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Biomedical subjects

C Shi

Publications and source records attributed to C Shi.

31 records · Page 2Linked to original sources
PubMed1994

Regeneration of HoxD expression domains during pattern regulation in chick wing buds.

The expression domains of genes located at the 5' end of the HoxD (formerly Hox-4) complex appear to correlate with pattern along both the proximal-distal (PrDi) and the anterior-posterior (AP) axes of the developing limb bud, and it has been suggested that the HoxD gene products are involved in the specification of positional information during limb development. The apical ectodermal ridge is required for limb outgrowth and is thought to influence mesodermal cells at the distal end of the limb bud in a region within which patterning events occur. In this paper, we examine the expression of 5' HoxD genes during PrDi pattern regulation in chick wing buds. In limbs undergoing pattern regulation, we demonstrate that the domains of HoxD11 and HoxD13 gene expression are "regenerated" within 24 hr of removal of the distal mesenchyme. In contrast, in limbs which will not form distal structures, HoxD13 expression becomes reduced.

Animals↗
PubMed1994

Resistance of human immunodeficiency virus type 1 to acyclic 6-phenylselenenyl- and 6-phenylthiopyrimidines.

Acyclic 6-phenylselenenyl- and 6-phenylthiopyrimidine derivatives are potent and specific inhibitors of human immunodeficiency virus type 1 (HIV-1). The development of in vitro resistance to two derivatives, 5-ethyl-1-(ethoxymethyl)-(6-phenylthio)-uracil (E-EPU), was evaluated by serial passage of HIV-1 in increasing concentrations of inhibitor. HIV-1 variants exhibiting > 500-fold resistance to E-EPSeU and E-EPU were isolated after sequential passage in 1, 5, and 10 microM inhibitor. The resistant variants exhibited coresistance to related acyclic 6-substituted pyrimidines and the HIV-1-specific inhibitors (+)-(5S)-4,5,6,7-tetrahydro-5- pyrimidines and the HIV-1-specific inhibitors (+)-(5S)-4,5,6,7-tetrahydro-5- methyl-6-(3-methyl-2-butenyl)imidazo[4,5,1-jk]benzodiazepin-2(1H)- thione (TIBO R82150) and nevirapine, but remained susceptible to 3'-azido-3'-deoxythymidine, 2',3'-dideoxycytidine, 2',3'-dideoxyinosine, and phosphonoformic acid. DNA sequence analysis of reverse transcriptase (RT) derived from E-EPSeU-resistant virus identified a Tyr (TAT)-to-Cys (TGT) mutation at either codon 188 (Cys-188; 9 of 15 clones) or codon 181 (Cys-181; 5 of 15 clones). The same amino acid changes were found in RT from E-EPU-resistant virus, but the Cys-181 mutation was more common (9 of 10 clones) than the Cys-188 mutation (1 of 10 clones). Site-specific mutagenesis and production of mutant recombinant viruses demonstrated that both the Cys-181 and Cys-188 mutations cause resistance to E-EPSeU and E-EPU. Of the two mutations, the Cys-188 substitution produced greater E-EPSeU and E-EPU resistance. The predominance of the Cys-188 mutation in E-EPSeU-resistant variants has not been noted for other classes of HIV-1 specific RT inhibitors. HIV-1 resistance is likely to limit the therapeutic efficacy of acyclic 6-substituted pyrimidines if they are used as monotherapy.

Antiviral Agents↗
PubMed1994

Murine model of accelerated transplant arteriosclerosis.

To define the role of specific gene deletions and mutations in the development of transplant arteriosclerosis, we generated an accelerated model of the disease in mice. Carotid arteries were transplanted between B.10A(2R) (H-2h2) donor mice and C57BL/6J (H-2b) recipients and compared with arteries isografted between H-2b mice. Immunosuppressive drugs were not used. Within 7 days, the allografted carotid artery formed a neointima composed of mononuclear leukocytes (CD45+) that were predominantly monocytes or macrophages (ie, CD11b+ cells with single-lobed nuclei). CD4+ and CD8+ cells were present as well. By 30 days, the neointima became exuberant, and mononuclear leukocytes were largely replaced by smooth muscle cells. Cells staining for proliferating-cell nuclear antigen were abundantly present in the intima at both early and late time points, indicating the proliferation of mononuclear leukocytes and smooth muscle cells. The area of the intima increased from day 7 to day 30 (P < .0005), as did the number of nuclei (P = .0005), but the density of the nuclei decreased (P = .02), suggesting the formation of extracellular matrix. Six of the eight isografts formed no neointima, and in samples from the remaining two, a single layer of smooth muscle neointimal cells covered just a portion of the vessel circumference. This model, which reproduces many of the features of human transplant arteriosclerosis but at an accelerated pace, should prove useful for determining the roles in transplant arteriosclerosis of genes that code for components of immunologic and inflammatory responses.

Animals↗
PubMed1994

[The upstream sequence of cholera toxin B subunit gene: effect on CTB expression].

In this work, we have studied the effect of cholera toxin A structure gene on the expression of the distal ctxB gene by the methods of deletion and frame-shift mutation. The results showed that: The expression level of Plasmid pUC19CTB, which was constructed by cloning the XbaI-EcoRI restriction fragment into pUC19 and ctxA gene was out-frame with lacZ' gene, is about 30 micrograms/ml; If a frame shift mutation was introduced at XbaI site of pUC19CTB so that the cholera toxin A gene was inframe with lacZ' and could be translated, the expression level of ctxB was decreased to 12 micrograms/ml; When A further deletion from XbaI to ClaI of cholera toxin A gene (about 550bp) was made and ctxA was outframe with LacZ', ctxB expression was decreased two fold compared to pUC19CTB; If the ctxA was inframe with LacZ' so ctxA gene could be translated, the expression level of CTB is much lower than the plasmid outframe with lacZ'. These observations could not be explained by the current knowledge about genetical regulation of cholera toxin operon. The promoter we found located in the cholera toxin A subunit gene, which is responsible for the expression of cholera toxin B subunit, may answer the question why the 550bp non-coding sequence could enhance the expression of cholera toxin B subunit.

Base Sequence↗
PubMed1994

[Cloning and screening on tumor-related genes inactivated in rat hepatoma cells].

The paper describes an experiment screening tumor-related genes which specifically expressed in rat normal liver cells but inactivated in hepatoma cells with subtractive hybridization technique. During the test, subtracting normal liver cDNA with hepatoma mRNA produces probe-A whereas subtracting hepatoma cDNA by normal liver mRNA gives probe-B. The paper shows six cDNA fragments (TR 1-6) which hybridize probe-A preferentially obtained through dot-blot screening of 2500 colonies with the two probes. Among TR 1-6, special expressions of TR 2 and TR 4 in normal liver cells are further analyzed.

Animals↗
PubMed1993

Combination of intracellular staining of retrogradely labeled neurons and anterograde fluorescent tracing: use of the confocal laser scanning microscope.

This report describes a combined retrograde tracing, intracellular injection and anterograde fluorescence labeling method using the application of confocal laser scanning microscopy. By simultaneously viewing the morphology of identified projection neurons and the distribution of anterogradely labeled fibers and terminals, this approach allows accurate characterization of the anatomical relationships between these two elements. To demonstrate this approach, the retrograde tracer Fast Blue was injected into the bed nucleus of stria terminalis (BNST) and the anterograde tracer tetramethylrhodamine-conjugated dextran was injected into the insular cortex in adult rats. After one week survival time, the brains were fixed and sectioned on a vibratome. Individual BNST projecting neurons identified in the amygdaloid complex on 120 microns thick sections were intracellularly injected with Lucifer Yellow under visual control and analyzed with confocal laser scanning microscopy. The results demonstrate that images from very thin optical sections can clearly show potential synaptic contacts between anterograde labeling and intracellularly labeled projecting neurons. Stacked images from optical sections show, in very great detail, the morphology of projection neurons in three-dimensions. Compared to other methodological combinations, the present method provides a more simple and efficient means to trace three successive components of a putative neuron chain.

Amidines↗
PubMed1992

Pore formation and mitogenicity in blood cells by the class 2 protein of Neisseria meningitidis.

The class 2 outer membrane protein (MIEP) of Neisseria meningitidis has recently been shown to be mitogenic for lymphocytes (Liu, M.A., Friedman, A., Tai, J., Martinez, D., Deck, R. R., Hawe, L. A., Shieh, J. T.-C., Jenkins, T. D., Donnelly, J. J., and Oliff, A. I. (1992) Proc. Natl. Acad. Sci. U.S.A. 89, 4633-4637. In this study, a possible connection between MIEP's mitogenicity and its possible action as a porin was investigated. MIEP, purified from the bacterial outer membrane protein complex under denaturing conditions, caused a modest but specific release of ions (86Rb) from both erythrocytes and lymphocytes, ultimately resulting in cell lysis. The dose-response of MIEP on erythrocyte lysis was qualitatively similar to a known porin (protein I from Neisseria gonorrhoeae) but was much less efficient. Induction or preservation of native structure in MIEP increased pore formation, resulting in levels comparable to that of the protein I porin. These observations suggest that native MIEP, free of the other outer membrane proteins of Neisseria meningitidis, can efficiently form pores in cells, but that denatured MIEP is variably and marginally effective. However, pore formation by MIEP was not related to its mitogenicity in lymphocytes, based on: (i) native MIEP was not mitogenic; (ii) denatured MIEP was highly mitogenic; and (iii) denatured MIEP was mitogenic at concentrations below the threshold level for pore formation. Therefore, mitogenicity is dependent upon MIEP being in a denatured, monomeric state and is masked by native conformation.

Bacterial Outer Membrane Proteins↗
PubMed1992

Position-specific growth of mouse limb bud cells in vitro.

The relationship between cellular position and growth control has been studied in cultures of dissociated fragments of mouse limb bud cells. Using cells derived from various positions along the anterior-posterior axis of the limb bud we have developed culture conditions that optimize growth of positionally isolated cells. Under these conditions limb bud cells display an inherent, position-specific growth response; proliferation of cells derived from anterior and central regions of the limb is enhanced over that of posterior derived cells. Thus, within the total population of limb bud cells the in vitro growth of posterior cells is unique and correlates with the positional activity associated with the zone of polarizing activity. Anterior and posterior cells were cocultured to determine whether interactions between these two groups of positionally distinct cells lead to the stimulation of growth that has been observed in vivo. We observe a slight but consistent position-dependent stimulation of growth that is indicative of a mitogenic signal passing between these positionally disparate cells. Similarities between position-related growth dynamics in vivo and in vitro suggest that positional interactions that are important for limb formation can occur between dissociated cells cultured under standard conditions.

Animals↗
PubMed1991

[Various methods of processing pyritum].

Five methods of processing pyritum and the effect of temperature fluctuations on processed products were studied using Fe2+ in the decoction, sulphur in processed products and sulphur separated out of processed products after adding hydrochloric acid as indexes. The results may serve as a reference for further study on pyritum.

Hot Temperature↗
PubMed1990

[Inhibitory effect of yunfujing on vestibular stimulative response in rats and volunteers].

Fifty female rats were used in the experiment. With rotation model, Yunfujing was shown to inhibit nystagmic response of rats. The inhibitory effect was 20-30 times stronger than that of Mihuanjun. In Coriolis test, the tolerance time of vestibular stimulative response was taken as a parameter for judging drug efficacy in 32 male volunteers. Following oral administration of Yunfujing at a dose of 400 mg, the tolerance time of vestibular stimulative response was prolonged significantly from 411.34 to 759.63 s. In the mean time, no changes of blood pressure and pulse were observed in the treated group.

Adolescent↗
PubMed1988

Altered plasma membrane ion permeability in mercury-induced cell injury: studies in hepatocytes of elasmobranch Raja erinacea.

The effects of HgCl2, CH3HgCl, p-chloromercuribenzene sulfonate (PCMBS), and CdCl2 on plasma membrane and cell metabolic functions of skate (Raja erinacea) hepatocytes in suspension culture were assessed by measuring (a) the rates of Na+-dependent and -independent L-[14C]alanine uptake, (b) Na+-dependent 86Rb+ uptake, a measure of Na-K-ATPase activity, (c) 86Rb+ efflux, a measure of K+ permeability, (d) the difference between the 3H2O and [14C]inulin distribution spaces, a measure of intracellular water volume, (e) cellular ATP concentrations, and (f) glutathione (GSH) and glutathione disulfide (GSSG) levels. The initial rates of L-alanine and 86Rb+ uptake were inhibited by each of these metals in the following order: HgCl2 greater than CH3HgCl greater than PCMBS greater than CdCl2. Inorganic mercury significantly inhibited the initial rates of Na+-dependent L-alanine and 86Rb uptakes at a concentration of 10 microM, whereas 100 microM produced nearly complete inhibition. These effects were dose-dependent, immediate (observed after less than 5 min of incubation with the metal), and persistent. Mercuric chloride also impaired volume regulatory mechanisms in skate hepatocytes: cells treated with 50 microM HgCl2 swelled slowly over a 60-min interval to volumes nearly double those of control cells. In addition, HgCl2 prevented the normal volume regulatory decrease observed after swelling the hepatocytes in hypotonic media. Mercuric chloride (5-50 microM) produced a rapid initial loss of a large fraction of intracellular 86Rb, followed by a slower rate of release of the remaining isotope. These effects were prevented if GSH was added with, but not following HgCl2. In contrast, dithiothreitol, a more permeable thiol, both prevented and even partially reversed the effects of mercury. Mercuric chloride (10 microM) had no effect on cellular ATP, GSH, or GSSG levels for up to 4 hr incubation. These findings indicate that 86Rb+ (K+) efflux is a sensitive indicator of mercury toxicity, and are consistent with the hypothesis that the plasma membrane is a primary target for mercury's effects. A change in membrane permeability to K+ would dissipate transmembrane electrochemical gradients, and may contribute to the apparent inhibition of transport processes energized by these gradients, such as Na+-alanine cotransport, and volume regulatory mechanisms.

Alanine↗
PubMedDate not supplied

Inhibition of DNA synthesis and oncogene expression in tumor cells by the biological factor DIF.

A regulatory factor isolated from the maternal part of bovine placentas (decidua inhibitory factor, DIF) inhibits the incorporation of thymidine into the DNA of a variety of animal and human tumors. The degree of inhibition is dependent on the concentration of the factor. Results indicate that signal transduction occurs via a Ca2+ mobilizing pathway after specific binding of the inhibitor to tumor cell surface receptors. On of the main consequences of DIF action is the inhibition of c-fos and c-myc expression and/or degradation.

Animals↗