Biomedical subjects

B Visser

Publications and source records attributed to B Visser.

At least 19 recordsLinked to original sources

PubMed2005

A new population of very high energy gamma-ray sources in the Milky Way.

Very high energy gamma-rays probe the long-standing mystery of the origin of cosmic rays. Produced in the interactions of accelerated particles in astrophysical objects, they can be used to image cosmic particle accelerators. A first sensitive survey of the inner part of the Milky Way with the High Energy Stereoscopic System (HESS) reveals a population of eight previously unknown firmly detected sources of very high energy gamma-rays. At least two have no known radio or x-ray counterpart and may be representative of a new class of "dark" nucleonic cosmic ray sources.

Journal Article↗

PubMed2004

High-energy particle acceleration in the shell of a supernova remnant.

A significant fraction of the energy density of the interstellar medium is in the form of high-energy charged particles (cosmic rays). The origin of these particles remains uncertain. Although it is generally accepted that the only sources capable of supplying the energy required to accelerate the bulk of Galactic cosmic rays are supernova explosions, and even though the mechanism of particle acceleration in expanding supernova remnant (SNR) shocks is thought to be well understood theoretically, unequivocal evidence for the production of high-energy particles in supernova shells has proven remarkably hard to find. Here we report on observations of the SNR RX J1713.7 - 3946 (G347.3 - 0.5), which was discovered by ROSAT in the X-ray spectrum and later claimed as a source of high-energy gamma-rays of TeV energies (1 TeV = 10(12) eV). We present a TeV gamma-ray image of the SNR: the spatially resolved remnant has a shell morphology similar to that seen in X-rays, which demonstrates that very-high-energy particles are accelerated there. The energy spectrum indicates efficient acceleration of charged particles to energies beyond 100 TeV, consistent with current ideas of particle acceleration in young SNR shocks.

Journal Article↗

PubMed2000

The effect of arm and wrist supports on the load of the upper extremity during VDU work.

OBJECTIVE: To evaluate the effectiveness of arm and wrist supports in reducing the workload during computer work. DESIGN: Female subjects (n=10) performed computer work in conditions with arm or wrist supports and in a condition without supports. BACKGROUND: Sustained muscle tension in the trapezius muscle is a risk factor for trapezius myalgia. Arm and wrist supports are used at the workplace with the intention to reduce the muscle tension. The effectiveness of these aids in reducing the load is not clear. METHODS: A typing task and mouse task were performed, each with four types of supports and without support. Electromyography and subjective ratings were used to quantify the workload. RESULTS: Lower levels of trapezius muscle activation were recorded with the use of arm supports. Wrist supports did not reduce activation. The rated perceived workload did not discriminate. CONCLUSIONS: Reduction of muscle activation in the neck-shoulder region during standard visual display unit work can be achieved with arm supports. Wrist supports do not reduce the strain on the neck-shoulder region. Subjective ratings seem not of use in selecting ergonomic aids in low intensity tasks. RelevanceVisual display unit workers are at risk of developing complaints of the neck and upper extremity. Arm and wrist supports are introduced at the workplace to reduce the workload. If arm and wrist supports are effective in reducing the workload they might be of use as preventive measures to reduce the risk of neck-shoulder complaints.

Adult↗

PubMed2000

Predicting mechanical load of the glenohumeral joint, using net joint moments.

OBJECTIVE: To evaluate the relationship between net moments for the glenohumeral joint as calculated with a model that is easy to apply (Static Strength Prediction Program (SSPP)) and the internal forces, calculated with a simulation model of the human shoulder (Delft Shoulder Model, DSM). DESIGN: Static recordings of bony landmarks of the shoulder girdle during prescribed arm motions using a three-dimensional (3D) digitizer. BACKGROUND: The SSPP is a biomechanical model for the evaluation of workload. Concerning the shoulder the output of the model consists of net moments in the glenohumeral joint. For the glenohumeral joint the relationship between net joint moments and internal load predictions is unknown, therefore it is useful to investigate whether the SSPP can be used to predict mechanical load in the glenohumeral joint. METHODS: 3D co-ordinates of bony landmarks of the shoulder girdle are recorded, in variable arm positions, in four different planes. RESULTS: A strong linear relationship between compression forces and net moments is found, which makes it reasonable to assume a direct relationship between net moments and joint compression forces. CONCLUSIONS: (a) Net joint moments appeared to be a good indicator for mechanical load in the glenohumeral joint in static situations. (b) The SSPP can be used to predict these joint moments for static situations. RELEVANCE: biomechanical models predicting mechanical load can be used in work situations in order to prevent overload and injuries, as well as in many other areas, for instance to evaluate the mechanical load during wheelchair propulsion.

Adult↗

PubMed1999

Estimating net lumbar sagittal plane moments from EMG data. The validity of calibration procedures.

In the present study the validity of EMG based methods to estimate the net moment working at the lumbar spine was investigated. Eight subjects performed a series of static and dynamic tasks. EMG was recorded from 8 locations over the back muscles. At the same time force platform and kinematic data for a linked segment analysis were collected. The net moment at the lumbar spine was calculated from the latter data and compared to EMG based estimates of the same moment. These estimates were derived from a linear regression between the EMG amplitudes and the net moments obtained during static ramp calibrations. It appeared that calibration in several postures, covering the range occurring in the tasks studied, and in a posture in the middle of this range, yielded estimates of the group averaged 10th, 50th, and 90th percentile of the net moments which were within 10% of the real value. The explained variance obtained in the calibration procedure proved not to be a good indicator of the validity of the procedure.

Adult↗

PubMed1999

Characterization of an Arabidopsis thaliana receptor-like protein kinase gene activated by oxidative stress and pathogen attack.

An Arabidopsis thaliana cDNA clone that encodes a putative receptor-like protein kinase gene (At-RLK3) was characterized. The deduced 667-amino acid protein consists of an amino-terminal signal sequence, an extracellular domain, a single transmembrane domain, and a cytoplasmic domain with characteristics of serine/threonine protein kinase. Because of the original features of its extracellular domain, the At-RLK3 protein is a member of a new class of receptor-like protein kinases. The At-RLK3 gene is present as a single copy within the Arabidopsis genome and its transcripts are detected in root, stem, leaf and flower. In cultured cells, the At-RLK3 gene is activated upon oxidative stress and salicylic acid treatment. In plants, the gene appears to be differentially regulated during various plant-pathogen interactions: upon inoculation with strains of Pseudomonas syringae pv. tomato harboring or not, different avr genes, At-RLK3 transcripts accumulate transiently at similar levels during both compatible and incompatible interactions. This gene is, however, preferentially expressed during the incompatible interaction induced by the soil-borne vascular bacteria, Ralstonia solanacearum. The involvement of At-RLK3 in signal transduction pathways during pathogen attack is discussed.

Amino Acid Sequence↗

PubMed1999

Job rotation as a factor in reducing physical workload at a refuse collecting department.

The effect of job rotation on the physical workload was investigated for male employees working at a refuse collecting department. Before the introduction of job rotation, an employee worked as a street sweeper, as a refuse collector or as a driver. After the introduction of job rotation, every employee was allowed to alternate between two of the three possible jobs during the day, i.e. refuse collecting/street sweeping, refuse collecting/driving or street sweeping/driving. Two non-rotation groups (i.e. refuse collectors and street sweepers) and two rotation groups (i.e. refuse collectors/street sweepers and street sweepers/drivers) were mutually compared. The physical workload was determined by measuring the perceived load, energetic load and postural load during a full working day. Job rotation resulted in a significant decrease of the perceived load and energetic load and a slight decrease of the postural load. The results indicate that the total amount of work performed by means of job rotation resulted in an overall reduced physical workload of the employees of the refuse collecting department.

Adult↗

PubMed1997

High-dose regimen of interleukin-2 and interferon-alpha in combination with lymphokine-activated killer cells in patients with metastatic renal cell cancer.

Seventy-two patients with metastatic renal cell cancer were treated with the combination of high-dose interleukin-2 (IL2), interferon-alpha (IFN alpha), and lymphokine-activated killer cells (LAK). Seventeen patients were entered in a feasibility part of the study (protocol 1) and 55 in an efficacy part (protocol 2). Protocol 2 differed from protocol 1 in the addition of IFN alpha to the first 5 days of IL2 infusion. Each patient was planned to receive two induction cycles. IL2, 18 MIU/m2/day, was administered continuously i.v. on days 1-5, and IFN alpha, 5 MIU/m2/day (protocol 2), was administered i.m. on days 1-5, followed by three daily lymphaphereses on days 7-9. On day 12, treatment was resumed with IL2 and IFN alpha on days 12-15 and LAK reinfusions on days 12-14. In protocol 1, three complete (CR) and one partial (PR) responses were achieved (response rate 24%). The median duration of response and the median survival were 18.1 and 13.9 months, respectively. The 3-year survival was 35%. Of the 51 evaluable patients in protocol 2, 6 achieved a CR and 13 a PR (response rate 37%). The median duration of response was 11.1 months. The median survival was 16.9 months. The 3-year survival was 35%. There were three treatment-related deaths. Other severe toxicities included hypotension, cardiotoxicity, pulmonary edema, renal toxicity, and infectious complications. In the two induction cycles, only 54 and 42% of the planned doses could be administered. We conclude that the use of high-dose regimens of IL2 and IFN alpha is not warranted, unless we can define more accurately which patients may experience long-term survival as a result of treatment.

Adoptive Transfer↗

PubMed1996

Weight and frequency effect on spinal loading in a bricklaying task.

In manual materials handling jobs a reduction in the weight of materials often concurs with an increase in handling frequency. The effect of weight and inversely related frequency on spinal load was studied in two bricklaying tasks: building the skin and the floor of a steel ladle. In both tasks five subjects laid bricks of varying weight and frequency (obtained from field observations). The load parameters investigated were peak values and time integrals of the compressive force on the L5-S1 motion segment and stature loss, which is assumed to reflect motion segment creep due to compression. Peak compression was found to increase at higher brick weights. No differences in integrated compression were observed among four out of five combinations of weight and frequency (both in skin and floor building). Laying bricks for a fixed period of 47 min yielded average stature losses of 2.0 3.6 mm. Differences in stature loss among weight-frequency conditions were not significant. In conclusion, at lower weights peak loads decrease, but the benefit of this should be doubted because the frequency of exposure to these peak loads was found to increase. Moreover, this increase was such that no effects were found on spinal load estimates that incorporate both magnitude and time aspects of the load, like time-integrated compression and stature loss.

Adult↗

PubMed1995

Mapping and characterization of the entomocidal domain of the Bacillus thuringiensis CryIA(b) protoxin.

The amino acid sequences necessary for entomocidal activity of the CryIA(b) protoxin of Bacillus thuringiensis were determined. Introduction of stop codons behind codons Arg601, Phe604 or Ala607 showed that amino acid residues C-terminal to Ala607 are not required for insecticidal activity and that activation by midgut proteases takes place distal to Ala607. The two shortest polypeptides, deleted for part of the highly conserved beta-strand, were prone to proteolytic degradation, explaining their lack of toxicity. Apparently, this beta-strand is essential for folding of the molecule into a stable conformation. Proteolytic activation at the N-terminus was investigated by removing the first 28 codons, resulting in a translation product extending from amino acid 29 to 607. This protein appeared to be toxic not only to susceptible insect larvae such as Manduca sexta and Heliothis virescens, but also to Escherichia coli cells. An additional mutant, encoding only amino acid residues 29-429, encompassing the complete putative pore forming domain, but lacking a large part of the receptor-binding domain, was similarly toxic to E. coli cells. This suggests a role for the N-terminal 28 amino acids in rendering the toxin inactive in Bacillus thuringiensis, and indicates that the cytolytic potential of the pore forming domain is only realized after proteolytic removal of these residues by proteases in the insect gut. In line with this hypothesis are results obtained with a mutant protein in which Arg28 at the cleavage site was replaced by Asp. This substitution prevented the protein from being cleaved by trypsin in vitro, and reduced its toxicity to M. sexta larvae.

Animals↗

PubMed1995

Expression of giant silkmoth cecropin B genes in tobacco.

Cecropin B is a small antibacterial peptide from the giant silkmoth Hyalophora cecropia. To reveal the potential of this peptide for engineering bacterial disease resistance into crops, several cecropin B gene constructs were made either for expression in the cytosol or for secretion. All constructs were cloned in a plant expression vector and introduced in tobacco via Agrobacterium tumefaciens. A cDNA-derived cecropin B gene construct lacking the amino-terminal signal peptide was poorly expressed in transgenic plants at the mRNA level, whereas plants harbouring a full-length cDNA-derived construct containing the insect signal peptide, showed increased cecropin B-mRNA levels. Highest expression was found in plants harbouring a construct with a plant-gene-derived signal peptide. In none of the transgenic plants could the cecropin B peptide be detected. This is most likely caused by breakdown of the peptide by plant endogenous proteases, since a chemically synthesized cecropin B peptide was degraded within seconds in various plant cell extracts. This degradation could be prevented by the addition of specific protease inhibitors and by boiling the extract prior to adding the peptide. In addition, anionic detergents, in contrast to cationic, zwitter-ionic or non-ionic detergents, could prevent this degradation. Nevertheless, transgenic tobacco plants were evaluated for resistance to Pseudomonas solanacearum, the causal agent of bacterial wilt of many crops, and P. syringae pv. tabaci, the causal agent of bacterial wildfire, which are highly susceptible to cecropin B in vitro. No resistance was found. These experiments indicate that introduction and expression of cecropin B genes in tobacco does not result in detectable cecropin B protein levels and resistance to bacterial infections, most likely due to degradation of the protein by endogenous proteases.

Amino Acid Sequence↗

PubMed1994

Analysis of non-active engineered Bacillus thuringiensis crystal proteins.

Crystal proteins of Bacillus thuringiensis are known for their insecticidal specificity. This specificity is, to a large extent, determined by the interaction of the proteins with high-affinity binding sites on the epithelial membrane of the midgut of sensitive insects. In particular, domain II of the three domains of the toxic moiety has been implicated in specificity. To determine which sequences of the protein are involved in binding, loops of domain II which terminate in the molecular apex of CryIA(b) were replaced by the corresponding regions of CryIE, a protein with different binding characteristics and insect specificity. In contrast to expression of the wild-type genes, expression of the mutant alleles in Escherichia coli resulted in the formation of biologically inactive, insoluble aggregates. Although these aggregates could be solubilized in vitro using urea, in contrast to the wild-type CryIA(b), the mutant proteins did not correctly refold as is shown by their increased protease sensitivity and lack of biological activity. The results indicate that engineering CryI proteins, based on the CryIIIA structure, is likely to prove difficult, particularly since the conformation of CryIIIA and CryI proteins might differ in domain II.

Amino Acid Sequence↗

PubMed1994

Insect resistance of transgenic plants that express modified Bacillus thuringiensis cryIA(b) and cryIC genes: a resistance management strategy.

Tobacco and tomato plants were generated exhibiting insect resistance due to the introduction of modified cryIA(b) and cryIC genes of Bacillus thuringiensis. Limited modifications at selected regions of the coding sequences of both genes are sufficient to obtain resistance against Spodoptera exigua, Heliothis virescens and Manduca sexta. The criteria used to modify both genes demonstrate that the removal of sequence motifs potentially resulting in premature polyadenylation and transcript instability causes increased insect resistance. The expression of a cryIC-cryIA(b) fusion resulting in protection against S. exigua, H. virescens and M. sexta demonstrates the potential of expressing translational fusions, not only to broaden the insect resistance of transgenic plants, but also to simultaneously employ different gene classes in resistance management strategies.

Amino Acid Sequence↗

PubMed1994

Expression of biologically active hordothionins in tobacco. Effects of pre- and pro-sequences at the amino and carboxyl termini of the hordothionin precursor on mature protein expression and sorting.

Hordothionins (HTHs) are small anti-bacterial proteins present in barley endosperm which are processed from larger precursor proteins, consisting of an amino-terminal signal peptide (SP), the mature highly basic HTH and a carboxy-terminal acidic peptide (AP). Different HTH precursor proteins were expressed in tobacco to study the effects of the pre-sequences (SP) and pro-sequences (AP) on expression, processing, sorting and biological activity and hence the feasibility of engineering bacterial disease resistance into crops which lack these proteins. Maximum HTH expression levels of approximately 0.7% (11 mumol/kg) of total soluble protein in young tobacco leaves were obtained using a semi-synthetic gene construct encoding a complete chimaeric HTH precursor protein. Tenfold lower HTH expression levels (maximum 1.3 mumol/kg) were obtained using synthetic gene constructs without the AP-coding sequence and no expression was found in plants containing synthetic HTH gene constructs without SP- and AP-coding sequences. In both cases where expression was found, the precursors were apparently correctly processed, although the HTH produced in plants containing a construct without AP sequence appeared to be slightly modified. No effect on plant phenotype was observed. Localization studies indicated that the HTH was in identical fractions of plants expressing the two different precursors, albeit at a different ratio, and was not secreted into the intercellular spaces of leaves or culture medium by protoplasts. Our results indicated that the AP is not involved in sorting and suggested that it might facilitate transport through membranes. The in vitro toxicity of HTH isolated from transgenic tobacco plants expressing the two different precursor proteins for the bacterial plant pathogen Clavibacter michiganensis subsp. michiganensis appeared similar to that of the HTH purified from barley endosperm.

Amino Acid Sequence↗

PubMed1991

The C-terminal domain of the toxic fragment of a Bacillus thuringiensis crystal protein determines receptor binding.

The insecticidal crystal proteins of Bacillus thuringiensis show a high degree of specificity. In vitro binding studies with several crystal proteins demonstrated a correlation between toxicity and binding to receptors of larval midgut epithelial cells. In order to study the domain-function relationships of the toxic fragment, hybrid crystal proteins based on CryIA(b) and CryIC were constructed. Two out of 11 hybrid proteins constructed exhibited insecticidal activity. Both dispalyed an insecticidal spectrum similar to that of the parental crystal protein from which the C-terminal part of the toxic fragment originated. In addition, in vitro binding studies directly demonstrated the involvement of the C-terminal part of the toxic fragment in receptor binding. These results demonstrate that the C-terminal part of the toxic fragment determines specific receptor binding, which in turn determines, to a large extent, the insect specificity.

Amino Acid Sequence↗

PubMed1990

A Translation Fusion Product of Two Different Insecticidal Crystal Protein Genes of Bacillus thuringiensis Exhibits an Enlarged Insecticidal Spectrum.

Two truncated Bacillus thuringiensis crystal protein genes, belonging to the classes cryIA(b) and cryIC and both coding for insecticidal N-terminal fragments of the corresponding crystal proteins, were translationally fused. Expression of the gene fusion in Escherichia coli showed a biologically active protein with a toxicity spectrum that overlapped those of both contributing crystal proteins.

Journal Article↗

PubMed1990

Insecticidal activity of a bacterial crystal protein expressed by a recombinant baculovirus in insect cells.

Baculoviruses are insect pathogens with a relatively slow speed of action, and this has limited their use as control agents of insect pests. Introduction into baculoviruses of genes which code for proteins interfering specifically with insect metabolism or metamorphosis, such as toxins, hormones, and enzymes, may enhance the pathogenicity of these viruses. The complete insecticidal crystal protein gene cryIA(b) of Bacillus thuringiensis subsp. aizawai 7.21 was engineered into the nuclear polyhedrosis virus of Autographa californica (AcNPV) in place of the polyhedrin gene. In infected Spodoptera frugiperda cells, the cryIA(b) gene was expressed at a high level without interference with AcNPV production. The crystal protein was found in the cytoplasm of S. frugiperda cells, mainly as large crystals with an ultrastructure similar to that of B. thuringiensis crystals. Infected-cell extracts inhibited feeding of the large cabbage white Pieris brassicae. The toxicity of the crystal protein expressed by AcNPV recombinants was comparable with that of the crystal protein expressed by a corresponding Escherichia coli recombinant.

Journal Article↗

PubMed1990

A novel Bacillus thuringiensis gene encoding a Spodoptera exigua-specific crystal protein.

Only one of the four lepidoptera-specific crystal protein subclasses (CryIC) Bacillus thuringiensis was previously shown to be highly toxic against several Spodoptera species. By using a cryIC-derived nucleotide probe, DNA from 25 different strains of B. thuringiensis was screened for the presence of homologous sequences. A putative crystal protein gene, considerably different from the cryIC gene subclass, was identified in the DNA of strain 4F1 (serotype kenyae) and cloned in Escherichia coli. Its nucleotide sequence was determined and appeared to contain several features typical for a crystal protein gene. Furthermore, the region coding for the N-terminal part of the putative toxic fragment showed extensive homology to subclass cryIA sequences derived from gene BtII, whereas the region coding for the C-terminal part appeared to be highly homologous to the cryIC gene BtVI. With an anti-crystal protein antiserum, a polypeptide of the expected size could be demonstrated in Western immunoblots, onto which a lysate of E. coli cells harboring the putative gene, now designated as BtXI, had been transferred. Cells expressing the gene appeared to be equally toxic against larvae of Spodoptera exigua as recombinant cells expressing the BtVI (cryIC)-encoded crystal protein. However, no toxicity against larvae of Heliothis virescens, Mamestra brassicae, or Pieris brassicae could be demonstrated. The nucleotide sequence analysis and the toxicity studies showed that this novel crystal protein gene falls into a new cryl gene subclass. We propose that this subclass be referred to as cryIE.

Amino Acid Sequence↗