Magnetoplasmon emission versus Landau-level scattering in resonant tunneling through double-barrier structures.
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Journal Article↗
Biomedical subjects
C Zhang
Publications and source records attributed to C Zhang.
A triplet of nuclease proteins (NP42-50) is activated in human Jurkat cells undergoing apoptosis.
Activation of a triplet of nuclear proteins (NP42-50) was observed in human Jurkat T cell line following treatment with an antibody to CD95 (Fas/Apo-1), a cell surface molecule involved in apoptotic cell death. The nuclease activity, corresponding to a triplet of proteins observed at approximately 42, 45, and 50 kDa in size, was extractable, heat-stable, and detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis containing deoxyribonucleic acids (SDS-PAGE-DNA) assay. The NP42-50 activity requires the presence of Mg2+/Ca2+ and is insensitive to inactivation by heating at 80 degrees C for 5 min. Zinc effectively inhibited the enzymatic activity of NP42-50 on SDS-PAGE-DNA and also protected Jurkat cells from the CD95-mediated apoptosis in cell cultures. The nuclease activation, however, was not a unique pathway for the CD95-mediated cell death. The apoptosis induced by arabinofuranosyl cytosine, a chemotherapeutic agent, also activated the NP42-50 nuclease activity in Jurkat cells, suggesting that a similar cascade of subsequent events in apoptosis may occur in most instances although many different signals can initiate apoptotic cell death in various cell types. The nuclease identified by this study appears to be distinguishable from DNase I or DNase II by its molecular characteristics and its enzymatic requirements. The NP42-50, with respect to the nuclease activity closely associated with apoptotic cell death, may serve as a candidate for the endonuclease(s) involved in the cleavage of DNA into fragments during apoptosis.
Amino Acid Sequence↗
Inhibition of phage phi 29 assembly by antisense oligonucleotides targeting viral pRNA essential for DNA packaging.
A sensitive and efficient system for the functional assay of antisense oligonucleotides (oligos) was developed based on an in vitro viral assembly system. A 120-base RNA (pRNA), which indispensably participates in bacteriophage phi 29 DNA packaging, was the target for antisense action. Antisense oligos bound to pRNA, as revealed by a slower electrophoretic mobility of pRNA/oligo complexes in comparison with native pRNA. Infectious viruses were assembled in vitro with synthetic pRNA and DNA, as well as with viral proteins produced from cloned genes. Up to 10(7) plaque-forming units per milliliter were obtained in the absence of antisense oligos, while as few as zero plaques were detected in the presence of certain antisense oligos. A 1-base mismatch greatly influenced the inhibitory effect of the antisense oligos, but this 1-based mismatch was not important when the mismatch was placed at the end of the oligo. Five oligos did not bind pRNA or inhibit the assembly of the virion, suggesting that the RNA sequences complementary to these oligos are nonessential or buried internally in the RNA. Viral assembly was strongly inhibited by antisense oligos P15 and P10, targeting either the 5'- or the 3'-end of the pRNA, respectively. Viral assembly was also strongly inhibited by oligo P6, targeting an internal region, residues 75-91, of pRNA. Oligo P6 inhibited DNA packaging activity by blocking the binding of pRNA to the procapsid, while P10 and P15 inhibited DNA packaging activity but did not block the binding of pRNA to the procapsid, suggesting that in addition to the reported internal domain for procapsid binding, pRNA contains another domain at the paired 5'/3'-ends with a yet to be defined role in DNA translocation.
Bacillus Phages↗
Infection and replication of Tat- human immunodeficiency viruses: genetic analyses of LTR and tat mutations in primary and long-term human lymphoid cells.
Tat is an essential regulatory protein for the replication of human immunodeficiency virus (HIV). Mutations in the tat gene have been shown to block HIV replication in human T cells. Several studies have established that Tat releases an elongation block to the transcription of HIV long terminal repeat (LTR); however, it is not known whether this mechanism alone is sufficient to explain the block to HIV replication in human T cells when Tat is absent. It is possible that Tat is also needed for other functions during HIV replication. To test these hypotheses, we studied several tat mutants, including two stop codon mutants and one deletion mutant using replication-competent HIV-1 constructs carrying wild-type or mutant LTRs with modifications in the NF-kappa B and/or Sp1 binding sites. In this study, we show that Tat- HIV-1 with wild-type LTRs can replicate in HeLa cells, and the virus produced from HeLa cells can infect primary peripheral blood lymphocytes and macrophages. It was found that the propagation of the Tat mutants containing wild-type LTRs was less efficient than that of the LTR-modified Tat mutants. Large amounts of viral RNA and particles were synthesized in infections established using the tat mutants that contain modified LTRs. However, this efficient propagation of the LTR-modified tat mutants was restricted to some lymphoid cell lines that have been transformed with other viruses. Thus, despite its essential role for releasing an elongation block, Tat is not otherwise absolutely required for synthesis of full-length HIV transcripts and assembly of virus particles. Direct sequencing of the viral genomes and reinfection kinetics showed no evidence of wild-type reversion even after prolonged infection with the Tat- virus. The implications for in vivo HIV-1 replication and potential application of this system to the study of alternative Tat function are discussed.
Animals↗
Met-enkephalin-like immunoreactivity in microdialysates from nucleus tractus solitarii in piglets during normoxia and hypoxia.
Met-enkephalin-like immunoreactivity in microdialysates from the respiratory-related nucleus tractus solitarii was determined simultaneously with ventilatory responses in seven, spontaneously breathing, developing swine under conditions of normoxia, hypoxia and recovery from hypoxia for 30 min each. Assayed levels of Met-enkephalin-like immunoreactivity in normoxia were 0.89 +/- 0.23 pg/microliters. These levels increased to 203.6 +/- 32.2% and 283.1 +/- 55.8% of control during hypoxia and recovery, respectively. Hyperventilation during hypoxia was not sustained, comprising brief stimulation followed by return to near-control level. Taken together, these results provide further evidence that opioid release may contribute to the suppression of ventilation in hypoxia during development.
Animals↗
Age-related mu-, delta-and kappa-opioid ligands in respiratory-related brain regions of piglets: effect of prenatal cocaine.
Neonates, as compared to older subjects, exhibit increased signs of relative respiratory suppression such as apnea, periodic breathing and only transient hyperventilatory response to hypoxia. Prenatal cocaine exposure exaggerates the respiratory pattern disturbances observed in infants. As endogenous opioids cause central suppression of breathing, we tested their possible involvement in these effects by assessing opioid content in respiratory-related brainstem regions of 2 to 5 (young) and 18 to 22 (older) day-old piglets, unexposed or preexposed to cocaine during 0.66 to 1.0 gestation. The selected ages represent distinct stages in the postnatal development of respiration. beta-Endorphin, methionine-enkephalin, dynorphin A and dynorphin B from the tractus solitarii, ambigualis, gigantoreticularis and parabrachialis medialis nuclei were separated by high performance liquid chromatography, then quantified by radioimmunoassays. Opioid content was higher in the brain regions of the young than of the older piglets, and increased after cocaine exposure in both age groups, but more in the young. These findings support the possible contribution of high opioid content to the relative suppression of respiratory function in early life, and to the exaggerated respiratory dysrhythmia observed in cocaine preexposed neonates.
Aging↗
Mapping of the amino acids in the cytoplasmic loop connecting helices C and D in rhodopsin. Chemical reactivity in the dark state following single cysteine replacements.
The cytoplasmic loop connecting helices C and D in rhodopsin is a part of the region involved in protein-protein interactions during signal transduction. To probe the structure of the CD loop, we have replaced, one at a time, the amino acids 136-150 by cysteine residues. The cysteine substitution mutants contained only the introduced single reactive cysteines and were prepared from a base opsin mutant that retained only the three intradiscal cysteines. All of the cysteine substitution mutants formed the characteristic rhodopsin chromophore (lambda max, 500 nm) with 11-cis-retinal. They showed normal photobleaching characteristics and activated transducin in a light-dependent manner, albeit at lower levels than the wild-type pigment. The newly introduced cysteines in the substitution mutants all underwent alkylation in the dark with the membrane-permeant sulfhydryl reagent N-ethylmaleimide, but with varying rates. The cysteine substitution mutants also showed prominent differences in alkylation with membrane-impermeant N-polymethylenecarboxylmaleimides of various alkyl chain lengths. Notably, derivatization of the cysteines in the mutants was not observed with the polar sulfhydryl reagents iodoacetic acid or iodoacetamide. These findings highlight intrinsic differences in both the reactivity and accessibility of the different cysteine residues in the CD loop and support the important role for a structure in the second cytoplasmic region of rhodopsin.
Amino Acid Sequence↗
The site of the inhibitory action of endogenous opioids in the superior cervical ganglion of the cat.
A low-frequency stimulus train to the preganglionic input inhibits synaptic transmission in the superior cervical ganglion (SCG) of the cat. The inhibition is blocked by naloxone as well as by selective antagonists at mu and delta opiate receptors, which suggests that the mediator is an endogenous opioid [27,29]. Exogenous opioid peptides, including methionine-enkephalin (Met-Enk), which is present in preganglionic axons of the SCG, inhibit ganglionic transmission by a naloxone-sensitive mechanism. In the present study we test, in the anesthetized cat, whether the naloxone-sensitive synaptic inhibition is mediated by a pre- and/or post-synaptic mechanism. As a test of presynaptic inhibition, we measured the acetylcholine (ACh) released by preganglionic stimulation into the venous effluent of the perfused SCG. As a test of post-synaptic inhibition, we measured the effect of a preganglionic conditioning train on the ganglion cell firing evoked by ganglion-stimulant drugs injected into the arterial supply of the ganglion. In presence of naloxone (3 microM), which blocked the synaptic inhibition, the amount of ACh released by stimulated preganglionic axons did not change. Thus, the endogenous opioid which mediates the naloxone-sensitive inhibition does not act by depressing ACh release. In contrast, the ganglion cell firing evoked by ganglion-stimulant drugs was markedly depressed by a conditioning train, and naloxone blocked the depression, which suggests that the endogenous mediator of the naloxone-sensitive inhibition acts postsynaptically to decrease the excitability of ganglion cells. Exogenous Met-Enk depressed both ACh release by preganglionic stimulation and the firing of ganglion cells evoked by ganglion-stimulant drugs.(ABSTRACT TRUNCATED AT 250 WORDS)
Anesthesia↗
Circularly permuted viral pRNA active and specific in the packaging of bacteriophage phi 29 DNA.
A viral-encoded 120-base pRNA has been shown to have an essential role in the packaging of bacteriophage phi 29 DNA. The finding that both the 5'- and 3'-termini of the pRNA are proximate and crucial for biological function (C. Zhang, C. Lee, and P. Guo, 1994, Virology, 201, 77-85) prompted investigation of the activity of circularly permuted pRNAs (cpRNA) and of the expandability and essentiality of bases extending from the termini. A 117-base pRNA with a deletion of three bases downstream of the proximal terminus was active in DNA packaging. Concatemeric DNAs containing two tandem pRNA genes separated by a short or a long loop sequence were constructed. The cpRNAs from these DNA templates were transcribed in vitro and shown to be active in phi 29 DNA packaging, with activity comparable to the parental (noncircularly permuted) pRNA, indicating that neither of the loops tested affected the activity and folding of the cpRNA. As few as four bases were sufficient to serve as a loop for the terminal 180 degree turn, and a loop as long as 27 bases did not affect the cpRNA structure and function. Eight cpRNAs were constructed to assess the effect of openings within the wild-type pRNA structure. Opening of the bulge at residue 38 did not affect cpRNA activity, but opening the bulge at residue 55 greatly reduced it. Although the sequence of the 5',3'-terminal loop was not important for the folding and activity of the cpRNA, the activities of cpRNAs with openings at individual bulges or hairpins were different, indicating that each region plays a different role in pRNA folding and function. Our results indicate that it is possible to generate active circularly permuted pRNA by assigning internal sites of the pRNA as new 3'- and 5'-termini. The creation of new variable ends makes the labeling of internal bases of the pRNA molecule possible and will facilitate the analysis of pRNA secondary and tertiary structure.
Bacillus Phages↗
Involvement of a stem-loop structure in the location of junction sites in viral RNA recombination.
Recombination between RNAs associated with turnip crinkle virus is thought to occur during plus-strand synthesis at motifs resembling the 5'-ends of genomic, subgenomic and satellite RNAs. Common structural regions encompassing the motifs have been found for major crossover sites on two different minus-strand templates, with junctions preferentially located in a single-stranded region at the 3' base of a hairpin. Base changes, deletions and compensatory alteration constructed in and around the hairpin in the region of the turnip crinkle virus genomic RNA involved in recombination support the importance of the hairpin for normal crossover site selection. This region of the genomic RNA is also important for replication of the viral genomic RNA in plants and protoplasts, suggesting a common link between sequences required for recombination and viral replication.
Base Sequence↗
Changes in expression of glutamate receptor subunits following photoreceptor degeneration in the rd mouse retina.
The effects of photoreceptor cell degeneration on the expression of nine alpha-amino-3-hydroxy-5-methyl-isoxasole-4-propionate (AMPA)/kainate glutamate receptor subunit genes were investigated in the rd mouse retina by in situ hybridization. All known AMPA/kainate receptor subunits were found to be expressed in normal mouse retina. Following retinal degeneration, the expression of KA-1 was reduced, that of the GluR7 subunit was greatly increased, and that of the other seven subunits were not significantly affected.
Animals↗
Keratins as markers of differentiated taste cells of the rat.
Cytokeratins in taste buds were immunocytochemically evaluated with monoclonal antibodies. In each of six different epithelial sites in the rat oral cavity, intragemmal cells of taste buds were immunoreactive for keratin polypeptides 8, 18, and 19, as well as for keratin 7, which has not been previously reported in taste buds. Keratin-18-like immunoreactivity was present in fewer than half of the intragemmal cells, whereas all intragemmal cells were immunopositive for keratins 7, 8, and 19. Apart from some salivary duct cells, no other cells in the tongue were immunoreactive for any of these four keratins. Morphological and immunocytochemical profiles indicate that taste buds are islets of simple epithelium embedded in an expanse of stratified squamous epithelium. These simple epithelial cells and their keratins are nerve-dependent, since denervation eliminated all four keratins and replaced elongated taste cells of the vallate papilla with stratified squamous epithelium. We conclude that antibodies against keratins 7, 8, or 19 are useful markers for intragemmal cells in studies of taste bud development, degeneration, regeneration, turnover and tissue culture.
Animals↗
Keratin 18 is associated with a subset of older taste cells in the rat.
All or nearly all intragemmal (elongated) cells of rat taste buds were immunopositive for keratins 7, 8, and 19. In contrast, keratin 18 was detected in 19 +/- 5 cells per taste bud (mean +/- sd), or about 25% of the intragemmal cells. During taste bud development keratins 7, 8, and 19 were evident initially in polygonal cells and later in elongated taste cells. Keratin 8 appeared in vallate taste cells at P0 (postnatal day 0), followed by keratins 7 and 19 at P1, and keratin 18 at P2-P3. Keratin 18 was always limited to elongated cells. The assemblage of elongated taste cells comprising a taste bud began with a single elongated cell, rather than with the synchronous elongation of a cluster of cells. Developmental errors were observed at P2-P3, e.g., some vallate taste cells had a misoriented axis. In order to study the pace of keratin differentiation during cell turnover we injected bromodeoxyuridine (BrdU) into adult rats to monitor taste cell age. Keratin-19-positive intragemmal cells differentiated within 1 day. In contrast, keratin 18 was first detected in cells aged 3 days. Hence, both in taste cell development and replacement, keratin 18 was restricted to the older cells; it was the last taste cell keratin to become expressed during differentiation.
Animals↗
Evolutionary endocrinology of juvenile hormone esterase in Gryllus assimilis: direct and correlated responses to selection.
Hemolymph juvenile hormone esterase (JHE) activity on the third day of the last stadium in the cricket, Gryllus assimilis, exhibited a significant response to selection in each of six replicate lines. Mean realized heritability was 0.26 +/- 0.04. The response was due to changes in whole-organism enzyme activity as well as to changes in the proportion of enzyme allocated to the hemolymph compartment. In vivo juvenile hormone metabolism differed between some lines selected for high vs. low enzyme activity. Only minimal differences were observed between lines with respect to hemolymph protein concentration or whole-cricket activity of juvenile hormone epoxide hydrolase, the other major JH-degrading enzyme. Dramatic correlated responses to selection, equal in magnitude to the direct response, were observed for JHE activity on each of three other days of the last juvenile stadium. In contrast, no correlated responses in JHE activity were observed in adults. This indicates that JHE activities throughout the last stadium will evolve as a highly correlated unit independent of adult activities and the evolution of endocrine mechanisms regulating juvenile development can be decoupled from those controlling adult reproduction. This study represents the first quantitative-genetic analysis of naturally occurring endocrine variation in an insect species.
Age Factors↗
Unusual pattern of mitochondrial DNA deletions in skeletal muscle of an adult human with chronic fatigue syndrome.
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Adult↗
In vitro cerebral vasoactive effects of MK-801.
MK-801, although more consistently neuroprotective in focal ischemia, has had more variable success in the management of global ischemia. This difference could be due to a vasoactive effect that would improve blood flow in focal ischemia but would not be operative in global ischemia. Therefore, a possible direct cerebrovascular effect of MK-801 was investigated in vitro in basilar arteries from 13 dogs and 16 guinea pigs. Two rings were obtained from each animal; in one the endothelium was removed and in the other the endothelium was maintained intact. Each ring was suspended in an organ bath and isometric tension was recorded. After half-maximal contractions with either KCl or 5-hydroxytryptamine, a dose of MK-801 or the same volume of saline was added to the bath. MK-801 concentrations between 0.1 and 1.0 microM had no effect on both canine and guinea pig basilar arteries with or without endothelium whereas concentrations 10-160 microM further contracted the arteries in an endothelium dependent fashion, with the exception of the KCl precontracted endothelium intact canine artery. Higher concentrations of MK-801 tended to dilate the arteries and the dilation was endothelium independent. Thus, MK-801 has dose-dependent cerebral vascular effects and our results may explain some of the conflicting results of MK-801 on CBF.
Animals↗
Reactivation of arthritis induced by small bowel bacterial overgrowth in rats: role of cytokines, bacteria, and bacterial polymers.
Arthritis is often associated with intestinal diseases, but the etiology is not known. We developed a rat model whereby arthritis was reactivated by experimental small bowel bacterial overgrowth (SBBO). Self-limited monoarticular arthritis was induced by intra-articular injection of 2 micrograms of rhamnose peptidoglycan-polysaccharide derived from group A streptococci into the ankle joints in female Lewis rats. Eleven days after intra-articular injection, when swelling was resolving, experimental SBBO induced by surgical creation of jejunal self-filling blind loops reactivated arthritis, but SBBO induced by creation of self-emptying blind loops, which minimally increases luminal bacteria, and sham operation did not (P < 0.001). Increased joint diameters in rats with self-filling blind loops persisted for at least 56 days after surgery. Reactivation of arthritis due to SBBO was prevented by anti-tumor necrosis factor alpha antiserum and interleukin 1 receptor antagonist (P < 0.001), indicating that these cytokines mediate joint swelling secondary to intestinal injury. Recombinant bactericidal/permeability-increasing protein, an agent which neutralizes endotoxin, and metronidazole, which is active against anaerobic bacteria, prevented arthritis (P < 0.001), but polymyxin B (which also neutralizes endotoxin) and gentamicin had no effect. Mutanolysin, an enzyme which degrades peptidoglycan-polysaccharide from group A streptococci, exacerbated arthritis for the first 6 days but then diminished joint swelling from 12 to 21 days after surgery (P < 0.001). These studies introduce a reproducible animal model of reactivation of arthritis secondary to intestinal injury and demonstrate a role for bacterial products from endogenous enteric organisms.
Animals↗
Mutagenesis of specificity and toxicity regions of a Bacillus thuringiensis protoxin gene.
Two different 30-nucleotide regions of the cryIAc insecticidal protoxin gene from Bacillus thuringiensis were randomly mutagenized. One region was within one of seven amphipathic helices believed to be important for the formation of ion channels. There was no loss of toxicity for three test insects by any of 27 mutants, a result similar to that obtained previously for mutations within another such helix. Only mutations within a region encoding the central helix have resulted in a substantial number of mutants with low or no toxicity. A second mutagenized region encodes amino acids which are unique to this toxin and are within one of the loops in a portion of the toxin important for specificity. Among 21 different mutations of these 10 residues, only changes of two adjacent serine residues resulted in decreased toxicity which was greater for Manduca sexta than for Heliothis virescens larvae. These mutant toxins bound poorly to the single M. sexta CryIAc vesicle-binding protein and to several of the multiple H. virescens-binding proteins. The loop containing these serines must be involved in the formation of a specific toxin recognition domain.
Amino Acid Sequence↗