescription, preparation technology, TL sensitivity, signal-to-noise rate, detection threshold, residual signal, the moisture resistant property and the uncertainty in low dose measurements. The sensitivity of GR-200A has been increased to 65 times as high as TLD-100 from the original 29 times. The residual signal has been decreased to less than 1% from the original of about 2.5% following 240 degrees C readout. The detection threshold decreases and the signal-to-noise ratio increases. The uncertainty in low dose measurements is reduced significantly. The resistance to humidity has been improved remarkably. The preparation technology to volume-produce GR-200A is stable.

Copper↗

PubMed2002

The clinical utility of nuclear medicine imaging for the detection of occult gastrointestinal haemorrhage.

Acute gastrointestinal bleeding is often intermittent and the bleeding source may be difficult to locate, resulting in delay of potentially life-saving treatment. The aim of this study was to determine the clinical utility of 99mTc labelled red blood cell imaging and [99mTc]pertechnetate (Meckel's scan) imaging in a series of 137 patients admitted over a 5 year period to hospital for management of acute gastrointestinal bleeding. Of the 137 patients, 70 had positive 99mTc red blood cell studies. Eleven of 24 patients who had imaging performed beyond 3 h had positive scans that would otherwise have been missed. Only 47 patients had a definite final diagnosis at the time of hospital discharge, of which six were negative on 99mTc red blood cell imaging. The correct site of bleeding was localized in seven of 21 patients with foregut bleeding, and 15 of 20 patients with colonic bleeding. Endoscopy yielded a diagnosis in 13 of the 47 patients (28%). Eleven patients had Meckel's scans but all were negative. Angiography was diagnostic in one of 17 patients studied. 99mTc red blood cell imaging is a useful test in the management of acute gastrointestinal bleeding. Imaging beyond 3 h may further improve the bleeding detection rate. This test, however, may be an unreliable means of localization of bleeding, particularly in the foregut.

Adolescent↗

PubMed2001

Sugar additives for MALDI matrices improve signal allowing the smallest nucleotide change (A:T) in a DNA sequence to be resolved.

Sample preparation for matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) of DNA is critical for obtaining high quality mass spectra. Sample impurity, solvent content, substrate surface and environmental conditions (temperature and humidity) all affect the rate of matrix-analyte co-crystallization. As a result, laser fluence threshold for desorption/ionization varies from spot to spot. When using 3-hydroxypicolinic acid (3-HPA) as the matrix, laser fluence higher than the threshold value reduces mass resolution in time-of-flight (TOF) MS as the excess energy transferred to DNA causes metastable decay. This can be overcome by either searching for 'hot' spots or adjusting the laser fluence. However, both solutions may require a significant amount of operator manipulation and are not ideal for automatic measurements. We have added various sugars for crystallization with the matrix to minimize the transfer of excess laser energy to DNA molecules. Fructose and fucose were found to be the most effective matrix additives. Using these additives, mass resolution for DNA molecules does not show noticeable deterioration as laser energy increases. Improved sample preparation is important for the detection of single nucleotide polymorphisms (SNPs) using primer extension with a single nucleotide. During automatic data acquisition it is difficult to routinely detect heterozygous A/T mutations, which requires resolving a mass difference of 9 Da, unless a sugar is added during crystallization.

DNA Mutational Analysis↗

PubMed2001

A multicapillary inlet jet disruption electrodynamic ion funnel interface for improved sensitivity using atmospheric pressure ion sources.

A new multicapillary inlet and ion funnel interface for electrospray ionization-mass spectrometry has been developed and demonstrated to achieve higher ion transmission efficiency compared to a single-capillary inlet and ion funnel interface. Even though the distance between the end of the ESI inlet capillary and the exit of the ion funnel (10 cm) is significantly longer than that of the conventional interface (typically a few millimeters), a significant part of the directed inlet gas flow persists into the first stage of pumping and results in an increased gas load to the second chamber. A jet disrupter made of a circular metal disk placed on axis in the ion funnel enhanced the dispersion of the directed gas flow from a multicapillary inlet and was also found to improve the ion transmission. The ion funnel with the jet disrupter demonstrated a 15% improvement in ion transmission (compared to that without the jet disrupter) and simultaneously reduced the pumping speed required for the first or second stage by a factor of 2-3. Compared to the sensitivity with the standard mass spectrometer interface (an API 3000, Sciex, Concord, ON, Canada) in MS/MS operation using an interface equipped with the jet disrupter and ion funnel, a 5.3-10.7-fold enhancement in signal was observed for samples with concentrations of 100-500 pg/microL and 10.2 to 14.1-fold enhancement for concentrations of 10 to 50 pg/microL. The decreased enhancement at higher concentrations is attributed to space charge effects and detector saturation.

Air Pressure↗

PubMed2001

A role of N-cadherin in neuronal differentiation of embryonic carcinoma P19 cells.

N-cadherin is one of the important molecules for cell to cell interaction in the development of the central nervous system (CNS). In this report, we have shown that N-cadherin mRNA and protein were increased rapidly in retinoic acid (RA)-induced neuronal differentiation of embryonic carcinoma P19 cells. To explore possible roles for N-cadherin during this process, N-cadherin-overexpressing P19 cell lines were established. These transfected cells could differentiate into neurofilament-expressing neurons in the absence of RA. RT-PCR revealed that the expression patterns of development-related genes, such as Oct-3/4, nestin, Notch-1, and Mash-1 were similar between the transfected P19 cells and the RA-induced wild-type P19 cells during their neuronal differentiation. On the contrary, the Wnt-1 gene was up-regulated in the N-cadherin-overexpressing P19 cells, but could not be detected in the wild-type P19 cells. These results suggest N-cadherin may play a role in neuronal differentiation of P19 cells, possibly through the Wnt-1 signaling pathway.

Animals↗

PubMed2001

Packed capillary reversed-phase liquid chromatography with high-performance electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry for proteomics.

In this study, high-efficiency packed capillary reversed-phase liquid chromatography (RPLC) coupled on-line with high-performance Fourier transform ion cyclotron resonance (FTICR) mass spectrometry has been investigated for the characterization of complex cellular proteolytic digests. Long capillary columns (80-cm) packed with small (3-micron) C18 bonded particles provided a total peak capacity of approximately 1000 for cellular proteolytic polypeptides when interfaced with an ESI-FTICR mass spectrometer under composition gradient conditions at a pressure of 10,000 psi. Large quantities of cellular proteolytic digests (e.g., 500 micrograms) could be loaded onto packed capillaries of 150-micron inner diameter without a significant loss of separation efficiency. Precolumns with suitable inner diameters were found useful for improving the elution reproducibility without a significant loss of separation quality. Porous particle packed capillaries were found to provide better results than those containing nonporous particles because of their higher sample capacity. Two-dimensional analyses from the combination of packed capillary RPLC with high-resolution FTICR yield a combined capacity for separations of > 1 million polypeptide components and simultaneously provided information for the identification of the separated components based upon the accurate mass tag concept previously described.

Chromatography, Liquid↗

PubMed2001

Generation of multiple electrosprays using microfabricated emitter arrays for improved mass spectrometric sensitivity.

Arrays of microelectrospray emitters were fabricated on polycarbonate substrates using a laser etching technique. Stable multielectrosprays were successfully generated in the liquid flow rate range relevant to mass spectrometric applications. Comparison of electrosprays generated from the microfabricated emitter array and conventional fused-silica capillaries showed similar spray characteristics and reliability. Higher total electrospray ion currents were observed as the number of electrosprays increased at a given total liquid flow rate. Consistent with the theoretical prediction, the total spray current at a constant total liquid flow rate was shown experimentally to be approximately proportional to the square root of the number of electrosprays. It is further projected that when total flow rate is optimized the maximum achievable total current will be proportional to the number of emitters. Evaluation of the multielectrospray device using a triple quadrupole mass spectrometer showed a factor of 2-3 sensitivity enhancement for the spray numbers ranging from two to nine compared to a conventional single electrospray ionization source under the same operating conditions.

Algorithms↗

PubMed2001

The anti-anginal drug fendiline increases intracellular Ca(2+) levels in MG63 human osteosarcoma cells.

The effect of fendiline, an anti-anginal drug, on cytosolic free Ca(2+) levels ([Ca(2+)](i)) in MG63 human osteosarcoma cells was explored by using fura-2 as a Ca(2+) indicator. Fendiline at concentrations between 1 and 200 microM increased [Ca(2+)](i) in a concentration-dependent manner and the signal saturated at 100 microM. The Ca(2+) signal was inhibited by 65+/-5% by Ca(2+) removal and by 38+/-5% by 10 microM nifedipine, but was unchanged by 10 microM La(3+) or verapamil. In Ca(2+)-free medium, pre-treatment with 1 microM thapsigargin (an endoplasmic reticulum Ca(2+) pump inhibitor) to deplete the endoplasmic reticulum Ca(2+) store inhibited fendiline-induced intracellular Ca(2+) release. The Ca(2+) release induced by 50 microM fendiline appeared to be independent of IP(3) because the [Ca(2+)](i) increase was unaltered by inhibiting phospholipase C with 2 microM U73122. Collectively, the results suggest that in MG63 cells fendiline caused an increase in [Ca(2+)](i) by inducing Ca(2+) influx and Ca(2+) release in an IP(3)-independent manner.

Calcium↗

PubMed2001

DNA sequencing and genotyping by transcriptional synthesis of chain-terminated RNA ladders and MALDI-TOF mass spectrometry.

Sets of RNA ladders can be synthesized by transcription of a bacteriophage-encoded RNA polymerase using 3'-deoxynucleotides as chain terminators. These ladders can be used for sequencing of DNA. Using a nicked form of phage SP6 RNA polymerase in this study substantially enhanced yields of transcriptional sequencing ladders. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) of chain-terminated RNA ladders allowed DNA sequence determination of up to 56 nt. It is also demonstrated that A-->G and C-->T variations in heterozygous and homozygous samples can be unambiguously identified by the mass spectrometric analysis. As a step towards single-tube sequencing reactions, alpha-thiotriphosphate nucleotide analogs were used to overcome problems caused by chain terminator-independent, premature termination and by the small mass difference between natural pyrimidine nucleotides.

Base Sequence↗

PubMed2001

Dopamine-dependent synaptic plasticity in striatum during in vivo development.

The neurotransmitters dopamine (DA) and glutamate in the striatum play key roles in movement and cognition, and they are implicated in disorders of the basal ganglia such as Parkinson's disease. Excitatory synapses in striatum undergo a form of developmental plasticity characterized by a decrease in glutamate release probability. Here we demonstrate that this form of synaptic plasticity is DA and DA D2 receptor dependent. Analysis of spontaneous synaptic responses indicates that a presynaptic mechanism involving inhibition of neurotransmitter release underlies the developmental plasticity. We suggest that a major role of DA in the striatum is to initiate mechanisms that regulate the efficacy of excitatory striatal synapses, producing a decrease in glutamate release.

Animals↗

PubMed2001

Spontaneous spinal epidural abscess in a neonate. With a review of the literature.

Spinal epidural abscess is uncommon in neonates and infants, and is usually related to previous lumbar puncture or epidural anaesthesia. Diagnosis is often delayed because of the non-specific presentation. We present a 7-week-old girl who developed paraplegia 3 weeks after transient fever and a self-limiting skin rash. MR imaging revealed an epidural contrast-enhancing lesion compressing the spinal cord. At operation, an organised granulated abscess was identified with Staphylococcus aureus the causative organism. Laminectomy and removal of the organised abscess and systemic intravenous antibiotics resulted in complete neurological recovery. The patient did not develop late spinal deformity following the decompressive laminectomy. The rapid onset of paraplegia can often be missed in such a young child but should be promptly investigated, as surgical treatment of cord compression carries an excellent prognosis for neurological recovery. We review the literature on the initial presentation, usual investigations, causative organisms and surgical management of paediatric spinal epidural abscesses.

Epidural Abscess↗

PubMed2001

Isolation and characterization of a novel cDNA, UBAP1, derived from the tumor suppressor locus in human chromosome 9p21-22.

PURPOSE: To clone the putative tumor suppressor gene(s) in a refined region at 9p21-22 undergoing loss of heterozygosity in nasopharyngeal carcinoma (NPC). METHODS: We systematically screened the expression patterns of 25 novel ESTs (expressed sequence tags) in a minimal common deleted region of 9p21-22 in NPC. One of these ESTs was found down-regulated in NPC. Subsequently, the corresponding gene sequence of this EST was established by cDNA cloning and RACE (rapid amplification of cDNA end) procedures. Furthermore, a mouse homologue of this gene was identified. The expression of this gene was examined using Northern blot or reverse transcription-polymerase chain reaction (RT-PCR) in various human and mouse tissues. A limited screen for mutation of coding sequence of this novel human gene was undertaken using RT-PCR and direct sequencing analysis. RESULTS: A novel gene was cloned. This gene is a new member of the UBA domain family, so we named it UBAPI for ubiquitin-associated protein 1 (HUGO Gene Nomenclature Committee-approved symbol). Northern blot and RT-PCR analysis demonstrate a ubiquitous pattern of gene expression in human and mouse tissues. The direct sequencing analysis of the coding region of hUBAP1 following RT-PCR failed to reveal any mutations in a preliminary screen of NPC cell line HNE1 and primary nasopharyngeal carcinoma samples. CONCLUSIONS: We cloned a novel gene UBAPI, which is highly conserved between human and mouse. Clearly, as a novel member of UBA domain protein family and taking its map location into account, a more extensive analysis is essential to establish whether subtle mutations are present in nasopharyngeal carcinomas.

Amino Acid Sequence↗

PubMed2001

Transgenic rice plants expressing the ferredoxin-like protein (AP1) from sweet pepper show enhanced resistance to Xanthomonas oryzae pv. oryzae.

We used particle bombardment to cotransform mature seed-derived rice callus (Oryza sativa L., ssp. japonica, cv. Eyi 105) with plasmids containing the linked marker genes gusA and hpt, and the ap1 gene encoding an amphipathic protein previously shown to delay the hypersensitive response induced in non-host plants by the pathogen Pseudomonas syringae pv. syringae (Pss). Thirty-two independent lines of transgenic rice plants were regenerated, and 27 of these lines carried all three transgenes as shown by molecular analysis. A bacterial blight inoculation test was carried out on ten lines. In each case, plants carrying the ap1 gene showed enhanced resistance to Xanthomonas oryzae pv. oryzae (Xoo) race 6 at various levels. This suggests the ap1 gene could be a useful candidate for genetic engineering strategies in rice to provide bacterial blight resistance.

Journal Article↗