Search PubMed⌕ Search

Biomedical subjects

R Hull

Publications and source records attributed to R Hull.

At least 19 recordsLinked to original sources
PubMed2000

New mechanism for dislocation blocking in strained layer epitaxial growth

Dislocation interactions play a critical role in plasticity and heteroepitaxial strain relaxation. We use real time transmission electron microscopy observations of the interaction between threading and misfit dislocations in SiGe heterostructures to investigate interactions quantitatively. In addition to the expected long-range blocking of threading segments, we observe a new short-range mechanism which is significantly more effective. Simulations show that this reactive blocking occurs when two dislocations with the same Burgers vector reconnect.

Journal Article↗
PubMed2000

Sublethal lead affects pituitary function of rainbow trout during exogenous vitellogenesis.

Sexually maturing female rainbow trout, Oncorhynchus mykiss, were exposed to 10 microg/L of waterborne lead Pb(NO(3))(2) for 12 days during endogenous vitellogenesis and 12 days during exogenous vitellogenesis. Lead had no significant effect on either gonadosomatic indices or mean maximum diameters of developing oocytes during early vitellogenesis. When females were exposed during exogenous vitellogenesis, however, both GSI and oocyte growth were significantly different from controls on day 12. Similarly GSI and oocyte growth was significantly reduced in lead-exposed fish. Atomic absorption spectroscopy measurements of lead levels in liver, ovaries, and blood tissues showed significant levels of lead in the blood. Lead did not accumulate in either the ovaries or the liver. Analysis of pituitary basophils during both endogenous and exogenous vitellogenesis and subsequent comparison with reproductive parameters in the ovaries indicated that GtH-basophils did not significantly increase in controls during endogenous vitellogenesis, and there was no significant change in GSI or ovarian growth in either controls or lead-exposed females. However during exogenous vitellogenesis, control basophils significantly increased over the 12-day experiment, but were not significantly different over 12 days in lead-exposed females. Both GSI and oocyte growth were significantly different from controls in lead-exposed females. The results suggest that naturally occurring changes in GTH-producing basophils during vitellogenesis alters GSI and oocyte growth in female rainbow trout exposed to lead during exogenous vitellogenesis, but not during endogenous vitellogenesis.

Animals↗
PubMed2000

Interaction of yellow fever virus French neurotropic vaccine strain with monkey brain: characterization of monkey brain membrane receptor escape variants.

Binding of yellow fever virus wild-type strains Asibi and French viscerotropic virus and vaccine strains 17D and FNV to monkey brain and monkey liver cell membrane receptor preparations (MRPs) was investigated. Only FNV bound to monkey brain MRPs, while French viscerotropic virus, Asibi, and FNV all bound to monkey liver MRPs. Four monkey brain and two mouse brain MRP escape (MRP(R)) variants of FNV were selected at pH 7.6 and 6.0. Three monkey brain MRP(R) variants selected at pH 7.6 each had only one amino acid substitution in the envelope (E) protein in domain II (E-237, E-260, or E274) and were significantly attenuated in mice following intracerebral inoculation. Two of the variants were tested in monkeys and retained parental neurotropism following intracerebral inoculation at the dose tested. We speculate that this region of domain II is involved in binding of FNV E protein to monkey brain and is, in part, responsible for the enhanced neurotropism of FNV for monkeys. A monkey brain MRP(R) variant selected at pH 6.0 and two mouse brain MRP(R) variants selected at pH 7.6 were less attenuated in mice, and each had an amino acid substitution in the transmembrane region of the E protein (E-457 or E-458).

Animals↗
PubMed2000

Evolution of the Sabin strain of type 3 poliovirus in an immunodeficient patient during the entire 637-day period of virus excretion.

A 20-year-old female hypogammaglobulinemic patient received monotypic Sabin 3 vaccine in 1962. The patient excreted type 3 poliovirus for a period of 637 days without developing any symptoms of poliomyelitis, after which excretion appeared to have ceased spontaneously. The evolution of Sabin 3 throughout the entire period of virus excretion was studied by characterization of seven sequential isolates from the patient. The isolates were analyzed in terms of their antigenic properties, virulence, sensitivity for growth at high temperatures, and differences in nucleotide sequence from the Sabin type 3 vaccine. The isolates followed a main lineage of evolution with a rate of nucleotide substitution that was very similar to that estimated for wild-type poliovirus during person-to-person transmission. There was a delay in the appearance of antigenic variants compared to sequential type 3 isolates from healthy vaccines, which could be one of the possible explanations for the long-term excretion of virus from the patient. The distribution of mutations in the isolates identified regions of the virus possibly involved in adaptation for growth in the human gut and virus persistence. None of the isolates showed a full reversion of the attenuated and temperature-sensitive phenotypes of Sabin 3. Information of this sort will help in the assessment of the risk of spread of virulent polioviruses from long-term excretors and in the design of therapies to stop long-term excretion. This will make an important contribution to the decision-making process on when to stop vaccination once wild poliovirus has been eradicated.

3C Viral Proteases↗
PubMed2000

Urinary tract infection prophylaxis using Escherichia coli 83972 in spinal cord injured patients.

PURPOSE: Escherichia coli 83972 was previously shown to establish bladder colonization in select patient groups. We evaluate the safety and feasibility of using bacterial interference with E. coli 83972 to prevent urinary tract infection in spinal cord injured patients. MATERIALS AND METHODS: A total of 21 men and women with neurogenic bladder secondary to spinal cord injury underwent intravesical inoculation with E. coli 83972. Frequency of symptomatic urinary tract infection before and after colonization was compared. RESULTS: Successful long-term bladder colonization was achieved in 13 study participants. Mean duration of colonization was 12.3 months (range 2 to 40). Subjects had no symptoms of urinary tract infection while colonized with E. coli 83972 (0 infection per 18.4 patient-years). Successfully colonized subjects had experienced a mean of 3.1 symptomatic urinary tract infections per year (range 2 to 7) before colonization. Symptomatic infection also occurred in 4 subjects who were not successfully colonized with E. coli 83972 and in 7 others after spontaneous loss of colonization. Colonized subjects reported subjective improvement in quality of life with respect to urinary tract infection while colonized. CONCLUSIONS: E. coli 83972 may be safely used to establish long-term asymptomatic bladder colonization in spinal cord injured subjects. Preliminary findings suggest that colonization with E. coli 83972 may reduce the frequency of urinary tract infection in patients with neurogenic bladder secondary to spinal cord injury.

Adult↗
PubMed1999

Integration of banana streak badnavirus into the Musa genome: molecular and cytogenetic evidence.

Breeding and tissue culture of certain cultivars of bananas (Musa) have led to high levels of banana streak badnavirus (BSV) infection in progeny from symptomless parents. BSV DNA hybridized to genomic DNA of one such parent, Obino l'Ewai, suggesting integration of viral sequences. Sequencing of clones of Obino l'Ewai genomic DNA revealed an interface between BSV and Musa sequences and a complex BSV integrant. In situ hybridization revealed two different BSV sequence locations in Obino l'Ewai chromosomes and a complex arrangement of BSV and Musa sequences was shown by probing stretched DNA fibers. This is the first report of integrated sequences that possibly lead to a plant pararetrovirus episomal infection by a mechanism differing markedly from animal retroviral systems.

Badnavirus↗
PubMed1999

Evidence that badnavirus infection in Musa can originate from integrated pararetroviral sequences.

When some virus- and disease-free Musa spp. (banana and plantain) are propagated by tissue culture, the resulting plants develop infections with banana streak badnavirus (BSV), a pararetrovirus. In sharp contrast to the virion DNA recovered from natural infections, the virion DNA from tissue culture-associated infections of different Musa spp. was highly similar if not identical. Although BSV does not employ integration during the infection cycle, BSV DNA was found to be integrated into the Musa genome. While one integration consisted of a partial BSV genome, a second contained more than one complete genome that was almost identical to BSV recovered from tissue culture-derived plants. The arrangement of this integrated BSV DNA suggests that it can yield an infectious episomal genome via homologous recombination. This report documents the first instance of integrated DNA of a nonintegrating virus giving rise to an episomal viral infection and identifies tissue culture as a possible trigger for the infection, raising the question of whether similar activatable viral sequences exist in the genomes of other plants and animals.

Badnavirus↗
PubMed1999

Detection of episomal banana streak badnavirus by IC-PCR.

A polymerase chain reaction (PCR) based strategy to detect episomal banana streak badnavirus (BSV) in banana and plantain plants that carry integrated BSV sequences was developed. Antisera used in immuno-capture polymerase chain reaction (IC-PCR) are capable of binding a large number of BSV serotypes. The primers used for PCR are capable of annealing to and amplifying across the aspartic protease-reverse transcriptase domain boundaries of both episomal and integrated BSV sequences and result in similar or identical sequence size fragments from either template. However, we show that under the conditions selected for IC-PCR, nuclear, mitochondrial or chloroplast genomic sequences are not amplified and thus only captured episomal BSV is amplified. IC-PCR is suitable for the large-scale screening of Musa for episomal BSV which is necessary for germplasm movement.

Badnavirus↗
PubMed1999

Original reverse transcription polymerase chain reaction method to obtain the full-length cDNA of rice tungro spherical virus.

A two-step reverse transcription reaction combined with long PCR was developed in order to obtain the full-length cDNA from the 12.2 kbp genomic RNA of rice tungro spherical virus. A first step reverse transcription, performed at 45 degrees C using a reverse transcriptase deprived of RNase H activity, allowed the synthesis of a nearly full-length cDNA of 11.7 kbp. A second step reaction, carried out at 65 degrees C using a thermostable polymerase, was necessary to destabilise secondary structures present at the 5' extremity of the RNA template which hampered the reverse transcription reaction in this region. The full-length cDNA obtained by the two-step reverse transcription was amplified successfully by long PCR and subsequently cloned into a plasmid vector. The cloned cDNA showed toxicity and proved to be unstable when amplified in E. coli.

Cloning, Molecular↗
PubMed1999

Analysis of the sequence of dioscorea Alata bacilliform virus: comparison to others members of the badnavirus group.

The complete nucleotide sequence of the genome of Dioscorea alata bacilliform virus (DaBV) has been determined from cloned fragments. Features of the genome confirm DaBV to be a pararetrovirus of the genus Badnavirus which is more similar to other mealy-bug transmitted badnaviruses, in particular to cacao swollen shoot virus, than to rice tungro bacilliform virus. Sequence variability between cloned fragments suggests that the genetic variability of the virus may be quite high (up to 11% nucleotide sequence variation for some small regions of the genome) although the overall variability detected was 4.2% at the nucleotide level.

Badnavirus↗
PubMed1999

[Western blotting of RStV gene products in rice and insects].

The NS3 and NC protein genes encoded by RNA3 of RStV, the NCP and NSvc4 protein genes encoded by RNA4 were subcloned into the E. coli expression vector pGEX3X to express four groups of fusion protein under IPTG induction. These fusion proteins were used to immunize rabbits to raise antisera. The antisera against the E. coli-expressed proteins were available for probing the presence of the viral gene products in both rice plant and insect hosts. The expected gene products can be probed only in diseased rice plant with NCP antiserum and the corresponding products detected in both plant and RStV particle preparation with NC antiserum. The viral gene products probed by NS3 and NSvc4 antisera were different from the expected ones in size.

Animals↗
PubMed1998

Mechanisms of protection induced by attenuated simian immunodeficiency virus. II. Lymphocyte depletion does not abrogate protection.

To determine the role that cellular immune responses play in the protection conferred by vaccination with attenuated SIVmac32H (pC8), we have attempted to deplete macaques of their CD8+ cells prior to challenge with wild-type SIVmac32H (pJ5). In two of four pC8-infected macaques, N109 and N112, a transient partial depletion of CD8+ cells by antibody treatment was achieved. On the day of challenge peripheral CD2+CD4-CD8+ cell counts were reduced by 92 and 95%, respectively, in animals N109 and N112 and their lymph nodes revealed a 46 and 58% reduction, respectively, in CD2+CD4-CD8+ cells. Two other pC8-immunized macaques, N110 and N111, treated in the same way, did not show significant depletion of CD8+ cells. None of these four pC8-immunized animals became infected when challenged with 50 MID50 of pJ5. Treatment of a further four pC8-infected and protected macaques and two naive control animals with Campath-1H antibody successfully depleted peripheral CD3+ cell counts by >99% in all treated animals. Campath-1H depletion resulted in enhanced, longer lasting lymphoid depletion. Yet subsequent challenge with 20 MID50 of pJ5 still failed to infect the pC8-immunized animals. All eight of the naive controls, including two Campath-1H-treated animals, became infected following challenge. In summary, partial depletion of circulating CD8+ cells or total lymphocytes prior to challenge failed to abrogate the protection conferred by vaccination with pC8.

Animals↗
PubMed1998

Rice tungro spherical virus polyprotein processing: identification of a virus-encoded protease and mutational analysis of putative cleavage sites.

Rice tungro spherical virus encodes a large polyprotein containing motifs with sequence similarity to viral serine-like proteases and RNA polymerases. Polyclonal antisera raised against domains of the putative protease and polymerase in fusion with glutathione S-transferase detected a protein of about 35 kDa and, in very low amounts, a protein of about 70 kDa, respectively, in extracts from infected plants. In in vitro transcription/translation systems and in Escherichia coli we demonstrated a proteolytic activity in the C-terminal region of the polyprotein. This protease rapidly cleaved its polyprotein precursors in vitro. Mutating a potential cleavage site located N-terminal to the protease domain, Gln2526-Asp2527, diminished processing. The transversion mutation at the putative C-terminal cleavage site of the protease, at Gln2852-Ala2853, led to a delayed and partial processing.

Base Sequence↗
PubMed1998

In Situ Studies of the Interaction of Dislocations with Point Defects during Annealing of Ion Implanted Si/SiGe/Si (001) Heterostructures.

: Strained layer heterostructures provide ideal systems with which to study the dynamics of dislocation motion via in situ transmission electron microscopy, as the geometry, strain state, and kinetics can be characterized and directly controlled. We discuss how these structures are used to study dislocation-point defect interactions, emphasizing the experimental requirements necessary for quantification of dislocation motion. Following ion implantation, different concentrations and types of point defects are introduced within the SiGe epilayer depending on the implantation species, energy, and current density. By annealing samples in situ in the transmission electron microscope (TEM) following implantation, we can directly observe dislocation motion and quantify the effect of dislocation-point defect interactions on dislocation velocities. We find that dislocation motion is impeded if the implantation dose peak lies within the epilayer, as dislocations pin at point defect atmospheres. Shallow BF2 implantation into the sample capping layer results in more complicated behavior. For low current density implants, dislocation velocities may be dramatically increased; at higher current densities the magnitude of this increase is significantly smaller. Implantation of different ions separately implicates fluorine as the species responsible for the observed increases in dislocation velocities, presumably due to an electrical effect on the rate of dislocation kink nucleation.

Journal Article↗
PubMed1998

Applications of Ion Microscopy and In Situ Electron Microscopy to the Study of Electronic Materials and Devices.

: We discuss the application of ion microscopy and in situ electron microscopy to the study of electronic and optical materials and devices. We demonstrate how the combination of in situ transmission electron microscopy and focused ion beam microscopy provides new avenues for the study for such structures, enabling extension of these techniques to the study of dopant distributions, nanoscale stresses, three-dimensional structural and chemical reconstruction, and real-time evolution of defect microstructure. We also discuss in situ applications of thermal, mechanical, electrical, and optical stresses during transmission electron microscopy imaging.

Journal Article↗
PubMed1998

Cloning and sequence analysis of banana streak virus DNA.

Banana streak virus (BSV), a member of the Badnavirus group of plant viruses, causes severe problems in banana cultivation, reducing fruit yield and restricting plant breeding and the movement of germplasm. Current detection methods are relatively insensitive. In order to develop a PCR-based diagnostic method that is both reliable and sensitive, the genome of a Nigerian isolate of BSV has been sequenced and shown to comprise 7389 bp and to be organized in a manner characteristic of badnaviruses. Comparison of this sequence with those of other badnaviruses showed that BSV is a distinct virus. PCR with primers based on sequence data indicated that BSV sequences are present in the banana genome.

Amino Acid Sequence↗