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D Y Chen

Publications and source records attributed to D Y Chen.

At least 55 records · Page 3Linked to original sources
PubMed1996

The role of Ca2+ and protein kinase C in the acrosome reaction of giant panda (Ailuropoda melanoleuca) spermatozoa.

Fresh semen was collected from adult male giant pandas and the role of Ca2+, Ca2+ ionophore A23187 and protein kinase C (PKC) in sperm motility and acrosome reaction (AR) was assessed by lens culinaris agglutinin conjugated with fluorescein isothiocyanate (FITC-LCA) labeling and transmission electron microscopy. The AR in giant panda spermatozoa was characterized by vesiculation of the outer acrosomal membrane through its invagination. Both the sperm motility and the AR rate decreased significantly (p < 0.05) in Ca2+-free and low Ca2+ medium. The addition of 10 microM Ca2+ ionophore A23187 potently stimulated AR. After incubation for capacitation, the PKC activator phorbol 12-myristate 13-acetate (PMA) stimulated AR in a dose-dependent manner and its effect could be overcome by the PKC inhibitor staurosporine. These results suggest that Ca2+ and PKC play an important role in the sperm acrosome reaction of the giant panda.

Journal Article↗
PubMed1996

Nuclear/cytoplasmic localization of the von Hippel-Lindau tumor suppressor gene product is determined by cell density.

The product of the von Hippel-Lindau (VHL) tumor suppressor gene, the gene inactivated in VHL disease and in sporadic clear-cell renal carcinomas, has recently been shown to have as a functional target the transcription elongation complex, elongin (also called SIII). Here it is shown that there is a tightly regulated, cell-density-dependent transport of VHL into and/or out of the nucleus. In densely grown cells, the VHL protein is predominantly in the cytoplasm, whereas in sparse cultures, most of the protein can be detected in the nucleus. We have identified a putative nuclear localization signal in the first 60 and first 28 amino acids of the human and rat VHL protein, respectively. Sequences in the C-terminal region of the VHL protein may also be required for localization to the cytosol. These findings provide the initial indication of a novel cell density-dependent pathway that is responsible for the regulation of VHL cellular localization.

3T3 Cells↗
PubMed1996

XpsD, an outer membrane protein required for protein secretion by Xanthomonas campestris pv. campestris, forms a multimer.

XpsD is an outer membrane lipoprotein, required for the secretion of extracellular enzymes by Xanthomonas campestris pv. campestris. Our previous studies indicated that when the xpsD gene was interrupted by transposon Tn5, extracellular enzymes were accumulated in the periplasm (Hu, N.-T., Hung, M.-N., Chiou, S.-J., Tang, F., Chiang, D.-C. Huang, H.-Y. and Wu, C.-Y. (1992) J. Bacteriol. 174, 2679-2687). In this study, we constructed a series of substitutions and deletion mutant xpsD genes to investigate the roles of NH2- and COOH-terminal halves of XpsD in protein secretory function. Among these secretion defective xpsD mutations, one group (encoded by pCD105, pYLA, pKdA6, and pKD2) caused secretion interference when co-expressed with wild type xpsD, but the other (encoded by pMH7, pKdPs, and pKDT) did not. Cross-linking studies and gel filtration chromatography analysis indicated that the wild type XpsD protein forms a multimer in its native state. Similar gel filtration analysis of xpsD mutants revealed positive correlations between multimer formation and secretion interfering properties exerted by the mutant XpsD proteins in the parental strain XC1701. Those mutant XpsD proteins (encoded by pCD105, pYL4, pKdA6, and pKD2) that caused secretion interference formed multimers that are similar to the wild type XpsD multimers and those (encoded by pMH7, pKdPs, and pKDT) that did not formed smaller ones. Furthermore, gel filtration and anion exchange chromatography analyses indicated that the wild type XpsD protein co-fractionated with XpsD (delta 29-428) or XpsD (delta 448-650) protein but not with XpsD (delta 74-303) or XpsD (delta 553-759) protein. We propose that the mutant XpsD (delta 29-428) protein caused secretion interference primarily by forming mixed nonfunctional multimers with the wild type XpsD protein in XC1701 (pCD105), whereas the mutant XpsD (delta 74-303) did so by competing for unknown factor(s) in XC1701(pYL4).

Bacterial Outer Membrane Proteins↗
PubMed1996

Gel and free solution electrophoresis of variably charged polymers.

To assess the role of charge density on polyelectrolyte mobility, both gel and free solution electrophoresis experiments are performed on poly(acrylic acid) and acrylic acid/acrylamide copolymers. Control of charge density for poly-(acrylic acid) is achieved through solution pH, while control for acrylic acid/ acrylamide copolymers is obtained through chain composition. In either approach, the effective fraction of charged repeat units can be varied from 0 to 100% without a major interruption of solvent quality. Polyelectrolyte mobility in the presence of a monovalent counterion is observed to rise linearly with charge density when this density is low. A transition to charge density independence then occurs over a surprisingly narrow window of charge density. For vinyl polymers of the sort examined here, the transition occurs when 35-40% of the repeat units are charged. These observations are qualitatively consistent with the free solution electrophoresis model proposed by Manning and several previous data sets. An unexpected overlap of normalized gel and free solution data reveals that the charge density exerts a comparable influence in either environment. Results from the present study help define the experimental conditions in which electrophoresis can provide polymer separation by charge density and those in which the method can provide polymer separation by molecular weight.

Acrylates↗
PubMed1996

Role of central mu, delta-1, and kappa-1 opioid receptors in opioid-induced muscle rigidity in the rat.

BACKGROUND: Opioids appear to produce their physiologic effects by binding to at least three types of opioid receptors, the mu (mu), delta (delta), and kappa (kappa) receptors. Muscle rigidity occurs after administration of supra-analgesic doses of potent mu-preferring agonists like alfentanil. The role of different supraspinal opioid receptors in this rigidity has been addressed only recently. To elucidate the contribution of central mu, delta, and kappa receptors to muscle rigidity, the effects of intracerebroventricularly administered opioid receptor-selective agonists and antagonists on alfentanil-induced muscle rigidity were examined in rats. METHODS: Rats in which chronic intracerebroventricular cannulae had been implanted received an intracerebroventricular infusion of either saline or a mu (D-Ala2,N-Me-Phe4-Gly5-olenkephalin; DAMGO), delta(1) (D-Pen2,D-Pen5-enkephalin; DPDPE), or kappa(1) (trans-(+/-)-3,4-dichloro-N-methyl-N-(2-(1-pyrrolidinyl)- cyclohexyl)-benzene-acetamide methane sulfonate; U50,488H) opioid agonist. Ten minutes later, they received either saline or the mu-agonist alfentanil subcutaneously. Muscle rigidity was assessed using hindlimb electromyographic activity. Different groups of animals were pretreated with an intracerebroventricular infusion of either saline or a mu (D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH2; CTAP), delta (naltrindole), or kappa(1) (norbinaltorphimine) opioid antagonist before administration of either saline or a selective intracerebroventricular agonist. RESULTS: The mu agonist DAMGO alone dose-dependently induced muscle rigidity. This effect was antagonized by pretreatment with the mu-selective antagonist CTAP. Neither DPDPE nor U50,488H, when administered alone, affected muscle tone. However, both the delta(1) and kappa(1) agonists dose-dependently attenuated alfentanil-induced rigidity. This antagonism of alfentanil rigidity was abolished after pretreatment with the delta (naltrindole) and kappa(1) (nor-binaltorphimine) antagonists, respectively. CONCLUSIONS: The present data demonstrate that whereas systemic opiate-induced muscle rigidity is primarily due to the activation of central mu receptors, supraspinal delta(1) and kappa(1) receptors may attenuate this effect. This finding is consistent with previous demonstrations of functional interactions between different central opioid receptor populations in other opiate effects, and could have important pharmacotherapeutic implications.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗
PubMed1996

Patterns of contrast enhancement in the pediatric spine at MR imaging with single- and triple-dose gadolinium.

PURPOSE: To assess patterns of nerve root and spinal cord contrast enhancement in the pediatric spine at magnetic resonance (MR) imaging with single- and triple-dose gadolinium. MATERIALS AND METHODS: In three control patients with no suspected pathologic spinal condition and 19 patients with a suspected condition, spinal cords were evaluated prospectively for potential spread of tumor to cerebrospinal fluid ("drop metastases") (n = 18) or Guillain-Barré syndrome (n = 1). After enhancement with 0.1 mmol/kg gadolinium, patients without definite drop metastases (n = 8) received a booster of 0.2 mmol/kg gadolinium 30-40 minutes later; clinical follow-up was obtained 12 1/2 to 19 months later. RESULTS: Drop metastases appeared as nodular areas of enhancement in 11 patients. Vascular enhancement related to the spinal cord surface and emerging nerve roots was observed in images obtained in all control patients, as well as in patients with negative findings at lumbar puncture and at clinical or MR imaging follow-up examination (n = 6). Vascular and nerve root enhancement increased with triple-dose gadolinium and was greater in patients after radiation therapy (n = 17) than in control patients (n = 3). CONCLUSION: Use of triple-dose gadolinium did not result in detection of additional cases of drop metastases.

Adolescent↗
PubMed1996

[Calcium distribution changes during epididymal maturation of mouse and guinea pig sperms].

Calcium was localized by in situ precipitation with potassium antimonate during epididymal maturation of the mouse and guinea pig sperms. In caput epididymis the calcium in mouse sperm head was mainly localized on the inner surface of tha outer acrosomal membrane (OAM) in preacrosomal region. During the passage from the caput epididymis to the cauda epididymis the calcium amount of mouse sperm did not undergo apparent changes. In comparison with mouse sperm, there were a few fine calcium deposite granules on the inner surface of the guinea pig sperm OAM on the abdomen side at the caput epididymis stage, but these granules disappeared at the cauda epididymis stage. The microvilli of columnar cell in columnar epithlium lining the epididymal duct are probably involved in regultion of Ca2+ concentration of the intraluminal fluid. The calcium precipitation granules distributing in the microvilli were observed. An abundance of Ca2+ were present in the intraluminal fluid of the corpus epididymis and they might have some important functions during the process of sperm maturation. Calcium in sperm tail was mainly distributed in the mitochondria. Compared with the mouse sperm, the mitochondria of guinea pig sperm possessed more calcium.

Animals↗
PubMed1995

Inhibition of transcription elongation by the VHL tumor suppressor protein.

Germline mutations in the von Hippel-Lindau tumor suppressor gene (VHL) predispose individuals to a variety of tumors, including renal carcinoma, hemangioblastoma of the central nervous system, and pheochromocytoma. Here, a cellular transcription factor, Elongin (SIII), is identified as a functional target of the VHL protein. Elongin (SIII) is a heterotrimer consisting of a transcriptionally active subunit (A) and two regulatory subunits (B and C) that activate transcription elongation by RNA polymerase II. The VHL protein was shown to bind tightly and specifically to the Elongin B and C subunits and to inhibit Elongin (SIII) transcriptional activity in vitro. These findings reveal a potentially important transcriptional regulatory network in which the VHL protein may play a key role.

Amino Acid Sequence↗
PubMed1995

Characterization of the VHL tumor suppressor gene product: localization, complex formation, and the effect of natural inactivating mutations.

The human VHL tumor suppressor gene has been implicated in the inherited disorder von Hippel-Lindau disease and in sporadic renal carcinoma. The homologous rat gene encodes a 185-amino acid protein that is 88% sequence identical to the aligned 213-amino acid human VHL gene product. When expressed in COS-7 cells, both the human and the rat VHL proteins showed predominant nuclear, nuclear and cytosolic, or predominant cytosolic VHL staining by immunofluorescence. A complicated pattern of cellular proteins was seen that could be specifically coimmunoprecipitated with the introduced VHL protein. A complex containing VHL and proteins of apparent molecular masses 16 and 9 kDa was the most consistently observed. Certain naturally occurring VHL missense mutations demonstrated either complete or partial loss of the p16-p9 complex. Thus, the VHL tumor suppressor gene product is a nuclear protein, perhaps capable of specifically translocating between the nucleus and the cytosol. It is likely that VHL executes its functions via formation of specific multiprotein complexes. Identification of these VHL-associated proteins will likely clarify the physiology of this tumor suppressor gene.

Amino Acid Sequence↗
PubMed1995

A role for CNS alpha-2 adrenergic receptors in opiate-induced muscle rigidity in the rat.

A number of potential neurochemical mediators of opiate-induced muscle rigidity have been proposed based on the results of systemic drug studies and on knowledge of the brain sites implicated in opiate rigidity. The effects of i.c.v. pretreatment with selected opioidergic, alpha adrenergic and serotonergic drugs on muscle rigidity induced with systemic injection of the potent opiate agonist alfentanil (ALF) were investigated in spontaneously ventilating rats. The opiate antagonist methylnaloxonium (MN; 0.2-14 nmol), alpha-2 adrenergic agonists dexmedetomidine (DEX; 0.4-42 nmol) or 2-(2,6-diethylphenylamino)-2-imidazoline hydrochloride (ST91; 4-400 nmol), alpha-1 adrenergic antagonist prazosin (PRZ; 7-70 nmol) or serotonergic antagonist ketanserin (KET; 18-550 nmol) were injected i.c.v. (10 microliters) and ALF (500 micrograms/kg s.c.) was administered 10 min later. S.c. electrodes were used to record gastrocnemius electromyographic activity. Both MN and DEX dose-dependently and potently antagonized ALF-induced rigidity. ST91 produced shorter-lived, less profound, antagonism of ALF rigidity. PRZ, at the highest dose tested, produced a delayed and modest reduction in ALF rigidity. A large, non-selective, dose of KET incompletely attenuated ALF rigidity. These results lend support to the hypothesis that central opioid and alpha-2 adrenergic receptors mediate opiate-induced muscle rigidity in the rat.

Adrenergic alpha-Agonists↗
PubMed1995

Suspected multiple sclerosis: MR imaging with a thin-section fast FLAIR pulse sequence.

PURPOSE: To compare thin-section, sagittal, fast fluid-attenuated inversion-recovery (FLAIR) magnetic resonance (MR) imaging with conventional axial spin-echo (SE) imaging for early detection of multiple sclerosis (MS) in the brain. MATERIALS AND METHODS: Conventional 5-mm axial proton-density- and T2-weighted SE images and sagittal 2-mm fast FLAIR images of the brain in five healthy volunteers and 25 patients with clinically suspected MS were evaluated and graded as normal or as showing possible or probable MS in a double-blind study. RESULTS: Fast FLAIR was judged better than SE in 37% of cases, equal to SE in 63%, and never worse than SE. In 43% of patients considered to have normal SE images, fast FLAIR images showed abnormalities consistent with MS. A subependymal striated appearance observed in several cases is believed to represent early inflammation and/or demyelination around subependymal veins in MS. CONCLUSION: Sagittal thin-section fast FLAIR is superior to conventional axial proton-density- and T2-weighted SE pulse sequences for detection of MS plaques in the brain.

Adult↗
PubMed1994

Separation of fragments up to 570 bases in length by use of 6% T non-cross-linked polyacrylamide for DNA sequencing in capillary electrophoresis.

Non-cross-linked polyacrylamide is a very convenient medium for the separation of DNA sequencing fragments in capillary electrophoresis. We demonstrate DNA sequencing with this matrix at an electric field of 200 V/cm and at room temperature. Resolution is observed to decrease exponentially with fragment length. Fragments 570 bases in length generate a resolution of 0.5, which is adequate for sequence identification.

Cross-Linking Reagents↗
PubMed1994

High-speed and high-accuracy DNA sequencing by capillary gel electrophoresis in a simple, low cost instrument. Two-color peak-height encoded sequencing at 40 degrees C.

A low-cost DNA sequencer was constructed based on a single helium-neon laser. The two-color peak-height encoded sequencing protocol, based on the use of T7 DNA polymerase in a manganese buffer, was used to generate samples. Two termination reactions were performed. In the first, a TAMRA (applied Biosystems)-labeled primer was extended in the presence of ddATP and ddCTP. The amounts of dideoxynucleotides were adjusted to produce a 3:1 peak height ratio. Similarly, a ROX (Applied Biosystems)-labeled primer was extended in the presence of ddGTP and ddTTP; the amounts of dideoxynucleotides was adjusted to produce a 3:1 peak height ratio. The pooled fragments were separated on a 4% T LongRanger gel operated at 39 degrees C. Over 500 bases of sequence were generated in 50 min.

Capillary Action↗
PubMed1994

Activation energy of single-stranded DNA moving through cross-linked polyacrylamide gels at 300 V/cm. Effect of temperature on sequencing rate in high-electric-field capillary gel electrophoresis.

In DNA sequencing, single-stranded DNA fragments are separated by gel electrophoresis. This separation is based on a sieving mechanism where DNA fragments are retarded as they pass through pores in the gel. In this paper, we present the mobility of DNA sequencing fragments as a function of temperature; mobility is determined in 4% T LongRanger gels at an electric field of 300 V/cm. The temperature dependence is compared with the predictions of the biased reptation model. The model predicts that the fragment length for the onset of biased reptation with stretching increases with the square of temperature; the data show that the onset of biased reptation with stretching decreases with temperature. Biased reptation fails to model accurately the temperature dependence of mobility. We analyzed the data and extracted the activation energy for passage of sequencing fragments through the gel. For fragments containing less than ca. 200 bases, the activation energy increases linearly with the number of bases at a rate of 25 J/mol per base; for longer fragments, the activation energy increases at a rate of 6.5 J/mol per base. This transition in the activation energy presumably reflects a change in conformation of the DNA fragments; small fragments exist in a random coil configuration and larger fragments migrate in an elongated configuration.

Chemical Phenomena↗
PubMed1994

Yoctomole detection limit by laser-induced fluorescence in capillary electrophoresis.

Laser-induced fluorescence detection in a sheath flow cuvette is the most sensitive method of detecting fluorescent molecules for capillary electrophoresis. This manuscript demonstrates the detection of 50 yoctomoles (1 yoctomole = 1 ymol = 1 x 10(-24) mol) of rhodamine 6G. A 1-mW He-Ne laser (lambda = 543.5 nm) was used as the excitation source. This detection limit is a 10 times improvement compared to the previous state-of-the-art detection limit in separation science.

Coloring Agents↗
PubMed1994

[Analytical study on processing of Scutellaria baicalensis Georyl by HPLC].

This paper deal with the effect of processing on Scutellaria baicalensis. A HPLC method for the determination of baicalin in the drug processed in four different ways has been established. The method is simple, specific and accurate. The recovery is 99.5% and relative standard deviation 0.99%.

Chromatography, High Pressure Liquid↗