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E Henderson

Publications and source records attributed to E Henderson.

At least 73 records · Page 4Linked to original sources
PubMed1995

Combining optical and atomic force microscopy for life sciences research.

The atomic force microscope (AFM), a three-dimensional imaging tool that can measure structures from the atomic level to micron scale, has been combined with an inverted optical microscope capable of confocal imaging. The robust design of this microscope, termed the BioScope, enables the operator to use fluorescent markers on a wide variety of biological specimens to determine internal structure to 200 nm resolution and determine surface morphology of the same sample to 20 nm resolution while imaging under physiological conditions. In this report we demonstrate the capabilities of the BioScope by examining living Xenopus retinal glial (XR1) cells, Drosophila polytene chromosomes and colloidal gold-labeled plasmid DNA.

Animals↗
PubMed1994

G-wires: self-assembly of a telomeric oligonucleotide, d(GGGGTTGGGG), into large superstructures.

The telomeric DNA oligonucleotide 5'-G4T2G4-3' (Tet 1.5) spontaneously assembles into large superstructures we have termed G-wires. G-wires can be resolved by gel electrophoresis as a ladder pattern. The self-association of Tet 1.5 is noncovalent and exhibits characteristics of G4-DNA, a parallel four-stranded structure stabilized by guanine tetrads. Formation of G-wires is dependent upon the presence of Na+ and/or K+, and once formed, G-wires are resistant to denaturation. The results described here extend our understanding of the structural potential of G-rich nucleic acids and may provide insight into the possible roles of G-rich sequences and the novel structures they can form in biological systems.

Animals↗
PubMed1994

A protein from Tetrahymena thermophila that specifically binds parallel-stranded G4-DNA.

G4-DNA is a parallel, four-stranded structure mediated by tetrads of hydrogen-bonded guanines (G-quartets). An abundant protein called Tetrahymena G4 binding protein (TGP) that binds to an intermolecular, quadruplex form of d(TTGGGGTTGGGGTTGGGGTTGGGG) under physiological salt conditions has been identified in cellular extracts from the ciliated protozoan Tetrahymena thermophila. In binding competition experiments, molecules capable of forming G4 structures compete for binding to TGP, but non-G4-forming molecules and r(U2G4)4 do not. TGP binding also requires a single-stranded region adjacent to the G4 structure. During the course of this study, it was determined that Mg2+ facilitates the formation of parallel-stranded G4-DNA structures and that high oligonucleotide concentrations are not required to drive formation of these structures. In addition, G4-DNA and TGP/G4-DNA complexes form readily under physiological salt conditions. These data support the proposal that G4-DNA structures exist in vivo.

Animals↗
PubMed1994

Analysis of an insulin gene transcription control element. Positive and negative regulation appears to be mediated by different element sequences.

Pancreatic beta-cell-type-specific transcription of the insulin gene is controlled by cis-acting sequence elements lying within its enhancer region. An essential element required for expression is the insulin control element (ICE). The activity of this element is regulated by both positive- and negative-acting transcription factors. In this study, we have identified the nucleotide sequences within the ICE that are required for repression in noninsulin producing cells. Our results indicate that the cis-acting sequences involved in negative control are distinct from those required in activating expression in beta cells.

Animals↗
PubMed1994

Expression of the trans-active factors that stimulate insulin control element-mediated activity appear to precede insulin gene transcription.

Cell type-specific expression of the major differentiated products of alpha (glucagon) and beta (insulin) cells are regulated by sequences found within their 5'-flanking region. Specific transcription of the insulin gene appears to be principally controlled by a single cis-acting DNA element, termed the insulin control element (ICE). The ICE activator acts in combination with other positive regulatory factors that interact within this region to generate the correct, cell type-specific expression. In the present study, we show that the ICE activator is not only present but is functionally active in the islet glucagon-producing alpha cell line, alpha TC6. Analysis of the expression of various transfected insulin enhancer expression plasmids demonstrated that the insulin enhancer is active in alpha TC6 cells, although at a lower level than in beta cells. The reduced transcription from these constructs appears to be a consequence of the lack of other essential positive regulator(s). The alpha TC6 cells were also shown to display neuronal-like properties. Since islet cells appear to evolve from an alpha-like precursor cell that transiently expresses neuronal cell markers, these results would indicate that the ICE activator factor is induced before transcription of the insulin gene in the developing islet.

Animals↗
PubMed1994

Localization of individual calcium channels at the release face of a presynaptic nerve terminal.

Studies using biophysical techniques suggest a highly structured organization of calcium channels at the presynaptic transmitter release face (Llinás et al., 1981; Stanley, 1993), but it has not as yet proved possible to localize identified channels at the required nanometer level of resolution. We have used atomic force microscopy on the calyx-type nerve terminal of the chick ciliary ganglion to localize single calcium channels tagged via biotinylated omega-conotoxin GVIA to avidin-coated 30 nm gold particles. Calcium channels were in low (modal value approximately < or = 1 per micron 2) and high (modal value approximately 55 per micron 2) density areas and exhibited a prominent interchannel spacing of 40 nm, indicating an intermolecular linkage. Particles were observed in clusters and short linear or parallel linear arrays, groupings that may reflect calcium channel organization at the transmitter release site.

Animals↗
PubMed1994

Human telomeric C-strand tetraplexes.

Telomeric C-strand sequences form non-Watson-Crick base-paired structures in supercoiled plasmids and in oligonucleotides at low pH. Here we examine oligonucleotides composed of 2 or 4 repeats of the human telomeric C-strand sequence d(CCCTAA)n. At low pH, the 2-repeat molecule forms a dimer which exhibits H1'-H1' nuclear Overhauser effects (NOEs) between stacked CC+ base pairs. These NOEs are characteristic of the i-motif, which is a tetraplex composed of two intercalated CC+ duplexes. The 4-repeat molecule forms an intramolecular monomeric structure at low pH, suggesting that four contiguous cytosine tracts fold into a CC+ intercalated tetraplex. These unusual structures may be relevant to the formation of guanine tetraplexes by complementary G-rich sequences. They may also provide a general mechanism for self-recognition by nucleic acids.

Base Sequence↗
PubMed1994

Methicillin-resistant Staphylococcus aureus in tertiary care institutions on the Canadian prairies 1990-1992.

OBJECTIVE: To review experience with methicillin-resistant Staphylococcus aureus (MRSA) in tertiary acute-care teaching hospitals on the Canadian prairies. DESIGN: Retrospective review for a 36-month period, 1990 through 1992. SETTING: Five tertiary acute-care teaching hospitals in three Canadian prairie provinces. METHODS: MRSA isolates and susceptibility were identified through the clinical microbiology laboratory at each institution. For each patient, data collected included duration of institutional residence prior to isolation, patient ethnic background, age, sex, and antimicrobial susceptibility. Epidemiologic typing of strains used restriction fragment length polymorphism analysis by pulsed-field gel electrophoresis. RESULTS: Two hundred fifty-nine MRSA isolates were identified in 135 patients during the 36 months, with substantial institutional variation in number of isolates. No consistent increase in yearly numbers of isolates was apparent. Patients usually had MRSA identified at admission (62%); only one of five centers had the majority of isolates acquired nosocomially. Patients with MRSA present at admission were more frequently of aboriginal (First Nations) ethnicity (62% compared with 14% of nosocomial; P < 0.001). Pulsed-field gel electrophoresis of 167 isolates from 135 patients revealed 46 different strains with little interprovincial or interinstitutional identity of strains. CONCLUSIONS: MRSA isolated in patients in tertiary care institutions in these three Canadian provinces usually is acquired prior to admission. A disproportionate number of isolates are identified in aboriginal Canadians. Epidemiologic typing was consistent with a polyclonal origin of MRSA in this geographic area.

Adult↗
PubMed1994

Cardiorespiratory and symptomatic variables during maximal and submaximal exercise in men with stable effort angina: a comparison of atenolol and celiprolol.

Celiprolol is a novel beta 1 selective adrenoreceptor blocker with partial beta 2 agonism and direct vasodilator activity. These ancillary properties may reduce symptomatic breathlessness and fatigue and modify respiration during exercise. To test this hypothesis 20 men with stable effort angina were enrolled in a double-blind crossover study to investigate the effects of atenolol 100 mg once daily (A) and celiprolol 400 mg once daily (C) on cardiorespiratory and symptomatic variables during maximal and submaximal exercise. Total exercise time on a modified Bruce protocol was similar on both treatments: C12.5 min, A 13.1 min. During steady state submaximal exercise at 60-75% (mean 68%) of maximum work capacity, minute ventilation (C33.81 min-1, A 33.51 min-1), oxygen uptake (C14.6 ml.kg-1.min-1, A15.1 ml.kg-1.min-1), respiratory exchange ratio (C 0.89, A 0.87), ratio of VE/VCO2 (C 33.6, A 33.4), ratio of VE/VO2 (C 2.34, A 2.72), Borg perceived exertion score (C 11.2, A 10.9) and visual analogue scores for breathlessness (C 29.5, A 25.9) and muscle fatigue (C 28.9, A 26.0) were all similar on both treatments. At maximal exercise capacity on the modified Bruce protocol, minute ventilation (C 58.31 min-1, A 60.41 min-1), oxygen uptake (C 21.3 ml.kg-1.min-1, A 21.7 ml.kg-1.min-1), respiratory exchange ratio (C 1.02, A.1.05), ratio VE/VCO2 (C 34.8, A 35.9), and ratio VE/VO2 (C 2.80, A 2.83) were also similar on both drugs. Over a 10 day period anginal attacks (C 10.1 +/- 10.4, A 5.4 +/- 5.9) and sublingual GTN use (C 5.9 +/- 10.3, A 4.4 +/- 9.8) were both more frequent on celiprolol).(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1994

c-jun inhibits transcriptional activation by the insulin enhancer, and the insulin control element is the target of control.

Selective transcription of the insulin gene in pancreatic beta cells is regulated by its enhancer, located between nucleotides -340 and -91 relative to the transcription start site. One of the principal control elements within the enhancer is found between nucleotides -100 and -91 (GCCATCTGCT, referred to as the insulin control element [ICE]) and is regulated by both positive- and negative-acting transcription factors in the helix-loop-helix (HLH) family. It was previously shown that the c-jun proto-oncogene can repress insulin gene transcription. We have found that c-jun inhibits ICE-stimulated transcription. Inhibition of ICE-directed transcription is mediated by sequences within the carboxy-terminal region of the protein. These c-jun sequences span an activation domain and the basic leucine zipper DNA binding-dimerization region of the protein. Both regions of c-jun are conserved within the other members of the jun family: junB and junD. These proteins also suppress ICE-mediated transcription. The jun proteins do not appear to inhibit insulin gene transcription by binding directly to the ICE. c-jun and junB also block the trans-activation potential of two skeletal muscle-specific HLH proteins, MyoD and myogenin. These results suggests that the jun proteins may be common transcription control factors used in skeletal muscle and pancreatic beta cells to regulate HLH-mediated activity. We discuss the possible significance of these observations to insulin gene transcription in pancreatic beta cells.

Animals↗
PubMed1994

Isolation and characterization of a novel transcription factor that binds to and activates insulin control element-mediated expression.

Pancreatic beta-cell-type-specific transcription of the insulin gene is principally regulated by a single cis-acting DNA sequence element, termed the insulin control element (ICE), which is found within the 5'-flanking region of the gene. The ICE activator is a heteromeric complex composed of an islet alpha/beta-cell-specific factor associated with the ubiquitously distributed E2A-encoded proteins (E12, E47, and E2-5). We describe the isolation and characterization of a cDNA for a protein present in alpha and beta cells, termed INSAF for insulin activator factor, which binds to and activates ICE-mediated expression. INSAF was isolated from a human insulinoma cDNA library. Transfection experiments demonstrated that INSAF activates ICE expression in insulin-expressing cells but not in non-insulin-expressing cells. Cotransfection experiments showed that activation by INSAF was inhibited by Id, a negative regulator of basic helix-loop-helix (bHLH) protein function. INSAF was also shown to associate in vitro with the bHLH protein E12. In addition, affinity-purified INSAF antiserum abolished the formation of the activator-specific ICE-binding complex. Immunohistochemical studies indicate that INSAF is restricted in terms of its expression pattern, in that INSAF appears to be detected only within the nuclei of islet pancreatic alpha and beta cells. All of these data are consistent with the proposal that INSAF is either part of the ICE activator or is antigenically related to the specific activator required for insulin gene transcription.

Amino Acid Sequence↗
PubMed1994

XIHbox 8, an endoderm-specific Xenopus homeodomain protein, is closely related to a mammalian insulin gene transcription factor.

The cis-acting sequences that mediate insulin gene expression exclusively in pancreatic islet beta-cells are localized within the 5'-flanking region between nucleotides -340 and -91. We have identified an evolutionarily conserved, A+T-rich element at -201/-196 basepairs in the rat insulin II gene that is essential for efficient expression in beta-cells. Affinity-purified antibody to the XIHbox 8 protein super-shifted the major beta-cell-activator factor complex binding to the -201/-196 element. XIHbox 8 is a Xenopus endoderm-specific homeodomain protein whose expression is restricted to the nucleus of endodermal cells of the duodenum and developing pancreas. Antibody to XIHbox 8 specifically interacts with a 47-kilodalton protein present in this DNA complex. Immunohistochemical studies revealed XIHbox 8-like proteins within the nucleus of almost all mouse islet beta-cells and a subset of islet alpha- and beta-cells. These results are consistent with the proposal that an XIHbox 8-related homeoprotein of 47 kilodalton is required for expression of the mammalian insulin gene in beta-cells. Experiments conducted with antiserum raised to somatostatin transcription factor-1 (STF-1), a recently isolated mammalian XIHbox 8-related homeoprotein, indicate that the STF-1 protein is the mammalian homolog of Xenopus XIHbox 8.

Amino Acid Sequence↗
PubMed1993

Properties of an xeroderma pigmentosum revertant cell line expressing endonuclease V.

We have developed a set of cell lines to help distinguish the sequelae of specific lesions in DNA after UV irradiation. Irradiation results in two primary lesions: cyclobutane dimers and pyrimidine-pyrimidone (6-4) photoproducts. The contributions of each to mutation are considered utilizing a spectrum of cell lines with increasing abilities to repair these lesions. In particular, we focus on a revertant of the XP12Ro(M1) cell line from a patient with Xeroderma pigmentosum, XP129, which is capable of repairing (6-4) photoproducts but not cyclobutane dimers. We have successfully introduced the denV gene into these cells which confers the ability to repair cyclobutane dimers. By comparing the results of a shuttle vector mutation experiment with the vector pZ189, we can correlate specific mutations to specific lesions.

Base Sequence↗
PubMed1993

Atomic force microscopy of oriented linear DNA molecules labeled with 5nm gold spheres.

The atomic force microscope (AFM;1) can image DNA and RNA in air and under solutions at resolution comparable to that obtained by electron microscopy (EM) (2-7). We have developed a method for depositing and imaging linear DNA molecules to which 5nm gold spheres have been attached. The gold spheres facilitate orientation of the DNA molecules on the mica surface to which they are absorbed and are potentially useful as internal height standards and as high resolution gene or sequence specific tags. We show that by modulating their adhesion to the mica surface, the gold spheres can be moved with some degree of control with the scanning tip.

DNA↗
PubMed1993

Imaging F-actin in fixed glial cells with a combined optical fluorescence/atomic force microscope.

A prototype combined optical fluorescence/atomic force microscope (OFAFM) designed for use in neurobiology and related disciplines has been constructed and used to study filamentous actin (F-actin) and other cellular structures in fixed Xenopus retinal glial cells (XR1 glial cell line). F-actin was readily observed by both fluorescence and AFM. AFM images of nuclei and other cellular structures were also obtained. The OFAFM consists of an AFM with an interferometer detection mechanism mounted on an inverted optical microscope. Integration of optical and scanned probe imaging methods provides a unique and useful approach to studying glial (and other) cell structure and function.

Actins↗
PubMed1993

Acute effects of cicletanine in angina pectoris.

The anti-anginal properties of single doses of a new anti-hypertensive drug, cicletanine, were investigated in a double-blind, randomised, balanced, crossover comparison with placebo in sixteen patients with chronic stable angina pectoris. All subjects underwent treadmill exercise 2 h after drug administration and 24 h ambulatory ECG monitoring with ST scanning. Although there were significantly fewer episodes of ST depression on ambulatory monitoring after cicletanine, total exercise duration and time to 1 mm ST depression were unchanged. This report provides little evidence of an acute anti-anginal effect of cicletanine but longer term studies may be indicated to further evaluate this drug's potential role in the management of angina pectoris.

Adult↗
PubMed1993

Colloidal gold particles as an incompressible atomic force microscope imaging standard for assessing the compressibility of biomolecules.

Colloidal gold particles have multiple uses as three-dimensional atomic force microscopy imaging standards because they are incompressible, monodisperse, and spherical. The spherical nature of the particles can be exploited to characterize scanning tip geometry. As uniform spheres, colloidal gold particles may be used to calibrate the vertical dimensions of atomic force microscopy at the nanometer level. The monodisperse and incompressible nature of the gold can be used to characterize the vertical dimensions of coadsorbed biomolecules. Simultaneous measurements of gold with tobacco mosaic virus show that, at the same applied vertical force, the tobacco mosaic virus is undamaged by blunt tips but is compressed or disintegrated under sharper scanning styli, suggesting that specimen degradation is partly a pressure-dependent effect.

Biophysical Phenomena↗