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Biomedical subjects

G Thomas

Publications and source records attributed to G Thomas.

At least 523 records · Page 29Linked to original sources
PubMed1992

Cloning of six new genes with zinc finger motifs mapping to short and long arms of human acrocentric chromosome 22 (p and q11.2).

Zinc finger genes encode proteins containing tandemly repeated zinc-mediated folded structures that are found in several transcriptional regulatory proteins. To identify new zinc finger genes, we have screened at low stringency human cosmid libraries enriched in chromosome 22 sequences with a probe derived from the finger region of the mouse Kruppel-like gene, mKr2. We identified 23 nonoverlapping human cosmids cross-hybridizing with the probe. All sequences obtained from cosmid subclones hybridizing with the probe revealed Kruppel-type consensus sequences. Hybridizations to somatic cell hybrid panels and to metaphase chromosomes revealed that 2 nonoverlapping zinc finger cosmids map to chromosome 22p and 4 map to 22q11.2. The 17 other nonoverlapping cosmids most likely map to other chromosomes. The short arms of acrocentric chromosomes are thought to encode only ribosomal RNA genes. Therefore, the identification of two zinc finger genes on chromosome 22p represents an unexpected finding of unknown significance. The four zinc finger genes that map to 22q11.2 are within the cat eye and DiGeorge syndrome regions and thus provide us with potential candidate genes for these developmental malformations.

Amino Acid Sequence↗
PubMed1992

Rapid isolation of cosmids from defined subregions by differential Alu-PCR hybridization on chromosome 22-specific library.

A method based on the differential screening of a chromosome-specific cosmid library with amplified inter-Alu sequences obtained from a set of somatic cell hybrids has been developed to target the isolation of probes from predefined subchromosomal regions. As a model system, we have used a chromosome 22-specific cosmid library and four cell hybrids containing different parts of this chromosome. The procedure has identified cosmids that demonstrate differential hybridization signals with Alu-PCR products from these cell hybrids. We show, by in situ hybridization or individual mapping, that their hybridization pattern is indicative of their sublocalization on chromosome 22, thus resulting in a large enrichment factor for the isolation of probes from specific small chromosome subregions. Depending on the local Alu-sequence density, from 3 to 10 independent loci per megabase of genome can thus be identified.

Animals↗
PubMed1992

The activity of single-agent carboplatin in advanced seminoma.

Between 1982 and 1990, 70 patients with advanced metastatic seminoma were treated with 4-6 courses of single-agent carboplatin (SAC) administered at 400 mg/m2 every 3-4 weeks. Treatment was of low toxicity and no patients suffered neurotoxicity, ototoxicity or significant renal damage. There was only one episode of neutropenic sepsis and no thrombocytopenic bleeding. The median follow-up of surviving patients was 3 years. 16 patients have relapsed and 4 of these 16 have died, thus the actuarial 3-year relapse-free survival was 77% (95% CI 65-86%), cause-specific survival was 94% (95% CI 82-99%) and overall survival was 91% (95% CI 80-96%). The risk of relapse was reduced by post-chemotherapy irradiation (PCRT) to involved nodes, occurring in 1/20 patients treated with PCRT compared with 11/31 who could have been treated but were not (P = 0.04). Of the 16 patients who relapsed, 12(75%) have been salvaged with combination chemotherapy and remain free from further relapse with a median follow-up of 18 months. Though this level of survival is equivalent to that obtained with initial cisplatin-based combination chemotherapy, the recurrence rate indicates that SAC remains an investigative treatment, except for unfit patients.

Adult↗
PubMed1992

Contrast enhancing lymph nodes in bladder cancer: a potential pitfall on CT.

We report three cases of bladder cancer in which contrast enhanced computed tomography (CT) demonstrated minimally enlarged lymph nodes. These showed uniform uptake of contrast medium to a similar degree as adjacent venous structures, making the distinction between vessels and lymph nodes difficult. Magnetic resonance imaging (MRI) examination resolved the problem in two of the three patients.

Carcinoma, Transitional Cell↗
PubMed1992

Increased p53 protein content of colorectal tumours correlates with poor survival.

Allelic losses on the short arm of chromosome 17 occur frequently in colorectal cancers. Despite the existence of other common molecular events such as loss of the long arms of chromosomes 18 and 5, it has been demonstrated that the former has the greatest prognostic significance. Of the various genes mapping to the commonly deleted sequence, the best candidate as a 'target' seems to be the p53 antioncogene. We applied our methods of detection of the p53 protein in a series of 78 colorectal cancers stored in a tumour bank from 1985 to 1989, for which the median follow-up was 42 months. Nuclear-attached p53 was quantified by flow cytometry and soluble p53 was assayed by ELISA. Both assays used a monoclonal antibody considered to be specific for a conformational epitope present only on the mutated protein. Fifty of the 78 tumours (64%) were found to present significant levels of p53 attached to the nucleus. A further two tumours contained high levels of p53 only in their soluble fraction. Thus, 52 out of 78 cancers (67%) were considered to be positive for p53. The p53 content correlated with 17p loss (P < 0.002), hyperdiploid DNA content (P < 0.001) and tumour site (P < 0.03), but not Dukes' stage (P = 0.15). p53 negative cases had a better overall survival than p53 positive ones (P < 0.03). When the 14 stage D tumours were excluded from the analysis, p53 was no longer significantly predictive of survival (P < 0.07), but remained predictive of recurrence (P < 0.02) and metastasis (P < 0.03). Multivariate analysis was not performed because of the small number of cases. Overall, disease-free and metastasis-free survival were compared to the positivity obtained either with pAb 421 and/or 1801 or pAb 240 since all three were used in the flow cytometric analysis, defining subsets of 421-, 1801+ and 421-, 1801-, 240+. The presence of nuclear protein presenting the mutation-specific epitope, recognised by pAb 240, was found to be the most discriminant. It must be noted that univariate survival analysis demonstrated that more than 80% of patients with p53-negative tumours were alive at 3 years vs less than 50% in the p53-positive group. A large prospective study should be conducted to define the exact prognostic significance of the p53 content of colorectal carcinomas.

Adenocarcinoma↗
PubMed1992

Base sequence criteria and Cartesian coordinates for stable B/Z and B/Z/B junctions in relaxed DNA.

It seems increasingly evident that if the Z form of DNA exists in the genome it must exist as short sections of alternating pyrimidine-purine sequences in the midst of very long sections of B-form DNA. We have determined the minimum length of a string of alternating CG base pairs that can go into the Z form in the middle of a long B form. Self-complimentary oligomers of the form T(M)(CG)(N)A(M) were synthesized. The conformation of the resulting duplex was determined in 6M aqueous NaCl solution by Raman scattering. We have found that 12 alternating CG base pairs is the minimum length required to form a stable Z form of DNA inside of a long B form section. Only the 4 center CG base pairs go into the Z form. These 4 CG base pairs in the Z form are flanked on each side by 4 CG base pairs in a non-Z (probably B) form as well as the ..TT.. ..AA.. sequences in the B form. We propose a model of the B/Z junction in which the double helix flips directly from the B form to the Z form so that there are no base pairs in the junction. In this model the B form is nucleated in the AT base pairs on each end and is propagated into the CG base pairs in the center. This model is supported by isotopic H/D exchange experiments that shows that the H/D exchange of the non-Z form CG base pairs is highly retarded and indicates that they remain in the B form. A Thermodynamic analysis of the concentration dependence of the melting point of the duplexes in both low and high salt, supports our model and rules out the possibility of hairpin formation. The enthalpy for the formation of a B/Z junction is determined to be about +16 kcal/junction. A comparison of these results with recent results on B/Z junctions in super-coiled DNA is given. Molecular modeling calculations permit us to obtain values for the coordinates and torsional angles of the oligomers showing both B/Z and B/Z/B junctions. The Cartesian coordinates for these oligomers as well as stereo figures of these models in color are available from the authors.

Base Sequence↗
PubMed1992

Hemorrhagic cystitis with herpes simplex virus type 2 in the bladder mucosa.

A 67-year-old woman who had underlying rheumatoid arthritis and diabetes mellitus had an 8-year history of recurrent hemorrhagic cystitis. During her most recent episode of cystitis, a specimen of urine yielded herpes simplex virus type 2 in culture. A biopsy of the bladder mucosa revealed intranuclear inclusions in multinucleated and mononuclear giant cells that were positive for herpes simplex virus type 2 by immunoperoxidase staining. She had no evidence of infection with herpes simplex virus outside her bladder.

Aged↗
PubMed1992

Endothelin-1 induces a histamine-dependent flare in vivo, but does not activate human skin mast cells in vitro.

The role of the mast cell in endothelin-1 induced flare has been investigated by in vivo and in vitro experiments. The intradermal injection of endothelin-1 (10 pmol) into human skin induced a pallor with surrounding axon-reflex flare which is similar to the flare response to histamine (1 nmol). At these doses, chosen to give identical flare areas, blood flow was increased in the area of the endothelin-induced flare over a longer period. A systemic H1-receptor antagonist significantly inhibited the area of both flares, although blood flow in the remaining portion of the endothelin-induced flare remained raised. Endothelin-1 at concentrations up to 3 x 10(-5) M failed to release histamine from human dispersed skin mast cells. We suggest from these results that a major component of endothelin-1 induced flare results from mast cell activation that is secondary to direct stimulation of sensory nerves by the peptide.

Adult↗
PubMed1992

Mammalian subtilisin-related proteinases in cleavage activation of the paramyxovirus fusion glycoprotein: superiority of furin/PACE to PC2 or PC1/PC3.

The fusion glycoprotein precursor of Newcastle disease virus is ubiquitously cleaved in the constitutive secretory pathway if it possesses an oligobasic cleavage motif (RRQR/KR), whereas the precursor is refractory to cleavage if the motif is monobasic (GR/KQGR). We examined the cleavage activity of the mammalian subtilisin-related proteinases furin/PACE, PC2, and PC1/PC3, which are thought to be responsible for proprotein processing in either the constitutive (furin/PACE) or the regulated (PC2 and PC1/PC3) secretory pathway, for the viral precursors with different cleavage motifs. Only furin/PACE was fully capable of cleaving the precursors with the oligobasic motif. PC2 and PC1/PC3 were incapable or only partially capable of cleaving at this motif. None of the proteinases cleaved the monobasic motif. These results suggest involvement of furin/PACE in viral protein processing in the constitutive secretory pathway.

Amino Acid Sequence↗
PubMed1992

Screening of microdeletions of chromosome 20 in patients with Alagille syndrome.

We report a cytogenetic and molecular study of a series of patients with Alagille syndrome. All 14 patients were studied with high resolution banding techniques and eight of them were also analysed with non-radioactive in situ hybridisation of the cosmid probe D20S6. Seven of these eight patients were also studied for allelic losses at the D20S6 locus. No microdeletion of chromosome 20 was found in this series.

Alagille Syndrome↗
PubMed1992

Estimation of erythropoietin secretion rate in normal and uremic subjects.

We have developed a method for directly estimating the secretion rate of endogenous erythropoietin (EPO) in human subjects. Carrier-free recombinant human EPO was labeled with 125I by the chloramine T method. Human serum albumin was then added prior to removal of free iodide. Seven normal subjects and nine patients with chronic uremia and anemia were studied. Each subject received a bolus of 125I-EPO according to body size and then a constant infusion for 5 h. Secretion rate was calculated as the rate of infusion divided by serum EPO specific activity given by the protein-bound counts divided by the EPO concentration. Serum EPO concentration was significantly higher in the patients than the controls (mean 30.9 pg/ml vs. 11.1 pg/ml, P < 0.05), although all values were within the normal range. Mean EPO secretion rate was 255 in the patients (range 68-1,101) and 190 pg.kg-1 x h-1 in the normal group (range 52-382). This difference was not significant. As the subjects were in a steady state, EPO disappearance/degradation was the same in patients compared with controls despite a relatively hypoplastic marrow.

Adult↗
PubMed1992

Brief ischemia-reperfusion induces stunning of endothelium in canine coronary artery.

BACKGROUND: Brief ischemic episodes that induce stunning of the myocardium may also induce stunning of the coronary endothelium. To test this hypothesis, we examined both in vivo and in vitro responses of canine coronary arteries exposed to brief ischemia. METHODS AND RESULTS: Functional recovery of the endothelium was examined in vivo during reperfusion after 15 minutes of ischemia. Vasodilatory responses to acetylcholine were severely impaired during the first hour of reperfusion but gradually improved over a 90-minute period after ischemia. The vasoconstrictive response to U46619 was enhanced for the first 30 minutes of reperfusion and returned to normal within 60 minutes. In vitro vasomotor responses to potassium chloride, acetylcholine, bradykinin, and sodium nitroprusside were examined in isolated segments of canine coronary arteries preexposed in vivo to brief ischemia (10-30 minutes) and 20 minutes of reperfusion. The results showed enhanced contractile responses and blunted endothelium-dependent but not endothelium-independent vasodilatory responses of arterial rings subjected to 10 minutes of ischemia. Twenty and 30 minutes of ischemia completely impaired endothelium-dependent vasodilation. When reperfusion was extended to 120 minutes after 15 minutes of ischemia, vasodilatory responses to acetylcholine had recovered by almost 90%. Examination of endothelial integrity by transmission electron microscopy after 10-15 minutes of ischemia revealed no evidence of structural damage. Twenty and 30 minutes of ischemia induced cytoplasmic vacuolation, partial detachment of endothelium, and swelling of cytoplasmic organelles. CONCLUSIONS: These data support the hypothesis that brief ischemia-reperfusion induces stunning of endothelium in which endothelium-dependent vasodilatory function is impaired temporarily without morphological damage.

Acetylcholine↗
PubMed1992

Surveillance after orchidectomy for patients with clinical stage I nonseminomatous testis tumors.

PURPOSE: This study was designed to determine the proportion of patients with clinical stage I nonseminomatous germ cell tumors of the testis (NSGCTT) managed with surveillance after orchidectomy who have more advanced disease and, therefore, require further treatment, the time to progression, the sites of progression, and the efficacy of treatment delayed until progression was recognized. PATIENTS AND METHODS: One hundred five patients were observed prospectively without further treatment after orchidectomy and full clinical staging. Treatment was given immediately upon detection of marker-positive, clinical, or radiologic evidence of disease. RESULTS: Thirty-seven patients (35.2%) have required further therapy for disease progression, occurring from 2 to 21 months after diagnosis. Thirty-six patients have been successfully treated. Overall, 104 patients (99%) remain alive and free of disease at 12 to 121 months after orchidectomy. Progression occurred in the retroperitoneum in 25 of 37 patients who developed further disease on surveillance. The presence of vascular invasion in the primary tumor was predictive of an increased risk of progression. CONCLUSION: Surveillance is a valid alternative to immediate retroperitoneal lymph node dissection in patients with clinical stage I NSGCTT but should be recommended only under the close supervision of physicians experienced in the diagnosis and treatment of testicular cancer.

Adolescent↗
PubMed1992

Multiple tumor suppressor genes in multistep carcinogenesis.

One of the most exciting areas of molecular oncology is the convergence of two independent lines of evidence suggesting involvement of multiple tumor suppressor genes in a given type of cancer. First, epidemiology and somatic cell genetics indicate the presence of multiple tumor suppressor genes in each of several malignancies. Second, cancers often lose multiple chromosomal regions during tumor progression. We will use two tumors, colorectal cancer and Wilms tumor, to illustrate the questions that multiple tumor suppressor genes raise.

Colorectal Neoplasms↗
PubMed1992

Improved power control during microwave heating in biological applications.

The heating performance of prototype variable power control units attached to two domestic microwave ovens, 500 W and 700 W, was investigated. The units employed the phase control method where rated voltage was obtained by switching AC supply at a particular angular position on the sinusoidal voltage. In order to create experimental conditions employed in a previous study, Sydney tap water (50 mL) was heated at a 10% power level in the 500 W oven. Water boiled at 10 min in both experiments. However, the precision and control of the heating was greatly improved with addition of the control unit. A disinfecting solution (50 mL) and a tissue fixative (10 mL) were included for experiments with the 700 W oven. A power level of only 1% was sufficient to maintain the temperature of the fixative at low temperatures (30-40 degrees C) where many biological reactions occur. The present results indicate that microwave heating power can be controlled by the variable power control method. This will make temperature control possible through the provision of an electronic feedback loop which links a thermocouple with the power control unit.

Heating↗