Search PubMed⌕ Search

Biomedical subjects

J L Fox

Publications and source records attributed to J L Fox.

At least 181 records · Page 10Linked to original sources
PubMed1989

Gene dosage effect on the expression of the delta-endotoxin genes of Bacillus thuringiensis subsp. kurstaki in Bacillus subtilis and Bacillus megaterium.

Significant differences in expression of the delta-endotoxin genes cryA1 and cryA2 of Bacillus thuringiensis subsp. kurstaki were observed in B. subtilis and B. megaterium. The cryA1 gene was expressed when present on a high-copy-number (hcn) vector in B. megaterium but not in B. subtilis. The cryA2 gene was expressed in both hosts, but at a higher level in B. megaterium. Expression of the cryA2 gene in B. megaterium was better from a hcn vector than from a low copy number vector. Inhibition of sporulation was observed when the toxin genes were present on hcn plasmids in B. subtilis while no such effect was evident in B. megaterium. In addition, there was a significant reduction in copy numbers in both B. subtilis and B. megaterium when delta-endotoxin genes or a spoVG promoter-containing fragment of DNA were cloned into hcn plasmids.

Bacillus↗
PubMed1989

Structure and organization of the gene encoding human pulmonary surfactant proteolipid SP-B.

Human pulmonary surfactant proteolipid SP-B arises by proteolytic processing of a 42,000-dalton precursor. The active proteolipid SP-B is one of two small hydrophobic proteins identified in surfactant that impart surface-active properties to surfactant phospholipids. We report the isolation and characterization of complete SP-B cDNA from a human lung cDNA library. The cDNA was used to isolate the gene encoding the SP-B precursor from a lambda EMBL3 library of human embryonic kidney DNA. The entire SP-B gene was sequenced and is approximately 9.5 kb long, with 11 exons and 10 introns including a large 823-nucleotide 3' untranslated exon. The sequence derived from the exons differs from the cDNA sequence at 3 positions out of 2001, only one of which is in the translated region. Direct RNA sequencing indicated that the 5' untranslated region is only 14 nucleotides long. A number of putative regulatory elements were found upstream of the SP-B gene, including a GC box and several putative cAMP and glucocorticoid receptor binding sites. Several Alu repeats and a region of potential Z-DNA formation were found in the introns. Southern blotting of human genomic DNA probed with SP-B cDNA indicated the presence of only one SP-B gene in the human genome, and the gene was localized to chromosome 2.

Amino Acid Sequence↗
PubMed1989

Platypnea-orthodeoxia and progressive autonomic failure.

Platypnea-orthodeoxia has been described in patients with pulmonary shunts, intracardiac shunts, and severe lung disease. We report a case of platypnea-orthodeoxia in a patient with minimal obstructive lung disease and progressive autonomic failure. We have shown our patient's symptoms to be the result of an orthostatic increase in ventilation-perfusion mismatching and to be corrected with fluid challenge.

Autonomic Nervous System Diseases↗
PubMed1989

Electron probe micro-analysis for subsurface demineralization and remineralization of dental enamel.

A quantitative study of fluoride distribution profile changes in dental enamel was conducted by means of electron probe micro-analysis (EPMA). Fluoride-deposited hydroxyapatite powders were chosen as fluoride standards, and analytical conditions were optimized. The lower limit of detection for fluoride was estimated to be 270 ppm, with an accelerating voltage of 5 kV, a specimen current of 40 nA, and a counting time of 40 seconds. Fluoride profiles in fluoride-treated dental enamel, which exhibited intact surface layers and subsurface demineralization, were determined. The results were also compared with those of an acid-abrasion method, and reasonable consistency was found between these two methods, although the acid-abrasion procedure yielded a slightly lower fluoride content in the initial layers, followed by a higher content of fluoride in the deeper layers. The precision of fluoride profile data obtained from EPMA permits further studies to be conducted on the kinetics of subsurface demineralization and intact surface layer formation ("white spot" formation) which is observed during the acid challenge of dental enamel.

Animals↗
PubMed1989

Quantitative study of fluoride transport during subsurface dissolution of dental enamel.

Previous studies using bovine dental enamel as a model have shown that surface and subsurface dissolution of enamel may be governed by micro-environmental solution conditions. We have now investigated the demineralization phenomenon more rigorously with the primary objective of developing a method for deducing solution species concentration profiles as a function of time from appropriate experimental data. More specifically, in this report, a model-independent method is described for determination of the pore solution fluoride gradients in bovine enamel during subsurface demineralization. Microradiography was used to determine the mineral density profiles, and an electron microprobe technique to determine total fluoride (F) profiles associated with the enamel. In each case, matched sections of bovine enamel were exposed to partially saturated acetate buffers at pH = 4.5 containing 0.5 ppm F for various periods of time (from six to 24 hours). The treated enamel was found to have an intact surface layer and subsurface demineralization. The extent of the demineralization and the depths of the lesions increased with time in all cases. The data were first used to calculate (a) the total F gradients in the enamel at various times, and (b) the local uptake rate of F as a function of time and position. Then, by manipulation of the equations describing the uptake and transport of F, we calculated the pore diffusion rate of F and the micro-environmental solution F concentration in the aqueous pores as a function of time and of distance from the enamel surface. It was also possible to calculate an intrinsic F diffusion coefficient in the pores, which was about 1.0 X 10(-5) cm2/sec, in good agreement with reported values. 14C-sucrose uptake and release experiments with identically prepared demineralized enamel sections were also conducted to provide an independent check on the assumed dependence of porosity on mineral density. The results of this investigation, especially the outcomes relative to this new method for determination of pore solution F gradients during acid attack of the dental enamel, should be valuable in future studies of the mechanism(s) of the action of F in inhibiting dental enamel demineralization.

Animals↗
PubMed1989

Antigens produced by recombinant DNA technology.

Some of the greatest beneficiaries of the revolutionary advances in biotechnology over the past 15 years have been producers of diagnostic reagents, especially for the cloning and expression of antigens, primarily of viral origin. Recombinant DNA technology provides methods for producing antigens for diagnostic assays that are more highly purified, more specific, and safer to produce than viral culture and that are significantly less expensive to manufacture. Antigens so produced can be used for production of antibodies or antisera for competition assays, as reagents for mapping epitopes, as affinity-chromatography ligands for purification of antibodies or protein, and as research reagents. Their initial use in some hepatitis B assays may be primarily a cost-reduction application, but in other applications (e.g., HIV diagnostic tests) they present the first opportunity to commercially produce an otherwise very expensive antigen. Recombinant-DNA-produced antigens are also being used to develop safer vaccines, but not, however, without some consideration of the structural nature of immunodominant epitopes and the adequacy of the immune response.

Antigens↗
PubMed1988

cDNA, deduced polypeptide structure and chromosomal assignment of human pulmonary surfactant proteolipid, SPL(pVal).

In hyaline membrane disease of premature infants, lack of surfactant leads to pulmonary atelectasis and respiratory distress. Hydrophobic surfactant proteins of Mr = 5,000-14,000 have been isolated from mammalian surfactants which enhance the rate of spreading and the surface tension lowering properties of phospholipids during dynamic compression. We have characterized the amino-terminal amino acid sequence of pulmonary proteolipids from ether/ethanol extracts of bovine, canine, and human surfactant. Two distinct peptides were identified and termed SPL(pVal) and SPL(Phe). An oligonucleotide probe based on the valine-rich amino-terminal amino acid sequence of SPL(pVal) was utilized to isolate cDNA and genomic DNA encoding the human protein, termed surfactant proteolipid SPL(pVal) on the basis of its unique polyvaline domain. The primary structure of a precursor protein of 20,870 daltons, containing the SPL(pVal) peptide, was deduced from the nucleotide sequence of the cDNAs. Hybrid-arrested translation and immunoprecipitation of labeled translation products of human mRNA demonstrated an Mr = 22,000 precursor protein, the active hydrophobic peptide being produced by proteolytic processing to Mr = 5,000-6,000. Two classes of cDNAs encoding SPL(pVal) were identified. mRNA of approximately 900 bases was identified on Northern analysis of fetal and adult RNA. Human SPL(pVal) mRNA was more abundant in the adult than in fetal lung. The SPL(pVal) gene locus was assigned to chromosome 8.

Amino Acid Sequence↗
PubMed1988

Microsurgical treatment of ventral (paraclinoid) internal carotid artery aneurysms.

Eight cases of ventral (paraclinoid) internal carotid artery aneurysms are presented. These aneurysms often challenge the surgeon because (a) they are partially or completely obscured by the optic nerve, internal carotid artery, and anterior clinoid process; (b) there is no proximal internal carotid artery control intracranially; and (c) part of the neck and fundus of the aneurysm is located within the cavernous sinus. These aneurysms, which have been classified as separate from the typical carotid-ophthalmic aneurysm group, are illustrated, and their surgical treatment and problems described.

Adult↗
PubMed1988

Central spinal cord injury: magnetic resonance imaging confirmation and operative considerations.

A case of central cervical spinal cord injury, confirmed by magnetic resonance imaging (MRI) and treated by myelotomy, is presented. After recovering well from his central cord syndrome and walking with assistance, the patient developed a rapidly progressive myelopathy beginning 2 months after injury. His main injury localized clinically to the C8, T1 level; but central cord abnormalities were identified 3 months after injury at the C6 level by MRI: a high signal intensity on the proton density sequence and a low-signal intensity on the T1-weighted sequence. At operation 41/2 months after his injury and 1 month after complete paraplegia, a myelotomy at C6 failed to reveal any cavity (syrinx) but instead disclosed only intense gliosis inside a slightly atrophic spinal cord. Rapid clinical improvement ensued. Secondary syringomyelia may be an endstage condition after spinal cord insults that trigger a progressive, pathophysiological reaction leading to central cord necrosis. In selected cases, myelotomy may interrupt this MRI-identified, nosogenic process before cavitation has occurred.

Adult↗
PubMed1988

Petrosal approach for petroclival meningiomas.

Thirteen patients harboring large petroclival meningiomas are reported. The evolution of the petrosal approach is discussed, and modifications for improvement in surgical technique are described. There was no mortality in this series, and total removal was achieved in all but two patients. Morbidity included cranial nerve deficit, pulmonary embolism, and hemiparesis.

Adult↗
PubMed1988

Optic nerve decompression in osteopetrosis.

Osteopetrosis is a rare disorder characterized by generalized increased skeletal density with abnormalities of bone modeling. The skull base is usually involved. Loss of vision with optic nerve atrophy is the most common neurological finding and is traditionally believed to be the result of optic nerve compression within the compromised optic canal. However, retinal degeneration has recently been described and is hypothesized to be the etiology of the visual loss (thus challenging the value of surgical decompression). The authors report their experience with six children suffering from osteopetrosis and severe visual loss. All six patients underwent bilateral microsurgical optic nerve decompression through a supraorbital craniotomy. Improvement in visual acuity occurred postoperatively in five patients, and none had complications. Two technical points are emphasized: 1) optic nerve decompression should be wide and include not only unroofing of the canal but also drilling along both sides of the optic nerve, and 2) the thick, irregular, and highly domed orbital roof should be smoothed down by high-speed drilling to facilitate surgical exposure with minimal retraction of the frontal lobe.

Child↗
PubMed1988

Myelopathic cervical spondylotic lesions demonstrated by magnetic resonance imaging.

Eighteen cases are presented in which magnetic resonance (MR) imaging demonstrated two types of lesions in patients with cervical spondylotic myelopathy. In the first type, localized spinal cord changes at the level of compression, consistent with myelomalacia, were revealed best with T2-weighted images as high-intensity spinal cord signals. In the second type, lesions consistent with either cystic necrosis or secondary syrinx were noted locally, and/or extending longitudinally up, and/or down inside the spinal cord. These latter lesions were best revealed as low-intensity signals on T1-weighted MR images and as a signal-void sign (moving fluid) on proton-density or T2-weighted MR images. It is suggested that segmental lesions at the level of the spondylotic bar represent early proton changes from pressure in and around the same zones that evolve into gray-matter enhancement regions shown as "snake-eyes" on delayed computerized tomography (CT) after myelography. The longitudinal lesions are thought to be the same pencil-shaped zones of cystic necrosis evolving into a secondary syrinx in the late stages (and usually found in the anterior portion of the dorsal columns during delayed CT after myelography). As spinal MR imaging continues to improve, these lesions will be demonstrated more clearly within the cord substance.

Adult↗
PubMed1988

The low incidence of cerebral aneurysms in the Middle East: is it a myth?

It is common belief that there is a relatively low incidence of cerebral aneurysm in the Middle East; however, there are neither routine autopsy studies nor reliable public health data to confirm this impression. We analyzed the clinical data of all patients admitted with a diagnosis of nontraumatic subarachnoid hemorrhage to the King Faisal Specialist Hospital, a modern tertiary medical center in Riyadh, Saudi Arabia. These data were compared with reports from other countries. Although environmental or inherited factors may predispose to a lower incidence of intracranial aneurysm in the Middle East, the true incidence is higher and is not apparent because of the previous referral system for medical care. Medical facilities and expertise are rapidly improving, and future studies undoubtedly will show a higher incidence of intracranial aneurysm.

Adolescent↗
PubMed1987

Synthetic peptides used to locate the alpha-bungarotoxin binding site and immunogenic regions on alpha subunits of the nicotinic acetylcholine receptor.

Synthetic peptides corresponding to 57% of the sequence of alpha subunits of acetylcholine receptors from Torpedo californica electric organ and extending from the NH2 to the COOCH terminus have been synthesized. The alpha-bungarotoxin binding site on denatured alpha subunits was mapped within the sequence alpha 185-199 by assaying binding of 125I-alpha-bungarotoxin to slot blots of synthetic peptides. Further studies showed that residues in the sequence alpha 190-194, especially cysteines-alpha 192, 193, were critical for binding alpha-bungarotoxin. Reduction and alkylation studies suggested that these cysteines must be disulfide linked for alpha-bungarotoxin to bind. Binding sites for serum antibodies to native receptors or alpha subunits were mapped by indirect immunoprecipitation of 125I-peptides. Several antigenic sequences were identified, but a synthetic peptide corresponding to the main immunogenic region (which is highly conformation dependent) was not identified.

Amino Acid Sequence↗
PubMed1987

Crystals of the trp repressor-operator complex suitable for X-ray diffraction analysis.

Crystals of a simulated trp repressor-operator complex have been grown that are large enough and are sufficiently well ordered and durable to provide a high quality molecular image of this regulatory protein X DNA complex to better than 3-A resolution. The "operator" consists of a 2-fold rotationally symmetric 18-base pair duplex that is extended by a dT residue at both 5'-termini. This system exhibits extensive crystal polymorphism. The crystal form and diffraction properties are very sensitive to the length and terminal structure of the operator fragment, as well as the type and concentration of multivalent ions. When combined with the experience reported by others, our results do not support a consistent strategy for crystallization of protein X DNA complexes.

Bacterial Proteins↗