Biomedical subjects

Z Tan

Publications and source records attributed to Z Tan.

At least 19 recordsLinked to original sources

PubMed2006

The miscarriage-associated HLA-G -725G allele influences transcription rates in JEG-3 cells.

BACKGROUND: HLA-G is a non-classical HLA with important immunomodulatory roles in pregnancy. A polymorphism in the promoter region, -725G, was previously associated with sporadic miscarriage in women who were unselected with respect to reproductive history. In this study, the transcription levels of different HLA-G promoter haplotypes were examined to determine whether the miscarriage-associated -725G allele influences transcription. METHODS: Five naturally occurring promoter haplotypes and three variant haplotypes created by site-directed mutagenesis were sub-cloned into luciferase expression vectors and transfected into JEG-3 cells. Expression levels of these eight haplotypes were examined in cultured cells before and after treatment with interferon-beta (IFN-beta), cytosine-5-DNA methyltransferase (M. SssI) and 5-aza-2'-deoxycytidine. Differences in expression levels between haplotypes were determined by analysis of variance (ANOVA). RESULT: Promoter haplotypes with the miscarriage-associated -725G allele were expressed at significantly higher levels in all culture conditions compared with otherwise identical haplotypes that had a -725C or -725T allele. CONCLUSION: Variation in the HLA-G promoter region influences transcription rates. Contrary to expectations, increased expression of HLA-G may be disadvantageous in some pregnancies.

Abortion, Spontaneous↗

PubMed2004

Conservation of the genomic structure and receptor-mediated signaling between human and rat IL-24.

IL-24/MDA-7 is a new member of the IL-10 family of cytokines, which signals through two heterodimeric receptor complexes (IL-20R1/IL-20R2 and IL-22R/IL-20R2). Previously, we identified a rat gene named mob-5, which encodes a secreted protein that shares a high degree of homology with human IL-24. Expression of mob-5 and its putative cell surface receptors was shown to be upregulated by oncogenic ras. Here we show that not only do rat mob-5 and human IL-24 share a strikingly similar genomic structure but also that the rat MOB-5 protein can bind to and signal through the human IL-24 receptors. Like human IL-24, binding of the rat MOB-5 protein to the human IL-24 receptors leads to activation of the JAK/STAT pathway, which in turn supports receptor-dependent survival and proliferation of Ba/F3 cells. Furthermore, using human colon cancer cell lines with somatic knockout of either the mutant or the wild-type k-ras allele, we demonstrate that the human IL-24 receptors also are upregulated by oncogenic ras. Taken together, these results provide strong experimental evidence that MOB-5 is indeed the rat homolog of human IL-24.

Amino Acid Sequence↗

PubMed2003

The sugary-type isoamylase gene from rice and Aegilops tauschii: characterization and comparison with maize and arabidopsis.

Genes for an isoamylase-like debranching enzyme have been isolated from rice and Aegilops tauschii, the donor of the D genome to wheat. The structures of the genes are very similar to each other and to the maize SU1 isoamylase gene and consist of 18 exons spread over approximately 7.5 kb. Southern analysis and fluorescent in situ hybridization showed the Ae. tauschii gene to be located in the proximal region of the short arm of chromosome 7D, thus showing synteny with the localization of the rice isoamylase gene on rice chromosome 8. Analysis of the expression pattern of wheat sugary isoamylase genes indicates that they are strongly expressed in the developing endosperm 6 days after flowering. Three distinct Sugary-type cDNA sequences were isolated from the wheat endosperm that are likely to correspond to the products of the three genomes. The deduced amino acid sequence of rice and wheat Sugary-type isoamylase is compared with other sequences available in the database and the results demonstrate that there are three types of isoamylase sequences in plants: those containing 18 exons (the Sugary-type isoamylase gene), those containing 21 exons, and those containing only 1 exon. It is possible that different combinations of isoamylase genes are expressed in different tissues.

Amino Acid Sequence↗

PubMed2001

[Experimental study of in osteogenesis in duced by NIH-3T3 cells transfected with bone morphogenetic protein 3 gene].

OBJECTIVE: To investigate the gene expression, protein synthesis and inducing osteogenetic capacity of NIH-3T3 cells transfected with recombinant human bone morphogenetic protein 3 (rhBMP3) gene. METHODS: Gene recombination technique was used to clone the BMP3 cDNA into PcDNA3 vector directly, and to form a recombined BMP3-PcDNA3 cDNA, which was introduced into NIH-3T3 cells by means of lipofectamine transfer. The total RNA of transfected NIH-3T3 cells was then extracted to verify the mRNA expression of BMP3 using Northern blot method. BMP3 protein synthesis and AKP activity in the transfected cells was checked. Then, the NIH-3T3 cells transfected with BMP3 gene were injected into nude mouse muscle to evaluate the inducing osteogenesis in the muscle. RESULTS: BMP3 gene had been inserted into PcDNA3 vector successfully. There was BMP3 mRNA expression in the total RNA of NIH-3T3 cells with the peak level appearing in the 6th week after transfection, and BMP3 protein was found in NIH-3T3 cells, and the AKP level is much higher in the transfected NIH-3T3 cells than in non-transfected NIH-3T3 cells. Histologic examination revealed that there were a large number of chondrocytes and trabeculae seen in the nude mouse muscle 4 weeks after injection of the transfected NIH-3T3 cells. CONCLUSION: BMP3 is a protein that possesses osteogenetic effect. After transfection with BMP3-PCDNA3, BMP3 mRNA expression and protein formation can be found in NIH-3T3 cells, and the transfected NIH-3T3 cells have the effect of inducing osteogenesis in vivo.

3T3 Cells↗

PubMed2001

Synthesis and evaluation of novel aldose reductase inhibitors: Effects on lens protein kinase Cgamma.

PURPOSE: To synthesize novel aldose reductase inhibitors (ARI) that will normalize losses in protein kinase Cgamma (PKCgamma) observed during diabetes and galactosemia. METHODS: ARI were synthesized as tricyclic pyrones 1-6 (HAR-1 through HAR-6) from 3-methyl-1H,7H-5a,6,8,9-tetrahydro-1-oxopyrano[4,3-b][1]benzopyran and (5aS,7S)-7-isopropenyl-3-methyl-1H,7H-5a,6,8,9-tetrahydro-1-oxopyrano[4,3-b][1]benzopyran and were tested by inhibition of aldose reductase enzyme activity in vitro and by inhibition of polyol formation in lens epithelial cells in culture. Identified compounds were further tested in galactosemic rat lens in vivo for (a) normalized PKCgamma levels by Western blot, (b) reduction of phosphorylation of the gap junction protein Cx46 by analyses of co-immunoprecipitated proteins, and (c) by normalization of gap junction activity as measured by dye transfer. RESULTS: HAR-1 (1H,7H-5a,6,8,9-tetrahydro-1-oxopyrano[4,3-b][1]benzopyran-3-acetic acid) was identified as an ARI with IC50 for aldose reductase inhibition at 2 nM. Polyol accumulation in lens epithelial cells was reduced by 80% at 10 microM. Rats fed 40% galactose for 9 days had an 80% reduction in PKCgamma levels which were normalized by HAR-1 at 100 mg/kg/day, fed orally. Phosphorylation of Cx46 was increased by 50% and this was normalized in HAR-1 treated rats (6 day treatment). Gap junction activity of galactosemic rats was reduced by 55% and this was normalized by HAR-1 in six day-treated rats. CONCLUSIONS: HAR-1 is a novel ARI which normalized losses of PKCgamma, changes in Cx46 phosphorylation, and gap junction activity.

Acetates↗

PubMed2001

Downregulation of free ubiquitin: a novel mechanism of p53 stabilization and neuronal cell death.

Neuronal death through activation of the p53 stress response pathway has been implicated in the pathogenesis of neurodegenerative disorders. The mechanisms regulating p53 accumulation and function in neurons are poorly understood. Recent evidence has demonstrated that Mdm2 is a major inhibitor of p53 that binds to and targets p53 for ubiquitin-mediated degradation. Here we demonstrate increased expression and co-localization of p53 and Mdm2 in the nuclei of degenerating neurons following treatment with either the excitotoxin, kainic acid, or the topoisomerase I inhibitor, camptothecin. Co-immunoprecipitation studies showed that p53-Mdm2 complexes were present in neuronal lysates. Dual immunofluorescence microscopy demonstrated that these complexes accumulated in neurons with a striking decrease in free ubiquitin levels. Exogenous ubiquitin restored p53 degradation to extracts from injured neurons confirming that Mdm2 function was intact. Finally, antisense-mediated downregulation of ubiquitin in cultured hippocampal neurons resulted in p53 and Mdm2 accumulation as well as apoptotic death. These results point to a novel mechanism to stabilize p53 and promote neuronal cell death in the central nervous system.

Animals↗

PubMed2001

Increased expression of Fas (CD95/APO-1) in adult rat brain after kainate-induced seizures.

Fas (CD95/APO-1), a transmembrane glycoprotein and receptor for the Fas ligand, plays an important role in apoptosis. The present study examined whether excitotoxic cell death induces Fas expression in the adult rat brain. Although relatively light immunostaining was observed in control brain sections, significantly increased Fas immunoreactivity was seen from 4 h to 5 days after the onset of kainic acid-induced seizures. Increased expression of both Fas mRNA and protein were also evident by reverse transcription polymerase chain reaction and Western blotting, respectively. Fas induction was correlated with neuronal apoptosis as demonstrated by colocalization of Fas and terminal dT-mediated dUTP nick end-labeling (TUNEL). Cells with increased Fas-expression were also immunoreactive for tumor suppressor p53 and neuronal specific nuclear protein (NeuN). These results suggest that Fas receptor may contribute to excitotoxic neuronal death in cooperation with p53, and further implicates the Fas pathway in the pathophysiology of neurodegenerative diseases.

Animals↗

PubMed2001

An analysis of relationships among plant community phenology and seasonal metrics of Normalized Difference Vegetation Index in the northern part of the monsoon region of China.

This study focuses on relationships between the phenological growing season of plant communities and the seasonal metrics of Normalized Difference Vegetation Index (NDVI) at sample stations and pixels overlying them, and explores the procedure for determining the growing season of terrestrial vegetation at the regional scale, using threshold NDVI values obtained by surface-satellite analysis at individual stations/pixels. The cumulative frequency of phenophases has been calculated for each plant community and each year in order to determine the growing season at the three sample stations from 1982 to 1993. The precise thresholds were arbitrarily set as the dates on which the phenological cumulative frequency reached 5% and 10% (for the beginning) and 90% and 95% (for the end). The beginning and end dates of the growing season were then applied each year as time thresholds, to determine the corresponding 10-day peak greenness values from NDVI curves for 8-km2 pixels overlying the phenological stations. According to a trend analysis, a lengthening of the growing seasons and an increase of the integrated growing season NDVI have been detected in the central part of the research region. The correlation between the beginning dates of the growing season and the corresponding threshold NDVI values is very low, which indicates that the satellite-sensor-derived greenness is independent of the beginning time of the growing season of local plant communities. Other than in spring, the correlation between the end dates of the growing season and the corresponding threshold NDVI values is highly significant. The negative correlation shows that the earlier the growing season terminates, the larger the corresponding threshold NDVI value, and vice versa. In order to estimate the beginning and end dates of the growing season using the threshold NDVI values at sites without phenological data from 1982 to 1993, we calculated the spatial correlation coefficients between NDVI time-series at each sample station and other contiguous sites year by year. The results provide the spatial extrapolation area of the growing season for each sample station. Thus, we can use the threshold NDVI value obtained at one sample station/pixel for a year to determine the growing season at the extrapolation sites with a similar vegetation type for the same year.

China↗

PubMed2001

Glutamate induced modulation of free Ca(2+) in isolated inner hair cells of the guinea pig cochlea.

To explore the possible involvement of glutamate (Glu) in modulation of inner hair cell (IHC) functions, the glutamate (Glu) induced changes in intracellular free Ca(2+) ([Ca(2+)]i) concentration in isolated IHCs and outer hair cells (OHCs) of the guinea pig cochlea were investigated with fluo-3, a fluorescent probe for intracellular Ca(2+). Their unique flask shape identified the IHCs with a distinct neck and spherical base with a large spherical nucleus. Normal cell shapes could be maintained for about 2 h. Fluorescence of fluo-3 was distributed in the whole isolated IHC with brighter staining nuclei. Static [Ca(2+)]i remained constant within the observation period in the absence of Glu. In the presence of a low concentration of Glu (3.85 microM), there was an increase of [Ca(2+)]i in IHCs, whereas no obvious [Ca(2+)]i change was found in OHCs. The increase of the fluorescence in IHCs reached peak level at 180 s and then gradually reduced at 400 s after the administration of Glu. The increases of [Ca(2+)]i were observed in nine of 10 IHCs, but one IHC did not show any change. For 10 of the observed OHCs, seven showed no [Ca(2+)]i change, and three showed minor reduction of [Ca(2+)]i. The increase of the Glu concentration resulted in a corresponding change of [Ca(2+)]i in the IHCs after three times administration of Glu. These results suggest that Glu acts on the IHCs presynaptic autoreceptor in a positive feedback manner.

Animals↗

PubMed2001

Simulated shortening of proliferation-restricting telomeres during clonal proliferation and senescence of human cells.

In the absence of telomerase or other mechanisms to maintain their length, telomeres in human cells shorten at each round of cell division. This has been suggested to ultimately cause cell cycle exit when a critical telomere length is reached, leading to replicative senescence of the cell. At present, it is not clear whether the division potential of human cells is limited by the overall shortening of telomeres at all chromosomes or the shortening of specific telomeres on certain particular chromosomes. By computer simulations, my previous work has suggested that if the telomere theory is correct, the shortening of only a few, most likely two, telomeres might be preferentially involved in restricting the division of human cells. In this work, the length dynamics of individual telomeres in simulated cell clones were examined over their life span. It is shown that if the shortening of only two telomeres is responsible for restricting the proliferation of a cell, these two specific telomeres will shorten at different rates and have different length distributions from those of the rest telomeres. The unique pattern of length dynamics associated with the proliferation-restricting telomeres (PRT) provides a possibility of experimentally identifying these particular telomeres in human cells.

Cell Division↗

PubMed2001

Telomeres at the chromosome X(p) might be critical in limiting the proliferative potential of human cells.

Normal human somatic cells can only divide for a limited number of times. This phenomenon has been regarded as a reflection of individual aging at the cellular level. Experimental evidences suggest that a cell's division potential is limited by the physical length of telomeres that gradually shorten through successive cell divisions. At present, it is not clear whether such a limit is imposed by the overall shortening of all telomeres or the shortening of certain critical ones. Computer simulations have suggested that among the 92 telomeres in human cells, two specific telomeres might be preferentially involved in such process. Recent experiment has shown that in a culture of male human cells, the length of the telomeres at the chromosome X(p) is reserved over the later passages during clonal proliferation. This unique feature, if can be further confirmed in other cells, implies a critical role of the telomeres at X(p) in limiting the proliferation capacity of human cells.

Cell Division↗

PubMed2001

Mutations in IHH, encoding Indian hedgehog, cause brachydactyly type A-1.

Brachydactyly type A-1 (BDA-1; MIM 112500) is characterized by shortening or missing of the middle phalanges (Fig. 1a). It was first identified by Farabee in 1903 (ref. 2), is the first recorded example of a human anomaly with Mendelian autosomal-dominant inheritance and, as such, is cited in most genetic and biological textbooks. Here we show that mutations in IHH, which encodes Indian hedgehog, cause BDA-1. We have identified three heterozygous missense mutations in the region encoding the amino-terminal signaling domain in all affected members of three large, unrelated families. The three mutant amino acids, which are conserved across all vertebrates and invertebrates studied so far, are predicted to be adjacent on the surface of IHH.

Amino Acid Substitution↗

PubMed2001

Novel endophytes of rice form a taxonomically distinct subgroup of Serratia marcescens.

Six endophytic strains isolated from surface-sterilized rice roots and stems of different rice varieties grown in the Philippines were characterized. They were analyzed by physiological and biochemical tests, SDS-PAGE of whole-cell protein patterns, DNA-DNA hybridization and 16S rDNA sequencing. SDS-PAGE of whole-cell patterns showed that the six isolates fell into two subgroups which were similar but not identical in protein patterns to S. marcescens. The phylogenetic analysis of 16S rDNA sequences of two representative strains IRBG 500 and IRBG 501 indicated that they were closely related to S. marcescens (more than 99% identity). Physiological and biochemical tests corroborated that the isolates were highly related to each other and to S. marcescens. In cluster analysis, all six isolates were clustered together at 93% similarity level and grouped closely with Serratia marcescens at 86% similarity level. DNA-DNA hybridization studies revealed that the isolates shared high similarity levels with S. marcescens (> or =86% DNA-DNA binding), indicating they belong to the same species. However, the isolates differed in several biochemical characteristics from the type strain. They produce urease and utilize urea and L(+) sorbose as a substrate, which is different from all known Serratia reference strains. These results suggest that the six endophytic isolates represent a novel, non-pigmented subgroup of S. marcescens.

Bacterial Proteins↗

PubMed2001

Branched nanowire based guanine rich oligonucleotides.

Self-assembly and aggregation of guanine rich sequences can provide useful insights into DNA nanotechnology and telomeric structure and function. In this paper, we designed a guanine rich sequence d(GGCGTTTTGCGG). We found that it can form stable structure in appropriate condition and it exhibits an anomalous CD spectra. This structures can be imaged in ambient environment with a Nanoscope III AFM (Digital Instruments). We found it forms branch structure and long multistrand DNA nanowire after incubation at 37 degrees C for 6-12 hours in 25 mM TE (pH=8.0) + 5 mM Mg2+ + 50 mM K+. The ability to self-assemble into branches and long wires not only clearly demonstrate its potential as scaffold structures for nanotechnology, but also give aids to understand telomeric structure further. We have proposed a model to explain how these structures formed.

Circular Dichroism↗

PubMed2001

Specific detection of Bradyrhizobium and Rhizobium strains colonizing rice (Oryza sativa) roots by 16S-23S ribosomal DNA intergenic spacer-targeted PCR.

In addition to forming symbiotic nodules on legumes, rhizobial strains are members of soil or rhizosphere communities or occur as endophytes, e.g., in rice. Two rhizobial strains which have been isolated from root nodules of the aquatic legumes Aeschynomene fluminensis (IRBG271) and Sesbania aculeata (IRBG74) were previously found to promote rice growth. In addition to analyzing their phylogenetic positions, we assessed the suitability of the 16S-23S ribosomal DNA (rDNA) intergenic spacer (IGS) sequences for the differentiation of closely related rhizobial taxa and for the development of PCR protocols allowing the specific detection of strains in the environment. 16S rDNA sequence analysis (sequence identity, 99%) and phylogenetic analysis of IGS sequences showed that strain IRBG271 was related to but distinct from Bradyrhizobium elkanii. Rhizobium sp. (Sesbania) strain IRBG74 was located in the Rhizobium-Agrobacterium cluster as a novel lineage according to phylogenetic 16S rDNA analysis (96.8 to 98.9% sequence identity with Agrobacterium tumefaciens; emended name, Rhizobium radiobacter). Strain IRBG74 harbored four copies of rRNA operons whose IGS sequences varied only slightly (2 to 9 nucleotides). The IGS sequence analyses allowed intraspecies differentiation, especially in the genus Bradyrhizobium, as illustrated here for strains of Bradyrhizobium japonicum, B. elkanii, Bradyrhizobium liaoningense, and Bradyrhizobium sp. (Chamaecytisus) strain BTA-1. It also clearly differentiated fast-growing rhizobial species and strains, albeit with lower statistical significance. Moreover, the high sequence variability allowed the development of highly specific IGS-targeted nested-PCR assays. Strains IRBG74 and IRBG271 were specifically detected in complex DNA mixtures of numerous related bacteria and in the DNA of roots of gnotobiotically cultured or even of soil-grown rice plants after inoculation. Thus, IGS sequence analysis is an attractive technique for both microbial ecology and systematics.

Bradyrhizobium↗

PubMed2001

[Effect of aldosterone on the secretion of endothelin by ventricular fibroblasts].

Using cell culture, radioimmunoassay for endothelin and RT-PCR, the effect of aldosterone on the endothelin secretion of ventricular fibroblasts was studied. The results showed that aldosterone (1 x 10(-7) mol/L) promoted the expression of ppET-1 mRNA, which began to increase in 2 hours and attained the highest level in 4 hours, thereafter decreased; aldosterone increased the endothelin level in ventricular fibroblasts and fibroblast conditioned growth medium (FCGM) as well, which was blocked by spironolactone (1 x 10(-6) mol/L), an aldosterone receptor antagonist. The results suggest that aldosterone can increase endothelin secretion by ventricular fibroblasts, which can be inhibited by its receptor antagonist spironolactone.

Aldosterone↗

PubMed2001

Identification of SNPs in human gamma aminobutyric acid A receptor gamma2 gene.

Gamma aminobutyric acid (GABA) is a major inhibitory neurotransmitter. Because of its importance and diverse functions, studies of single nucleotide polymorphisms in the GABA receptor genes are of great significance, which may produce useful molecular markers for genetic analysis of neurological disease, and possibly lead to the discovery of pathogenic mutations. We identified eleven SNPs in the entire exon regions, immediate intron regions and promoter region of human GABA receptor gamma2 gene by direct sequencing. In this discovery, 2 non-synonymous cSNPs and 1 splicing variant are found.

Evolution, Molecular↗

PubMed2001

Modulation of BmKAS-1 and BmK1-3-2 to sodium channel in rat dorsal root ganglion neurons.

OBJECTIVE: To investigate what effects BmKAS-1 (a polypeptide purified from the Chinese scorpion Buthus martensi Karsch [BmK] and named as BmK activator of skeletal-muscle ryanodine receptor) and its upstream mixture BmK1-3-2 have on Na+ channels in dorsal root ganglion (DRG) small diameter neurons. METHODS: The whole-cell patch-clamp technique was used to investigate the effects of BmKAS-1 and BmK1-3-2 on Na+ current in rat small diameter DRG neurons. RESULTS: About 50% peak Na+ current was suppressed by 10 micrograms/ml of BmK1-3-2. 1.62 micrograms/ml of BmKAS-1 also blocked 50% peak Na+ current, and there was an obvious dose-dependent relationship. CONCLUSION: Both BmK1-3-2 and BmKAS-1 have a blocking effect on Na+ channels, and this may one of the mechanisms for the analgetic effect of BmK1-3-2 and BmKAS-1.

Animals↗