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Y Xia

Publications and source records attributed to Y Xia.

At least 307 records · Page 17Linked to original sources
PubMed1993

Neuroanatomical distribution and binding properties of saxitoxin sites in the rat and turtle CNS.

Since saxitoxin (STX) binds to voltage-sensitive sodium channels and blocks their function, it has been widely used in the study of these channels. There is, however, limited information on STX binding properties and the neuroanatomical distribution of the Na+ channel as a function of brain region in the rat and in lower vertebrates such as the turtle. In the present study, we used a broad range of 3H-STX concentration (up to 64 nM) to examine saturation profiles and density distribution in both adult rat and turtle brains. We found that (1) STX sites do not vary greatly in affinity (most Kds = 2 to 5 nM) in various regions of the adult rat brain; (2) STX binding distribution was very heterogeneous in the rat with much higher density in the cortex, hippocampus, amygdala, and cerebellum than in the brainstem and spinal cord; (3) STX sites are mostly localized in layers made mostly of neurons with low density in white matter; and (4) turtle brain STX sites had similar binding properties, but its brain had much fewer STX sites than the rat, especially in the cerebellum and rostral areas such as the cortex. We conclude that (a) adult brain sodium channels have similar STX binding affinity in spite of the existence of multiple sodium channel subtypes; (b) the brainstem is very different from rostral brain areas in channel density; and (c) the turtle brain has a much lower sodium channel density than the rat brain.

Animals↗
PubMed1993

Cloning two isoforms of rat cyclooxygenase: differential regulation of their expression.

Two isoforms of cyclooxygenase (COX) have been identified in eukaryotic cells: COX-1 encoded by a 2.8-kb mRNA, and a mitogen-inducible COX-2 encoded by a 4-kb mRNA. We have cloned the COX-1 and COX-2 cDNAs from the cDNA library constructed from lipopolysaccharide (LPS)-stimulated rat peritoneal macrophages. The deduced amino acid sequence showed that COX-1 contained 602 amino acids, whereas COX-2 contained 604 amino acids. There is 95% conservation of the nucleotide sequence in the open reading frame of COX-1 between the rat and the mouse, while the homology of the 3' untranslated region is 68% except for a 150 bp segment adjacent to the stop codon which is nonhomologous with the mouse. Transfection of both COX cDNAs into Cos-7 cells resulted in increased COX activity. In rat vascular smooth muscle cells, interleukin-1 beta selectively increased the expression of COX-2, but not that of COX-1, as assessed by enzyme activity, immunoprecipitation of COX proteins, and mRNA analysis. Only the brain among tissues tested exhibits basal expression of COX-2 as the major form of the enzyme. However, COX-2 mRNA was expressed in vivo in the lung and kidney, but not in the heart, after systemic administration of LPS, suggesting that COX-2 but not COX-1 plays a major role in producing COX-derived products of arachidonic acid during endotoxic shock. Thus, the two COX isoforms were differentially expressed, and COX-2 was selectively induced in response to inflammatory stimuli in rats.

Amino Acid Sequence↗
PubMed1993

Genomic structure, chromosomal location, and evolution of the mouse Hox 8 gene.

We isolated genomic clones containing the mouse Hox 8 gene, a member of the msh gene family. We show that Hox 8 comprises two exons of approximately 600 and 691 bp separated by a 3.5-kb intron, and that it cosegregates with previously mapped markers in the distal region of mouse chromosome 13. In midgestation embryos, the Hox 8 gene produces transcripts of 1.4 and 2.2 kb. Both transcripts are present in facial tissues of the newborn mouse, though the ratio of the 2.2-kb transcript to the 1.4-kb transcript is reduced relative to the ratio observed for midgestation embryos. An alignment of the homeobox sequences of previously characterized members of the msh family revealed three subclasses: Hox 7-like genes, Hox 8-like genes, and msh-like genes. Both the Hox 7-like genes and Hox 8-like genes are present throughout the vertebrates. Representatives of the third subclass, the msh-like genes, are found in a protostome (Drosophila) and a deuterostome (Ciona) and are thus likely to be phylogenetically widespread. To investigate the distribution of Hox 8-like genes outside the chordates, we used the polymerase chain reaction and degenerate Hox 8 primers to screen genomic DNA of the purple sea urchin (Strongylocentrotus purpuratus, Phylum Echinodermata). We isolated a gene with greater sequence similarity to mouse Hox 8 than to members of the Hox 7 or msh subfamilies, demonstrating that the Hox 8 subfamily has been in existence at least since the echinoderms diverged from the lineage that gave rise to the chordates.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1993

Adenine DNA methyltransferase M.CviRI expression accelerates apoptosis in baculovirus-infected insect cells.

The adenine DNA methyltransferase M.CviRI (TGCmA) gene from chlorella virus XZ-6E was cloned into the Autographa californica nuclear polyhedrosis virus (AcMNPV) genome and expressed in Spodoptera frugiperda insect cells under the control of two tandemly arranged viral promoters, the early ETL promoter and the late polyhedrin promoter. M.CviRI activity was first detected at 10 hr p.i and reached a maximum at 48 hr p.i. Viral DNA synthesized in insect cells infected with M.CviRI expressing virus (AcMTRI) was methylated at all TGCA sites. Unexpectedly, AcMTRI-infected cells lysed 48 hr earlier than wild-type AcMNPV-infected cells. Moreover, cellular DNA, but not viral DNA, from AcMTRI-infected cells was degraded to fragment sizes characteristic of apoptosis. These results suggest that M.CviRI methylation influences the onset of viral cytopathic effects and induces an apoptosis-like response.

Amino Acid Sequence↗
PubMed1993

Evidence for the existence of two forms of alpha 2A-adrenoceptors in the rat.

The alpha 2A-adrenoceptors in rat spleen, kidney, spinal cord and cerebral cortex were studied using [3H]-RX821002 radioligand binding. In the spleen, spinal cord and cerebral cortex, the ligand bound to saturable sites with a Kd of about 1 nmol/l and capacities of 134, 240 and 290 fmol/mg protein, respectively. Computer modelling competition curves for 39 drugs, including those for alpha 2A-, alpha 2B- or alpha 2C-adrenoceptor selective drugs, indicated that the sites labelled by [3H]-RX821002 in the spleen consisted of a single population of alpha 2A-adrenoceptors. However, the competition curves for guanoxabenz were definitely biphasic and resolved into two site fits, indicating that guanoxabenz was binding to both high affinity (Kd = 35 nmol/l) and low affinity (Kd = 8900 nmol/l) alpha 2A-adrenoceptor sites in the proportions 57% and 43%, respectively. The KdS for a number of alpha 2-adrenoceptor subtype selective drugs, measured in competition with [3H]-RX821002 in cerebral cortex and spinal cord, were highly correlated with those obtained in the spleen indicating their alpha 2A-adrenoceptor nature. However, by contrast to the results with the spleen, the guanoxabenz competition curves for the spinal cord and cerebral cortex were monophasic and resolved only into one site fits, the Kd of guanoxabenz being about 4000 nmol/l for both tissues. Drug KdS for kidney alpha 2A-adrenoceptors were also determined using [3H]-RX821002. For nearly all drugs tested, the KdS were highly correlated with those found for the alpha 2A-adrenoceptors in the other rat tissues.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic alpha-Antagonists↗
PubMed1993

GABA transporter mRNA: in vitro expression and quantitation in neonatal rat and postmortem human brain.

A previously isolated rat cDNA clone encoding the membrane transporter for the neurotransmitter gamma-aminobutyric acid was expressed in transfected COS cells. The resultant transporter protein was characterized kinetically and pharmacologically. The apparent Kt (6.1 microM) and the pharmacological profile of a neuronal-type transporter observed in these mammalian cells were consistent with previous data obtained in Xenopus laevis oocytes. Post-natal levels of gamma-aminobutyric acid transporter mRNA in rat cerebellum, cerebral cortex and striatum (as measured by nuclease protection assay) transiently exceeded levels present in the adult brain. Human gamma-aminobutyric acid transporter mRNA also was measured by nuclease protection assay using as probe a human transporter cDNA homolog obtained by polymerase chain reaction. These studies suggest that quantitation of rat and human gamma-aminobutyric acid transporter mRNAs may provide a useful index of transporter gene expression.

Adult↗
PubMed1993

Further evidence for the existence of two forms of alpha 2B-adrenoceptors in rat.

Analysis of saturation isotherms of the novel alpha 2-adrenoceptor antagonist radioligand [3H]-MK 912 revealed that the ligand labelled a homogenous population of alpha 2B-adrenoceptors in the neonatal rat lung with a Kd of 0.77 nM and a Bmax of 231 fmol/mg protein. In rat kidney, combined saturation and competition experiments, using [3H]-MK 912 and the alpha 2A-adrenoceptor selective drug guanfacine, revealed that approximately 81% of the sites labelled by [3H]-MK 912 were alpha 2B-adrenoceptors and approximately 19% alpha 2A-adrenoceptors; the Kds of [3H]-MK 912 being 1.1 and 2.0 nM and the Bmax 134 and 33 fmol/mg protein, respectively. The kidney alpha 2B-adrenoceptors were studied separately by using approximately 1.5 nM [3H]-MK 912 in the presence of 0.32 microM guanfacine, the latter which blocked ligand binding to alpha 2A-adrenoceptors completely. Analysis of drug competition curves obtained during these conditions revealed that 18 out of 20 different agonists and antagonists yielded steep and uniphasic competition curves which modelled best into one site fits. However, both guanoxabenz and LT 11 appeared to inhibit [3H]-MK 912 binding at two sites; the Kds of guanoxabenz differing approximately 120-fold and that of LT 11 differing approximately 35-fold for the two sites. Moreover, the addition of mutual fixed concentrations of either 20 microM guanoxabenz or 20 microM LT 11 completely prevented the binding of the other compound to its high affinity site, indicating that both compounds labelled the same site with the high affinity. The analysis indicated that 29% of the sites were of high and 71% of low affinity. However, in the neonatal rat lung guanoxabenz and LT 11 (as well as 15 other compounds) yielded competition curves which modelled only into one site fits. The Kds obtained in the lung correlated well with the Kds obtained in the kidney for alpha 2B-adrenoceptors; for guanoxabenz and LT 11 the values from the lung were close to those determined in the kidney for the low affinity site for guanoxabenz and LT 11. Moreover, when the rat RNG alpha 2B-adrenoceptor was expressed in COS-7 cells and its binding properties tested using [3H]-MK 912 binding, guanoxabenz, LT 11 as well as a number of other drugs inhibited the ligand binding at a single alpha 2-adrenoceptor site; the drug Kds being practically the same as those found for the neonatal rat lung. It is suggested that rat alpha 2B-adrenoceptors may exist in two forms: alpha 2B1 and alpha 2B2.(ABSTRACT TRUNCATED AT 400 WORDS)

Adrenergic alpha-Antagonists↗
PubMed1993

LPS-induced MCP-1, IL-1 beta, and TNF-alpha mRNA expression in isolated erythrocyte-perfused rat kidney.

The capacity of the lipopolysaccharide (LPS)-stimulated isolated erythrocyte-perfused rat kidney (IEPK) to produce monocyte chemoattractant protein-1 (MCP-1), interleukin-1 beta (IL-1 beta), and tumor necrosis factor-alpha (TNF-alpha) mRNA was investigated. The IEPK was chosen to exclude the influence of circulating neutrophils and monocytes that can produce both these mediators when exposed to LPS. The control minimal LPS group (LPS < 10 pg/ml) showed a small increase in mRNA expression for MCP-1, IL-1 beta, and TNF-alpha in the cortex and medulla after 80 min of perfusion when compared with the unperfused left kidney in which no IL-1 beta or TNF-alpha mRNA and only minimal amounts of MCP-1 mRNA were detected. LPS stimulation (1 microgram/ml for 40 or 80 min) increased MCP-1, IL-1 beta, and TNF-alpha mRNA expression, which was found predominately in peritubular capillary endothelial cells by in situ hybridization. The changes were not due to a marked perturbation of LPS on renal hemodynamics. The renal vascular resistance (RVR) remained constant (40 min LPS exposure) or increased only slightly during the last 5-10 min (80 min LPS exposure) compared with a progressive increase in RVR of the minimal LPS group. The hemodynamic effects of LPS on the IEPK appear to counteract the gradual increase in RVR seen in the minimal LPS group.

Animals↗
PubMed1993

Sulfonylurea receptor expression in rat brain: effect of chronic hypoxia during development.

Sulfonylurea receptors are believed to be related to ATP-sensitive potassium channels and play a key role during hypoxia/ischemia in the CNS. Our previous work has shown that these receptors in rat brainstem neurons are more important in the adult rat than in the newborn during hypoxia. In the present study, we studied the time course of postnatal development of sulfonylurea receptors in detail and the effect of chronic hypoxia on receptor density in newborn pups and adult rats exposed to hypoxia either as fetuses or as 90-d-old rats using receptor binding and autoradiography. Our current results show that sulfonylurea receptor density 1) was very low at birth and developed fast within the first 2 postnatal wk and then gradually reached adult levels and 2) continued to increase in the cortex and cerebellum but decreased in the brainstem with little or no change in other areas after postnatal wk 5. Chronic hypoxia 1) decreased body weight, brain size, and brain protein concentration and 2) increased sulfonylurea receptor density in utero but had much less of an effect in the adult. From these data, we conclude that sulfonylurea receptors develop mostly in the first 2 wk postnatally and chronic hypoxia increases sulfonylurea receptor expression in utero in spite of the fact that overall protein decreases.

ATP-Binding Cassette Transporters↗
PubMed1993

[The pain components of somatosensory evoked potentials induced by median nerve stimulation P200-N300].

The pain components of somatosensory evoked potentials (SEPs) of induced by median nerve stimulation were studied with the way of blocking bloodstream of arm in 12 normal adults. The SEPs following the painful stimuli (0.1 msec. square wave pulse) of the right wrist were recorded from the left parietal (C3') and frontal (F3) scalp with earlobe reference electrode. The pressure of 40 mmHg above the arterial pressure was given to the right upper arm by sphygmomanometer. The result showed that the P200-N300 components (latency 234 +/- 13 msec. and 308 +/- 23 msec.) of the SEPs persisted and the others disappeared when tactile sensation disappeared but pain existed. The morphology of P200-N300 from F3 was same to that from C3'. It suggested the P200-N300 were the pain potentials of median nerve SEPs.

Adult↗
PubMed1992

Dopamine transporter mRNA content in human substantia nigra decreases precipitously with age.

The dopamine transporter is the primary means of inactivating synaptic dopamine as well as a major site of action for psychostimulants (such as cocaine and amphetamine) and for neurotoxins that induce parkinsonism. In the present study, a human dopamine transporter partial cDNA clone obtained by polymerase chain reaction exhibited 87% and 89% identity at the nucleic acid and amino acid levels, respectively, with transmembrane domains 3-5 of the rat homolog. This clone was used to quantitate human dopamine transporter mRNA by nuclease protection assay. The postmortem content of dopamine transporter mRNA in the substantia nigrae of 18- to 57-yr-old subjects was relatively constant, while in subjects greater than 57 yr old, a precipitous (greater than 95%) decline in substantia nigra dopamine transporter mRNA was evident. In contrast, tyrosine hydroxylase mRNA in the same samples declined in a linear manner with increasing age. In situ hybridization experiments confirmed the profound loss of dopamine transporter gene expression in melanin-positive (presumptive dopamine) nigral neurons. These data may begin to shed light on compensatory changes occurring in human dopamine neurons during normal aging.

Adult↗
PubMed1992

Predicting protein secondary structure using neural net and statistical methods.

A comparison of neural network methods and Bayesian statistical methods is presented for prediction of the secondary structure of proteins given their primary sequence. The Bayesian method makes the unphysical assumption that the probability of an amino acid occurring in each position in the protein is independent of the amino acids occurring elsewhere. However, we find the predictive accuracy of the Bayesian method to be only minimally less than the accuracy of the most sophisticated methods used to date. We present the relationship of neural network methods to Bayesian statistical methods and show that, in principle, neural methods offer considerable power, although apparently they are not particularly useful for this problem. In the process, we derive a neural formalism in which the output neurons directly represent the conditional probabilities of structure class. The probabilistic formalism allows introduction of a new objective function, the mutual information, which translates the notion of correlation as a measure of predictive accuracy into a useful training measure. Although a similar accuracy to other approaches (utilizing a mean-square error) is achieved using this new measure, the accuracy on the training set is significantly and tantalizingly higher, even though the number of adjustable parameters remains the same. The mutual information measure predicts a greater fraction of helix and sheet structures correctly than the mean-square error measure, at the expense of coil accuracy, precisely as it was designed to do. By combining the two objective functions, we obtain a marginally improved accuracy of 64.4%, with Matthews coefficients C alpha, C beta and Ccoil of 0.40, 0.32 and 0.42, respectively. However, since all methods to date perform only slightly better than the Bayes algorithm, which entails the drastic assumption of independence of amino acids, one is forced to conclude that little progress has been made on this problem, despite the application of a variety of sophisticated algorithms such as neural networks, and that further advances will require a better understanding of the relevant biophysics.

Bayes Theorem↗
PubMed1992

The translocation (1;14)(p34;q11) in human T-cell leukemia: chromosome breakage 25 kilobase pairs downstream of the TAL1 protooncogene.

Nearly 30 percent of patients with T-cell acute lymphoblastic leukemia (T-ALL) exhibit a tumor-specific rearrangement of the TAL1 gene (also called TCL5 or SCL). These rearrangements are generated by either local DNA deletion or a (1;14)(p34;q11) chromosome translocation, and they typically result in structural alterations of the TAL1 transcription unit. In this report we present a molecular characterization of the t(1;14)(p34;q11) from a T-ALL patient. As a consequence of the translocation, TAL1 is transposed from its normal position on chromosome 1 into the T-cell receptor alpha/delta chain locus on chromosome 14. Unlike previous cases, the chromosome 1 breakpoint in this patient did not disrupt the continuity of the TAL1 transcription unit, but instead occurred approximately 25 kilobase pairs (kb) downstream of TAL1. This observation suggests that malignant alteration of TAL1 can be mediated by long-range cis-activating mechanisms that are triggered by DNA rearrangement at a distant site. Genes Chrom Cancer 4:211-216 (1992).

Base Sequence↗
PubMed1992

"One-shot" velocity microscopy: NMR imaging of motion using a single phase-encoding step.

The use of the pulsed gradient spin-echo sequence in NMR microscopy enables the measurement of molecular translational motion and simultaneous construction of velocity and self-diffusion images, a technique that has been termed dynamic NMR microscopy. In this method the PGSE contrast gradient is stepped in a fourth dimension (q space) and so is inherently inefficient. Provided that one is prepared to sacrifice some of the additional information provided by the multiple PGSE gradient approach, it is possible to construct a velocity image alone by means of a single PGSE phase-encoding step. We illustrate applications of this method in which a signal from the stationary spins is nulled by the use of both gradient phase cycling and a final "z-storage" rf pulse. The limits to velocity resolution are around 10 microns s-1 in free water but can be considerably smaller for molecules with a low self-diffusion coefficient. We demonstrate this method in a study of water capillary flow at 12 microns transverse pixel resolution, extending the velocity range by employing a four-quadrant analysis method. This method is also used to measure vascular transport in a living plant and find a flow rate of around 45 microns s-1.

Diffusion↗