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Z Dai

Publications and source records attributed to Z Dai.

At least 109 records · Page 6Linked to original sources
PubMed1993

A role of tyrosine phosphorylation in the formation of acetylcholine receptor clusters induced by electric fields in cultured Xenopus muscle cells.

During the development of the neuromuscular junction, acetylcholine receptors (AChRs) become clustered in the postsynaptic membrane in response to innervation. In vitro, several non-neuronal stimuli can also induce the formation of AChR clusters. DC electric field (E field) is one of them. When cultured Xenopus muscle cells are exposed to an E field of 5-10 V/cm, AChRs become clustered along the cathode-facing edge of the cells within 2 h. Recent studies have suggested the involvement of tyrosine kinase activation in the action of several AChR clustering stimuli, including nerve, polymer beads, and agrin. We thus examined the role of tyrosine phosphorylation in E field-induced AChR clustering. An antibody against phosphotyrosine (PY) was used to examine the localization of PY-containing proteins in E field-treated muscle cells. We found that anti-PY staining was colocalized with AChR clusters along the cathodal edge of the cells. In fact, cathodal PY staining could be detected before the first appearance of AChR clusters. When cultures were subjected to E fields in the presence of a tyrosine kinase inhibitor, tyrphostin RG-50864, cathodal AChR clustering was abolished with a half maximal inhibitory dosage of 50 microM. An inactive form of tyrphostin (RG-50862) had no effect on the field-induced clustering. These data suggest that the activation of tyrosine kinases is an essential step in E field-induced AChR clustering. Thus, the actions of several disparate stimuli for AChR clustering seem to converge to a common signal transduction mechanism based on tyrosine phosphorylation at the molecular level.

Animals↗
PubMed1993

Clustering of the acetylcholine receptor by the 43-kD protein: involvement of the zinc finger domain.

A postsynaptic membrane-associated protein of M(r) 43,000 (43-kD protein) is involved in clustering of the nicotinic acetylcholine receptor (AChR) at the neuromuscular junction. Previous studies have shown that recombinant mouse 43-kD protein forms membrane-associated clusters when expressed in Xenopus oocytes. Coexpression with the AChR results in colocalization of the receptor with the 43-kD protein clusters (Froehner, S. C., C. W. Luetje, P. B. Scotland, and J. Patrick, 1990. Neuron. 5:403-410). To understand the mechanism of this clustering, we have studied the role of the carboxy-terminal region of the 43-kD protein. The amino acid sequence of this region predicts two tandem zinc finger structures followed by a serine phosphorylation site. Both Torpedo 43-kD protein and the carboxy-terminal region of the mouse 43-kD protein bind radioisotopic zinc. Mutation of two histidine residues in this predicted domain greatly attenuates zinc binding, lending support to the proposal that this region forms zinc fingers. When expressed in oocytes, the ability of this mutant 43-kD protein to form clusters is greatly reduced. Its ability to interact with AChR, however, is retained. In contrast, a mutation that eliminates the potential serine phosphorylation site has no effect on clustering of the 43-kD protein or on interaction with the AChR. These findings suggest that protein interactions via the zinc finger domain of the 43-kD protein may be important for AChR clustering at the synapse.

Amino Acid Sequence↗
PubMed1993

Synthesis and regulation of insulin-like growth factor binding protein-5 in FRTL-5 cells.

FRTL-5 cells, a diploid nontransformed line of rat thyroid follicular cells, exhibit a marked mitogenic response to insulin-like growth factors (IGFs) when they are exposed to TSH. Because IGF binding proteins (IGFBPs) are important modulators of IGF actions, we investigated the capacity of FRTL-5 cells to synthesize IGFBPs. We found that FRTL-5 cell conditioned media contained a single band of approximately 31 kilodaltons on ligand blot analysis. This band represents IGFBP-5 because: 1) it can be immunostained with a specific antibody raised against human IGFBP-5; 2) by Northern analysis, total RNA from FRTL-5 cells contains a major 6-kilobase transcript when hybridized with a cDNA for rat IGFBP-5; and 3) no transcripts were observed when Northern blots of FRTL-5 cells were hybridized with complementary DNAs for rat IGFBP-1, -2, -3, -4 or -6. Conditioned media IGFBP-5 increased in response to IGF-I, IGF-II, and insulin in a dose-dependent fashion, compared with unstimulated FRTL-5 cells. At maximally effective concentrations IGF-I was 3.5- and 6-fold more potent than IGF-II and insulin, respectively. The addition of a monoclonal antibody (Sm 1.2) to IGF-I completely inhibited IGF-I stimulation of the IGFBP-5 6-kilobase transcript and the appearance of IGFBP-5 in FRTL-5 conditioned media. Stimulation of IGFBP-5 synthesis by the IGFs and insulin appeared to be regulated at the messenger RNA (mRNA) level, because each stimulated similar increases in both IGFBP-5 mRNA and media protein at maximally effective concentrations. TSH, on the other hand, inhibited basal levels of IGFBP-5 mRNA and attenuated the increase in IGFBP-5 mRNA stimulated by IGF-I. FRTL-5 cells provide a relatively uncomplicated model to study the regulation and action of IGFBP-5 and the mechanisms by which IGFs interact with this binding protein.

Animals↗
PubMed1993

[Treatment of blepharospasm and hemifacial spasm with botulinum A toxin].

112 patients with blepharospasm or hemifacial spasm were satisfactorily treated by local injections of small doses of botulinum A toxin, resulting in rapid relief or alleviation of the symptoms. No systemic adverse reactions were noted, and local side effects were minor and transient. The study shows that the therapy is safe and effective as a simple and easy alternative of surgical intervention.

Adult↗
PubMed1993

[Portal angiography and color Doppler for portal hemodynamics research].

The portal developing rates of 0%, 10%, 35% and 55% in portal hypertension were detected by prostaglandin E1(PGE1) indirect portal digital subtraction angiography (DSA). The rates of left gastric vein (LGV), short gastric vein (SGV), umbilical vein (UV) and spontaneous splenorenal Vein shunt collateral were 80%, 45%, 25% and 5% respectively and the confluent point of LGV was shown directly. Time--density curve depict showed that the hepatofugal blood flow rates of the main portal vein and splenic vein were 10% and 15% respectively. Color Doppler showed not only the imageology of the portal system, but the blood flow. The developing rates of LGV, SGV, UV and spontaneous splenorenal vein shunt collateral were 80%, 5%, 10% and 85% respectively. Following the improvement of portal developing grades, the main portal vein flow, splenic vein flow, and superior mesenteric vein flow were decreased. The results indicates the more poorly hepatopetal flow irrigation, the more intensive condition in high hemodynamics of the portal system.

Adult↗
PubMed1992

Interaction of secreted insulin-like growth factor-I (IGF-I) with cell surface receptors is the dominant mechanism of IGF-I's autocrine actions.

In a prior report we presented evidence that insulin-like growth factor-I (IGF-I) can act in an autocrine fashion by demonstrating that FRTL-5 cells transfected with hIGF-IA fusion genes express and secrete biologically active IGF-I that renders the stimulation of DNA synthesis in FRTL-5 cells independent of their requirement for exogenous IGFs or insulin. To determine if IGF-I's autocrine actions require secretion or can be mediated by interactions with intracellular receptors, we have created a new line of FRTL-5 cells that express a mutant IGF-IA precursor containing the endoplasmic reticulum retention amino acid sequence, Lys-Asp-Glu-Leu (KDEL), at its carboxyl terminus. The mutant IGF-IA/KDEL precursor expressed by stably transfected FRTL-5 cells was shown to be retained intracellularly and to have biological activity comparable with mature IGF-I, as judged by the activity of partially purified IGF-IA/KDEL in wild type FRTL-5 cells. Expression of IGF-IA/KDEL in FRTL-5 cells, however, neither augmented TSH-stimulated DNA synthesis nor stimulated IGF-binding protein-5 expression, as does IGF-IA expression in transfected FRTL-5 cells and the addition of exogenous IGF-I to wild type FRTL-5 cells. IGF-IA/KDEL expression, however, desensitized FRTL-5 cells to the actions of exogenous IGF-I despite having only minimal effects on cell surface type I receptor number, suggesting that intracellular IGF-I is capable of significant biological actions. The failure of IGF-IA/KDEL to replicate the actions of secreted IGF-I, taken together with the findings that a monoclonal antibody against IGF-I blocked IGF-I's actions in IGF-I-secreting transfected FRTL-5 cells, provides evidence that IGF-I secretion and interaction with cell surface type I IGF receptors is the dominant mechanism of IGF-I's autocrine actions.

Amino Acid Sequence↗
PubMed1992

The influence of basic fibroblast growth factor on acetylcholine receptors in cultured muscle cells.

Acetylcholine receptors (AChRs) in Xenopus muscle cells undergo changes in channel kinetics during development in culture and these changes are somehow related to innervation. Recently we showed that basic fibroblast growth factor (bFGF), when locally applied, can mimic the effect of nerve in inducing a postsynaptic-type development. In this study, we examined whether bFGF can influence the developmental changes of AChRs. Patch clamp method was employed to record single AChR channel currents from cultured Xenopus myotomal muscle cells and the kinetics of low-conductance AChR channels were analyzed. In cultures treated with 1 microgram/ml bFGF at an early stage (stage 23), the burst duration of low-conductance AChR channels showed a 1.5-fold decrease between the first and second day in culture, while it underwent a remarkable 3-fold decrease during the same period in the control. Histogram analyses showed that the low-conductance channels were composed of a fast and a slow component and that the decrease in burst duration was due to a shift in the population from the slow to the fast. bFGF treatment appeared to slow down this shift by retaining the slow channels for a longer period of time. This effect is probably not due to channel modulation as the burst duration of short channel in older cells (stage 40) was not affected by bFGF. These data suggest that bFGF may enhance the metabolic stability of intrinsically short-lived AChRs. This effect seems to parallel the stabilization of junctional AChRs at the innervated endplate. Thus, bFGF, or a related polypeptide growth factor, may mediate this and other innervation-induced changes in the postsynaptic membrane.

Animals↗
PubMed1992

Base sequence criteria and Cartesian coordinates for stable B/Z and B/Z/B junctions in relaxed DNA.

It seems increasingly evident that if the Z form of DNA exists in the genome it must exist as short sections of alternating pyrimidine-purine sequences in the midst of very long sections of B-form DNA. We have determined the minimum length of a string of alternating CG base pairs that can go into the Z form in the middle of a long B form. Self-complimentary oligomers of the form T(M)(CG)(N)A(M) were synthesized. The conformation of the resulting duplex was determined in 6M aqueous NaCl solution by Raman scattering. We have found that 12 alternating CG base pairs is the minimum length required to form a stable Z form of DNA inside of a long B form section. Only the 4 center CG base pairs go into the Z form. These 4 CG base pairs in the Z form are flanked on each side by 4 CG base pairs in a non-Z (probably B) form as well as the ..TT.. ..AA.. sequences in the B form. We propose a model of the B/Z junction in which the double helix flips directly from the B form to the Z form so that there are no base pairs in the junction. In this model the B form is nucleated in the AT base pairs on each end and is propagated into the CG base pairs in the center. This model is supported by isotopic H/D exchange experiments that shows that the H/D exchange of the non-Z form CG base pairs is highly retarded and indicates that they remain in the B form. A Thermodynamic analysis of the concentration dependence of the melting point of the duplexes in both low and high salt, supports our model and rules out the possibility of hairpin formation. The enthalpy for the formation of a B/Z junction is determined to be about +16 kcal/junction. A comparison of these results with recent results on B/Z junctions in super-coiled DNA is given. Molecular modeling calculations permit us to obtain values for the coordinates and torsional angles of the oligomers showing both B/Z and B/Z/B junctions. The Cartesian coordinates for these oligomers as well as stereo figures of these models in color are available from the authors.

Base Sequence↗
PubMed1992

Expression of maize phosphoenolpyruvate carboxylase in transgenic tobacco : effects on biochemistry and physiology.

The expression of maize (Zea mays) phophoenolpyruvate carboxylase (PPC) gene constructions was studied in transgenic tobacco plants (Nicotiana tabacum). Where transcription was under the control of a maize PPC gene promoter, a low level of aberrantly large PPC transcript was detected. Analysis of this PPC transcript indicated that transcription initiation occurs upstream of the normal site. Despite the aberrant transcription initiation, expression of the PPC transcript was still light-regulated. Higher levels of maize PPC transcript of the correct size were obtained with a chimeric gene construction containing a tobacco (Nicotiana plumbaginifolia) chlorophyll a/b binding protein gene promoter. The PPC activities in the leaves of these transgenic plants were up to twofold higher than those of nontransformed plants. Two forms of PPC with different kinetic properties were identified in leaf extracts of the transgenic plants: one form with a high apparent K(m) for phosphoenolpyruvate (maize isozyme), and a second form exhibiting a low apparent K(m) (tobacco isozyme). Biochemical analyses of these plants indicated that the transgenic plants had significantly elevated levels of titratable acidity and malic acid. These biochemical differences did not produce any significant physiological changes with respect to photosynthetic rate or CO(2) compensation point.

Journal Article↗
PubMed1992

Control of Photosynthesis and Stomatal Conductance in Ricinus communis L. (Castor Bean) by Leaf to Air Vapor Pressure Deficit.

Castor bean (Ricinus communis L.) has a high photosynthetic capacity under high humidity and a pronounced sensitivity of photosynthesis to high water vapor pressure deficit (VPD). The sensitivity of photosynthesis to varying VPD was analyzed by measuring CO(2) assimilation, stomatal conductance (g(s)), quantum yield of photosystem II (phi(II)), and nonphotochemical quenching of chlorophyll fluorescence (q(N)) under different VPD. Under both medium (1000) and high (1800 micromoles quanta per square meter per second) light intensities, CO(2) assimilation decreased as the VPD between the leaf and the air around the leaf increased. The g(s) initially dropped rapidly with increasing VPD and then showed a slower decrease above a VPD of 10 to 20 millibars. Over a temperature range from 20 to 40 degrees C, CO(2) assimilation and g(s) were inhibited by high VPD (20 millibars). However, the rate of transpiration increased with increasing temperature at either low or high VPD due to an increase in g(s). The relative inhibition of photosynthesis under photorespiring (atmospheric levels of CO(2) and O(2)) versus nonphotorespiring (700 microbars CO(2) and 2% O(2)) conditions was greater under high VPD (30 millibars) than under low VPD (3 millibars). Also, with increasing light intensity the relative inhibition of photosynthesis by O(2) increased under high VPD, but decreased under low VPD. The effect of high VPD on photosynthesis under various conditions could not be totally accounted for by the decrease in the intercellular CO(2) in the leaf (C(i)) where C(i) was estimated from gas exchange measurements. However, estimates of C(i) from measurements of phi(II) and q(N) suggest that the decrease in photosynthesis and increase in photorespiration under high VPD can be totally accounted for by stomatal closure and a decrease in C(i). The results also suggest that nonuniform closure of stomata may occur in well-watered plants under high VPD, causing overestimates in the calculation of C(i) from gas exchange measurements. Under low VPD, 30 degrees C, high light, and saturating CO(2), castor bean (C(3) tropical shrub) has a rate of photosynthesis (61 micromoles CO(2) per square meter per second) that is about 50% higher than that of tobacco (C(3)) or maize (C(4)) under the same conditions. The chlorophyll content, total soluble protein, and ribulose-1,5-bisphosphate carboxylase/oxygenase level on a leaf area basis were much higher in castor bean than in maize or tobacco, which accounts for its high rates of photosynthesis under low VPD.

Journal Article↗
PubMed1992

Creation of an autocrine model of insulin-like growth factor-I action in transfected FRTL-5 cells.

Although there is much evidence that insulin-like growth factor-I (IGF-I) is delivered to its target tissues via the circulation from distal sites of synthesis, many other observations suggest that it is synthesized in or near its target tissues and acts by autocrine and/or paracrine modalities. Studies of the mechanisms of such local actions, however, have been problematic, because in vivo studies of a single tissue are technically difficult and confounded by many variables, whereas in vitro studies of autocrine/paracrine actions have been limited by low levels of IGF-I expression and/or lack of dramatic or clearly defined responses to IGF-I. We, therefore, set about to create IGF-I expression in FRTL-5 cells, a diploid nontransformed line of rat thyroid follicular cells that have been extensively studied as a model of TSH action. The modest increase in thymidine incorporation stimulated by TSH in wild type FRTL-5 cells is markedly increased in the presence of exogenous IGF-I. By transfecting these cells with a chimeric IGF-IA gene, driven either by the mouse metallothionein-1 or IGF-II 5' genomic regulatory regions, we were able to generate stable cell lines that synthesize and secrete mature IGF-I. This was demonstrated by RIA, by Northern analysis, and by polyacrylamide gel electrophoresis characterization of the radiolabeled intracellular and extracellular products that reacted with an IGF-I antibody. The mitogenic responses to TSH in IGF-I-expressing transfected FRTL-5 cells were indistinguishable from those stimulated by TSH and IGF-I in wild type or control-transfected cells (FRTL-5 cells stably transfected with a similar transgene that does not encode IGF-I). Basal DNA synthesis was higher and the peak of thymidine incorporation was earlier in IGF-I-expressing transfected FRTL-5 cells than in wild type or control cells (18-24 h vs. 30-36 h). The concentrations of TSH that maximally stimulate the incorporation of thymidine were not altered by IGF-I expression, and transfected cells did not appear to be transformed, as judged by their inability to form colonies in soft agar. TSH-stimulated DNA synthesis was blocked in IGF-I-expressing FRTL-5 cell by a monoclonal antibody to IGF (Sm 1.2). Thus, secretion of IGF-I appears to be required for the autocrine effects observed. These IGF-I-expressing FRTL-5 cell lines provide a model in vitro system to study the intracellular processing of IGF-I and the mechanisms by which IGF-I acts in an autocrine manner.

Animals↗
PubMed1992

Treatment of blepharospasm, hemifacial spasm and strabismus with botulinum a toxin.

Thirty patients with blepharospasm, hemifacial spasm, strabismus and entropion were treated with botulinum A toxin giving satisfactory results. Rapid spasm relief, correction of strabismus and entropion were obtained. Only mild, transient and local side-effects occurred. The patients were followed up for 4-12 weeks with no recurrence. The clinical results show that local injection of a minute dose of botulinum A toxin in treating blepharospasm, hemifacial spasm, strabismus and entropion is a safe, effective and simple method of nonsurgical therapy.

Adult↗
PubMed1991

Photosynthetic and photorespiratory characteristics of flaveria species.

The genus Flaveria shows evidence of evolution in the mechanism of photosynthesis as its 21 species include C(3), C(3)-C(4), C(4)-like, and C(4) plants. In this study, several physiological and biochemical parameters of photosynthesis and photorespiration were measured in 18 Flaveria species representing all the photosynthetic types. The 10 species classified as C(3)-C(4) intermediates showed an inverse continuum in level of photorespiration and development of the C(4) syndrome. This ranges from F. sonorensis with relatively high apparent photorespiration and lacking C(4) photosynthesis to F. Among the intermediates, the photosynthetic CO(2) compensation points at 30 degrees C and 1150 micromoles quanta per square meter per second varied from 9 to 29 microbars. The values for the three C(4)-like species varied from 3 to 6 microbars, similar to those measured for the C(4) species. The activities of the photorespiratory enzymes glycolate oxidase, hydroxypyruvate reductase, and serine hydroxymethyltransferase decreased progressively from C(3) to C(3)-C(4) to C(4)-like and C(4) species. On the other hand, most intermediates had higher levels of phosphenolpyruvate carboxylase and NADP-malic enzyme than C(3) species, but generally lower activities compared to C(4)-like and C(4) species. The levels of these C(4) enzymes are correlated with the degree of C(4) photosynthesis, based on the initial products of photosynthesis. Another indication of development of the C(4) syndrome in C(3)-C(4)Flaveria species was their intermediate chlorophyll a/b ratios. The chlorophyll a/b ratios of the various Flaveria species are highly correlated with the degree of C(4) photosynthesis suggesting that the photochemical machinery is progressively altered during evolution in order to meet the specific energy requirements for operating the C(4) pathway. In the progression from C(3) to C(4) species in Flaveria, the CO(2) compensation point decreased more rapidly than did the decrease in O(2) inhibition of photosynthesis or the increase in the degree of C(4) photosynthesis. These results suggest that the reduction in photorespiration during evolution occurred initially by refixation of photorespired CO(2) and prior to substantive reduction in O(2) inhibition and development of the C(4) syndrome. However, further reduction in O(2) inhibition in some intermediates and C(4)-like species is considered primarily due to the development of the C(4) syndrome. Thus, the evolution of C(3)-C(4) intermediate photosynthesis likely occurred in response to environmental conditions which limit the intercellular CO(2) concentration first via refixation of photorespired CO(2), followed by development of the C(4) syndrome.

Journal Article↗
PubMed1991

[Immunohistochemical observation of ANP in rhesus monkey heart and lung].

Rabbit anti-human atriopeptin serum and the peroxidase anti-peroxidase (PAP) immunohistochemical technique were used to study atrial natriuretic polypeptide (ANP) in the heart and lung of rhesus monkeys. ANP-like active substance was found in atrial myocardium cells and in bronchial epithelial cells as well as in some cells of the alveolar septum. The substance appeared as brown particulates mainly located in the cytoplasm around the nucleus, mostly at opposite poles of the nucleus. The nature of these particulates will be determined.

Animals↗