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S Chen

Publications and source records attributed to S Chen.

At least 433 records · Page 24Linked to original sources
PubMed2000

Identification of a novel WD repeat-containing gene predominantly expressed in developing and regenerating neurons.

In the present study, we have identified a novel gene, NDRP (for neuronal differentiation-related protein), which is predominantly expressed in developing and regenerating neurons. The predicted NDRP comprises 1,019 amino acid residues and has 6 WD repeats in the N-terminal half and multiple potential nuclear localization signals (NLSs) at the C-terminal part. This molecule shows no significant structural similarity with any other molecules in available databases. In situ hybridization and immunohistochemistry revealed the highest expression of NRDP in sensory neurons, for instance, olfactory epithelia and neural layer of retina during embryonic development, as well as in perinatal dorsal root ganglions. The expression of this gene in intact motor neurons such as in the hypoglossal nerve was undetectable but became obvious after axotomy. These results suggest that the product of this gene might be involved in the development of sensory neurons as well as the regeneration of motor neurons.

Amino Acid Sequence↗
PubMed2000

The urine/plasma electrolyte ratio: a predictive guide to water restriction.

Patients with hypotonic hyponatremia are encountered commonly in the general practice of medicine. Nearly all strategies for the management of subacute or chronic hyponatremia call for some amount of water restriction. The considerations for such a prescription have not been addressed in the literature. We describe therefore a simple approach grounded in the physiology of electrolyte-free water clearance that can be used at the bedside.

Electrolytes↗
PubMed2000

Controlling hamiltonian chaos by adaptive integrable mode coupling

The adaptive integrable mode coupling method is proposed to control two-dimensional Hamiltonian chaos. We demonstrate that this control method can stabilize chaotic motions into regular ones in a model of the standard map. Global stochasticity can be removed from the phase space by the control being switched on and off.

Journal Article↗
PubMed2000

Temperature-dependent function of the glutamine phosphoribosylpyrophosphate amidotransferase ammonia channel and coupling with glycinamide ribonucleotide synthetase in a hyperthermophile.

Genes encoding glutamine phosphoribosylpyrophosphate amidotransferase (GPAT) and glycinamide ribonucleotide synthetase (GARS) from Aquifex aeolicus were expressed in Escherichia coli, and the enzymes were purified to near homogeneity. Both enzymes were maximally active at a temperature of at least 90 degrees C, with half-lives of 65 min for GPAT and 60 h for GARS at 80 degrees C. GPAT activity is known to depend upon channeling of NH(3) from a site in an N-terminal glutaminase domain to a distal phosphoribosylpyrophosphate site in a C-terminal domain where synthesis of phosphoribosylamine (PRA) takes place. The efficiency of channeling of NH(3) for synthesis of PRA was found to increase from 34% at 37 degrees C to a maximum of 84% at 80 degrees C. The mechanism for transfer of PRA to GARS is not established, but diffusion between enzymes as a free intermediate appears unlikely based on a calculated PRA half-life of approximately 0.6 s at 90 degrees C. Evidence was obtained for coupling between GPAT and GARS for PRA transfer. The coupling was temperature dependent, exhibiting a transition between 37 and 50 degrees C, and remained relatively constant up to 90 degrees C. The calculated PRA chemical half-life, however, decreased by a factor of 20 over this temperature range. These results provide evidence that coupling involves direct PRA transfer through GPAT-GARS interaction rather than free diffusion.

Adenine Nucleotides↗
PubMed2000

Identification by 16S rRNA gene analyses of a potential novel mycobacterial species as an etiological agent of canine leproid granuloma syndrome.

PCR amplifications of the 16S rRNA gene were performed on 46 specimens obtained from 43 dogs with canine leproid granuloma syndrome to help determine its etiology. Sequence capture PCR was applied to 37 paraffin-embedded specimens from 37 dogs, and nested PCR was attempted on DNA from 9 fresh tissue specimens derived from 3 of the 37 aforementioned dogs and from an additional 6 dogs. Molecular analyses of the paraffin-embedded tissues and fresh tissue specimen analyses were performed at separate institutions. PCR products with identical sequences over a 350-bp region encompassing variable regions 2 and 3 of the 16S rRNA gene were obtained from 4 of 37 paraffin-embedded specimens and from all 9 specimens of fresh tissue originating from 12 of the 43 dogs. Identical sequences were determined from amplicons obtained from paraffin-embedded and fresh specimens from one dog. The consensus DNA sequence, amplified from paraffin-embedded tissue and represented by GenBank accession no. AF144747, shared highest nucleotide identity (99.4% over 519 bp) with mycobacterial strain IWGMT 90413 but did not correspond exactly to any EMBL or GenBank database sequence. With a probe derived from the V2 region of the novel canine sequence, reverse cross blot hybridization identified an additional four paraffin-embedded specimens containing the same novel sequence. In total, molecular methodologies identified the proposed novel mycobacterial sequence in 16 of 43 dogs with canine leproid granuloma syndrome, indicating that the species represented by this sequence may be the principal etiological agent of canine leproid granuloma syndrome.

Animals↗
PubMed2000

Assessment of Chlamydia trachomatis prevalence by PCR and LCR in women presenting for termination of pregnancy.

OBJECTIVES: To determine the prevalence of Chlamydia trachomatis in a patient population presenting for legal termination of pregnancy by polymerase chain reaction (PCR) and ligase chain reaction (LCR), from first catch urine and self administered tampons, and comparing with the traditionally collected endocervical swab tested by both PCR and culture. METHODS: Consecutive women attending for legal termination of pregnancy were screened for chlamydia by patient collected first catch urine and tampon, and physician collected endocervical swab. RESULTS: Of 1175 patients with complete samples, there were 33 (2.8%) in whom chlamydia was detected by two or more assays from one or more sample site. Chlamydia was detected equally well by both PCR and LCR in first catch urine (p = 0.25), tampon (p = 0.5), and endocervical swab (p = 0.5). However, both PCR and LCR were significantly better than culture of an endocervical swab (p = 0.0005) for detection of C trachomatis. CONCLUSION: The prevalence of chlamydia in patients presenting for termination of pregnancy was 2.8%. A simple efficient way of performing screening for chlamydia for women presenting for termination of pregnancy is by first catch urine or tampon, which can be tested by the highly sensitive amplification assays, PCR or LCR.

Abortion, Legal↗
PubMed2000

Angiotensin IV-mediated pulmonary artery vasorelaxation is due to endothelial intracellular calcium release.

Angiotensin (ANG) IV stimulation of pulmonary artery (PA) endothelial cells (PAECs) but not of PA smooth muscle cells (PASMCs) resulted in significant increased production of cGMP in PASMCs. ANG IV receptors are not present in PASMCs, and PASMC nitric oxide synthase activity was not altered by ANG IV. ANG IV caused a dose-dependent vasodilation of U-46619-precontracted endothelium-intact but not endothelium-denuded PAs, and this response was blocked by the ANG IV receptor antagonist divalinal ANG IV but not by ANG II type 1 and 2 receptor blockers. ANG IV receptor-mediated increased intracellular Ca(2+) concentration ([Ca(2+)](i)) release from intracellular stores in PAECs was blocked by divalinal ANG IV as well as by the G protein, phospholipase C, and phosphoinositide (PI) 3-kinase inhibitors guanosine 5'-O-(2-thiodiphosphate), U-73122, and LY-294002, respectively, and was regulated by both PI 3-kinase- and ryanodine-sensitive Ca(2+) stores. Basal and ANG IV-mediated vasorelaxation of endothelium-denuded PAs was restored by exogenous PAECs but not by exogenous PAECs pretreated with the intracellular Ca(2+) chelator 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-AM. These results demonstrate that ANG IV-mediated vasodilation of PAs is endothelium dependent and regulated by [Ca(2+)](i) release through receptor-coupled G protein-phospholipase C-PI 3-kinase signaling mechanisms.

Angiotensin II↗
PubMed2000

Blocking adenylyl cyclase inhibits olfactory generator currents induced by "IP(3)-odors".

Vertebrate olfactory receptor neurons (ORNs) transduce odor stimuli into electrical signals by means of an adenylyl cyclase/cAMP second messenger cascade, but it remains widely debated whether this cAMP cascade mediates transduction for all odorants or only certain odor classes. To address this problem, we have analyzed the generator currents induced by odors that failed to produce cAMP in previous biochemical assays but instead produced IP(3) ("IP(3)-odors"). We show that in single salamander ORNs, sensory responses to "cAMP-odors" and IP(3)-odors are not mutually exclusive but coexist in the same cells. The currents induced by IP(3)-odors exhibit identical biophysical properties as those induced by cAMP odors or direct activation of the cAMP cascade. By disrupting adenylyl cyclase to block cAMP formation using two potent antagonists of adenylyl cyclase, SQ22536 and MDL12330A, we show that this molecular step is necessary for the transduction of both odor classes. To assess whether these results are also applicable to mammals, we examine the electrophysiological responses to IP(3)-odors in intact mouse main olfactory epithelium (MOE) by recording field potentials. The results show that inhibition of adenylyl cyclase prevents EOG responses to both odor classes in mouse MOE, even when "hot spots" with heightened sensitivity to IP(3)-odors are examined.

1-Methyl-3-isobutylxanthine↗
PubMed2000

Regulation of aromatase expression in human ovarian surface epithelial cells.

Ovarian cancer originates mainly from surface epithelial cells, which are potential targets of estrogen action. Using immunohistochemistry and RT-PCR analysis, aromatase (estrogen synthetase) can be detected in human ovarian surface epithelial tumors. In this study, we functionally characterized the aromatase expressed in a primary cell culture, normal human ovarian surface epithelial (HOSE) 17. The apparent K(m) and V(max) values were determined to be 5.8 +/- 0.5 nM, and 0.3 +/- 0.0 pmol/mg.h, respectively. The aromatase activity in HOSE 17 cells can be induced effectively by phorbol esters and forskolin, suggesting that estrogen biosynthesis in HOSE 17 cells is mainly regulated through protein kinase C- and protein kinase A-mediated mechanisms. Exon I-specific RT-PCR revealed that phorbol esters predominantly up-regulated promoter II. Whereas forskolin treatment increased exon I.3A-containing messenger RNA, the aromatase activity remained low in the cells treated with this agent. In vitro transcription/translation analysis using plasmids containing T7 promoter and the human snail gene (SnaH) as a reporter capped with different untranslated exon Is revealed that exon PII-containing transcripts were translated more effectively than exon I. 3-containing transcripts. These findings explain why aromatase activity is higher in cells with the PII-containing transcripts than is cells with the I.3-containing transcripts. Our results indicate that aromatase is functionally expressed in human ovarian surface epithelial cells and its expression is regulated at both the transcriptional and translational levels.

5' Untranslated Regions↗
PubMed2000

PNRC: a proline-rich nuclear receptor coregulatory protein that modulates transcriptional activation of multiple nuclear receptors including orphan receptors SF1 (steroidogenic factor 1) and ERRalpha1 (estrogen related receptor alpha-1).

PNRC (proline-rich nuclear receptor coregulatory protein) was identified using bovine SF1 (steroidogenic factor 1) as the bait in a yeast two-hybrid screening of a human mammary gland cDNA expression library. PNRC is unique in that it has a molecular mass of 35 kDa, significantly smaller than most of the coregulatory proteins reported so far, and it is proline-rich. PNRC's nuclear localization was demonstrated by immunofluorescence and Western blot analyses. In the yeast two-hybrid assays, PNRC interacted with the orphan receptors SF1 and ERRalpha1 in a ligand-independent manner. PNRC was also found to interact with the ligand-binding domains of all the nuclear receptors tested including estrogen receptor (ER), androgen receptor (AR), glucocorticoid receptor (GR), progesterone receptor (PR), thyroid hormone receptor (TR), retinoic acid receptor (RAR), and retinoid X receptor (RXR) in a ligand-dependent manner. Functional AF2 domain is required for nuclear receptors to bind to PNRC. Furthermore, in vitro glutathione-S-transferase pull-down assay was performed to demonstrate a direct contact between PNRC and nuclear receptors such as SF1. Coimmunoprecipitation experiment using Hela cells that express PNRC and ER was performed to confirm the interaction of PNRC and nuclear receptors in vivo in a ligand-dependent manner. PNRC was found to function as a coactivator to enhance the transcriptional activation mediated by SF1, ERR1 (estrogen related receptor alpha-1), PR, and TR. By examining a series of deletion mutants of PNRC using the yeast two-hybrid assay, a 23-amino acid (aa) sequence in the carboxy-terminal region, aa 278-300, was shown to be critical and sufficient for the interaction with nuclear receptors. This region is proline rich and contains a SH3-binding motif, S-D-P-P-S-P-S. Results from the mutagenesis study demonstrated that the two conserved proline (P) residues in this motif are crucial for PNRC to interact with the nuclear receptors. The exact 23-amino acid sequence was also found in another protein isolated from the same yeast two-hybrid screening study. These two proteins belong to a new family of nuclear receptor coregulatory proteins.

Amino Acid Motifs↗
PubMed2000

A novel cyclic adenosine 3',5'-monophosphate-responsive element involved in the transcriptional regulation of the lutropin receptor gene in granulosa cells.

The induction of the lutropin receptor (LHR) in granulosa cells by FSH is mediated, at least in part, by cAMP. However, the classic cAMP-responsive element (CRE) is not present in the 5'-flanking region of the rat LHR gene. Previous studies from our laboratory had shown that three Sp1 sites within the promoter region of the rat LHR (rLHR) bind Sp1 and Sp3 and are involved in the basal and cAMP-mediated transcription of the rLHR gene. In the present studies we show that the rLHR promoter region forms a complex (designated complex A) with nuclear extracts from rat granulosa cells, and the abundance of complex A is markedly increased when using cells that had been pretreated with 8-bromo (Br)-cAMP. We have localized the binding of the protein(s) in complex A to a DNA sequence immediately upstream and partially overlapping with the Sp1c binding site. The core site (designated SAS for Sp1c adjacent sequence) is localized to nucleotide (nt) -146 to -142 and contains the sequence GGGGG. The consensus sequence for the core portion of this element appears to be (G/T)GGGG. Mutations of the SAS site, but not SP1c site, abolish complex A formation. Experiments utilizing rat granulosa cells transfected with luciferase reporter genes driven by the 5'-flanking region of the rLHR gene demonstrate a functional role for the SAS site in the cAMP responsiveness of the rLHR gene.

Animals↗
PubMed2000

The role of the yolk syncytial layer in germ layer patterning in zebrafish.

Formation of the three germ layers requires a series of inductive events during early embryogenesis. Studies in zebrafish indicate that the source of these inductive signals may be the extra-embryonic yolk syncytial layer (YSL). The characterization of genes encoding the nodal-related factor, Squint, and homeodomain protein, Bozozok, both of which are expressed in the YSL, suggested that the YSL has a role in mesendoderm induction. However, these genes, and a second nodal-related factor, cyclops, are also expressed in the overlying marginal blastomeres, raising the possibility that the marginal blastomeres can induce mesendodermal genes independently of the YSL. We have developed a novel technique to study signaling from the YSL in which we specifically eliminate RNAs in the YSL, thus addressing the in vivo requirement of RNA-derived signals from this region in mesendoderm induction. We show that injection of RNase into the yolk cell after the 1K cell stage (3 hours) effectively eliminates YSL transcripts without affecting ubiquitously expressed genes in the blastoderm. We also present data that indicate the stability of existing proteins in the YSL is unaffected by RNase injection. Using this technique, we show that RNA in the YSL is required for the formation of ventrolateral mesendoderm and induction of the nodal-related genes in the ventrolateral marginal blastomeres, revealing the presence of an unidentified inducing signal released from the YSL. We also demonstrate that the dorsal mesoderm can be induced independently of signals from the YSL and present evidence that this is due to the stabilization of (&bgr;)-catenin in the dorsal marginal blastomeres. Our results demonstrate that germ layer formation and patterning in zebrafish uses a combination of YSL-dependent and -independent inductive events.

Animals↗
PubMed2000

Therapeutic potential of endothelin receptor antagonists in diabetes.

Endothelins (ETs) are widely distributed in the body and perform several vascular and non-vascular functions. Experimental evidence indicates that abnormalities of the ET system occur in several organs affected in chronic diabetic complications. Furthermore, ET antagonists were found to prevent structural and functional changes in the target organs of chronic diabetic complications in animal models. Abnormalities of plasma ET levels have also been demonstrated in human diabetes. This review discusses the role of ET in the pathogenesis of chronic diabetic complications. The current experimental evidence suggests that ET antagonism may potentially represent an adjuvant therapeutic tool in the treatment of chronic diabetic complications.

Animals↗
PubMed2000

DNA fingerprinting of Cryptosporidium parvum isolates using amplified fragment length polymorphism (AFLP).

The genetic variability of 10 Cryptosporidium parvum isolates of human and animal origin was investigated using amplified fragment length polymorphism (AFLP). Analysis of fluorescent dye-labeled amplified products was carried out using an ABI PRISMS 377 DNA sequencer and ABI PRISMS GeneScan software. One-hundred and twelve primer combinations were evaluated using a single C. parvum isolate. The patterns generated were highly reproducible. For subsequent study, a subset of 9 primer pairs that yielded 30-90 DNA fragments after the polymerase chain reaction, within the size range of 50-500 bp, was used to screen the 10 C. parvum isolates, including 7 bovine, 1 equine, and 2 of human origin. The animal isolates produced identical fingerprint patterns with every primer combination tested. Of the 2 human isolates tested, 1 of the isolates, passaged in calves, generated the same AFLP DNA banding patterns as the animal isolates, whereas the other isolate, obtained directly from human feces, produced unique patterns. Polymorphism, detected by comparison of the fingerprint patterns of the latter human isolate with the common pattern shared by all other isolates, ranged from 17 to 35% for the 9 primer pairs. The results show that AFLP is a useful method for differentiating C. parvum isolates into 2 distinct genotypes.

Animals↗
PubMed2000

Endothelin receptor blockade prevents augmented extracellular matrix component mRNA expression and capillary basement membrane thickening in the retina of diabetic and galactose-fed rats.

Endothelins (ETs) are a family of vasoactive peptides that have mitogenic properties and have also been associated with altered long-term nuclear signaling. We have previously shown that mRNA levels for ET-1, ET-3, and their receptors are upregulated under hyperhexosemic conditions. In this study, an endothelin antagonist was used to assess the effects of endothelin blockage on the production of two basement membrane transcripts, fibronectin and collagen alpha1 (IV). The microvascular basement membranes were analyzed using ultrastructural morphometry. Streptozotocin-induced diabetic rats, galactose-fed rats (30% galactose in diet), and nondiabetic, non-galactose-fed control rats were studied after 1-month and 6-month follow-up. Simultaneously, similar animal groups were treated with a general ET receptor blocker (bosentan, 100 mg x kg(-1) x day(-1)) and investigated. Semiquantitative reverse transcription-polymerase chain reaction for fibronectin and collagen alpha1 (IV) was conducted after 1 month of follow-up with comparison to beta-actin housekeeping gene using slot blot hybridization and densitometry. Basement membrane thickness was assessed after 6 months of follow-up in diabetic rats, using the orthogonal intercept method. After 1 month of follow-up, increased fibronectin and collagen alpha1 (IV) mRNA were present in the retina of diabetic and galactosemic animals, and the bosentan-treated groups exhibited mRNA levels similar to the control animals. After 6 months of follow-up, diabetes and galactose feeding induced basement membrane thickening, which was partially prevented by bosentan treatment. The above findings indicate that increased production of extracellular matrix proteins leading to thickening of microvascular basement membrane, secondary to hyperhexosemia, may be mediated via augmented ET production.

Animals↗
PubMed2000

Fatigue patterns observed in patients receiving chemotherapy and radiotherapy.

The purpose of this study was to describe the patterns of cancer-related fatigue (CRF) and vigor in patients receiving chemotherapy or radiation therapy. Five studies that measured fatigue and vigor with the Profile of Mood States were used to describe the pattern of CRF and vigor during and after both types of treatment. Repeated-measures ANOVA was used to determine differences over time in each study. Results demonstrate different patterns of CRF for patients receiving chemotherapy and radiation therapy. Chemotherapy-related CRF peaks in the days after chemotherapy, whereas radiation therapy-related CRF gradually accumulates over the course of treatment. The CRF associated with both forms of treatment gradually declines over time. The prevalence, intensity, and persistence of CRF during treatment and for months after treatment is complete make this symptom one that cannot be ignored.

Adolescent↗