Towards a complete understanding of how a simple eukaryotic cell works.
Explore the source record for details and available documents.
Eukaryotic Cells↗
Biomedical subjects
M Johnston
Publications and source records attributed to M Johnston.
Reliability of the international normalized ratio for monitoring the induction phase of warfarin: comparison with the prothrombin time ratio.
The International Normalized Ratio (INR) was introduced to reduce the variability of prothrombin time (PT) reporting. One potential problem with the use of the INR is the assumption that its reliability is reduced when it is used to monitor patients during the induction phase of treatment. This shortcoming arises because the model used to establish the INR system is based on the use of pooled plasma from patients stabilized on warfarin for at least 6 weeks. Because the prolongation of the PT by warfarin during the induction phase mainly reflects reduction in factor VII levels (whereas the prolongation of the PT after 6 weeks of stabilization reflects reductions in factors X, II, and VII), there exists a potential for loss of accuracy of the INR during warfarin induction. To overcome this potential problem, it has been suggested that the PT ratio should be used to report results during the induction phase of treatment and that the INR system should be reserved for reporting results after the patient has been stabilized. This approach is confusing to the clinician. In addition, the validity of this approach has never been demonstrated in a clinical study. To address this issue, we studied 43 patients for the first 5 days after they started warfarin therapy. We measured the PT in the same plasma samples from each patient with five different commercial thromboplastins. The variance in the PT ratios among the five thromboplastins was compared with the variance obtained with the INR values derived from the PT ratios when using the international sensitivity indexes provided by the manufacturer. Our results indicate that, even during the induction phase, there is less variance with the INR system than with the PT ratio system.
Anticoagulants↗
Laparoscopic myomectomy in the infertile woman.
STUDY OBJECTIVE: To compare the outcome of the procedure we developed for laparoscopic myomectomy with outcomes reported in the literature for open and laparoscopic myomectomies. DESIGN: Prospective trial. SETTING: Lutheran General Hospital, Park Ridge, IL. PATIENTS: Forty-one consecutive infertile women who met selection criteria that were based on our experience with 15 initial laparoscopic myomectomies. INTERVENTION: Laparoscopic myomectomy. MEASUREMENTS AND MAIN RESULTS: Laparoscopic myomectomy was attempted in 41 and completed successfully in 40 women with minimal blood loss. Beyond the single conversion there were no major complications. The pregnancy rate within a year of the procedure was 75% (30 women) and viable term delivery rate was 65% (26 women). CONCLUSIONS: Pregnancy and viable term delivery rates compared favorably with those after open myomectomy procedures. Laparoscopic myomectomy was effective for selected patients experiencing infertility.
Female↗
Reduction of Thermal Spread and Tissue Adherence with an Irrigating Bipolar Grasper
Bipolar energy heats tissues and leads to thermal spread beyond the target tissues. As temperatures rise above 70° C, tissues stick to the metal jaws of the graspers. The use of irrigating fluid while applying the energy should reduce these effects by cooling the surrounding tissues, and also permit the surgeon to clear the operative field of blood. An in vivo animal study was performed to measure these effects. Energy was applied to porcine uterine horn with and without irrigation with a new irrigating bipolar grasper. Lateral thermal spread and tissue adherence were measured. Tissue was excised and thermal spread measured grossly and microscopically. Results are shown in the table. Without irrigation, thermal spread stops at 10 seconds due to complete desiccation of the tissues. Lateral thermal spread is reduced below 10 seconds with irrigation, but it continues to rise as energy is applied. Coagulated tissues adhered to the grasper jaws in all of the nonirrigated tests. Cooling the jaws with irrigation eliminated this. The ability to irrigate through the bipolar grasper improves the surgeon's efficiency by reducing tissue sticking, and adds control by reducing thermal spread during normal application of energy.
Journal Article↗
Distress, expressed emotion, and attributions in relatives of schizophrenia patients.
This article investigates the level of distress in relatives at the time of an acute episode of illness in the schizophrenia sufferer. Guided by attributional literature on the prediction of distress and depression, the association between relatives' distress and their explanations and beliefs concerning the illness is examined in the context of the expressed emotion status of the relative. The study found that although distress levels were unrelated to the relatives' beliefs about the patient's role in negative events, beliefs that illness events were caused by factors internal to the relatives themselves ("self-blaming" beliefs) were associated with distress in the relatives. The authors argue that understanding the cognitive appraisal processes involved in how caregivers perceive schizophrenia is important to understanding their response to the illness and helping them to adapt to the problems.
Acute Disease↗
Drainage of CSF through lymphatic pathways and arachnoid villi in sheep: measurement of 125I-albumin clearance.
We investigated lymphatic drainage pathways of the central nervous system in conscious sheep and quantified the clearance of a cerebrospinal fluid (CSF) tracer into lymph and blood. In the first group of studies, 125I-HSA was injected into the lateral ventricles of the brain or into lumbar CSF and after 6 h, various lymph nodes and tissues were excised and counted for radioactivity. Multiple lymphatic drainage pathways of cranial CSF existed in the head and neck region defined by elevated 125I-HSA in the retropharyngeal/cervical, thymic, pre-auricular and submandibular nodes. Implicated in spinal CSF drainage were mainly the lumbar and intercostal nodes. In a second group of experiments, multiple cervical vessels and the thoracic duct were cannulated and lymph diverted from the animals. Transport of tracer through arachnoid villi was taken from recoveries in venous blood. Following intraventricular administration, the 6 h recoveries of 125I-HSA in the lymph (sum of cervical and thoracic duct) and blood were 8.2% +/- 3.0 and 12.5% +/- 4.5 respectively and at 22 h, 25.1% +/- 6.9 and 20.8% +/- 4.1 respectively. When 125I-HSA was injected into lumbar CSF, the 6 h recoveries of tracer in thoracic duct and blood were 11.6% +/- 2.7 and 16.3% +/- 3.7 respectively. Total lymph and blood recoveries were not significantly different in any experiment. We conclude that the clearance of 125I-HSA from the CSF is almost equally distributed between lymphatic and arachnoid villi pathways.
Animals↗
Two different repressors collaborate to restrict expression of the yeast glucose transporter genes HXT2 and HXT4 to low levels of glucose.
Transcription of the yeast HXT2 and HXT4 genes, which encode glucose transporters, is induced only by low levels of glucose. This low-glucose-induced expression is mediated by two independent repression mechanisms: in the absence of glucose, transcription of both genes is prevented by Rgt1p, a C6 zinc cluster protein; at high levels of glucose, expression of HXT2 and HXT4 is repressed by Mig1p. Only at low glucose concentrations are both repressors inactive, leading to a 10- to 20-fold induction of gene expression. Mig1p and Rgt1p act directly on HXT2 and HXT4 by binding to their promoters. This transcriptional regulation is physiologically very important to the yeast cell because it causes these glucose transporters to be expressed only in low-glucose media, in which they are required for growth.
Base Sequence↗
Rgt1p of Saccharomyces cerevisiae, a key regulator of glucose-induced genes, is both an activator and a repressor of transcription.
The RGT1 gene of Saccharomyces cerevisiae plays a central role in the glucose-induced expression of hexose transporter (HXT) genes. Genetic evidence suggests that it encodes a repressor of the HXT genes whose function is inhibited by glucose. Here, we report the isolation of RGT1 and demonstrate that it encodes a bifunctional transcription factor. Rgt1p displays three different transcriptional modes in response to glucose: (i) in the absence of glucose, it functions as a transcriptional repressor; (ii) high concentrations of glucose cause it to function as a transcriptional activator; and (iii) in cells growing on low levels of glucose, Rgt1p has a neutral role, neither repressing nor activating transcription. Glucose alters Rgt1p function through a pathway that includes two glucose sensors, Snf3p and Rgt2p, and Grr1p. The glucose transporter Snf3p, which appears to be a low-glucose sensor, is required for inhibition of Rgt1p repressor function by low levels of glucose. Rgt2p, a glucose transporter that functions as a high-glucose sensor, is required for conversion of Rgt1p into an activator by high levels of glucose. Grr1p, a component of the glucose signaling pathway, is required both for inactivation of Rgt1p repressor function by low levels of glucose and for conversion of Rgt1p into an activator at high levels of glucose. Thus, signals generated by two different glucose sensors act through Grr1p to determine Rgt1p function.
Bacterial Proteins↗
Two zinc-finger-containing repressors are responsible for glucose repression of SUC2 expression.
Expression of the SUC2 gene in Saccharomyces cerevisiae, which encodes invertase, is repressed about 200-fold by high levels of glucose. Mig1p is a Cys2His2 zinc-finger-containing protein required for glucose repression of SUC2 and several other genes. However, SUC2 expression is still about 13-fold repressed by glucose in a mig1 mutant. We have identified a second repressor, Mig2p, containing zinc fingers very similar to those of Mig1p that is responsible for this remaining glucose repression of SUC2 expression. Overexpression of MIG2 represses SUC2 under nonrepressing conditions, and a LexA-Mig2p fusion represses transcription of a lexO-containing promoter in a glucose-dependent manner, supporting the idea that Mig2p is a glucose-activated repressor. We have shown that Mig2p binds to the Miglp-binding sites in the SUC2 promoter. Even though Mig1p and Mig2p bind to similar sites and share almost identical zinc fingers, they differ in their relative affinities for various Mig1p-binding sites. This could explain our observation that MIG2 appears to have little role in glucose repression of other promoters with MIG1-binding sites.
Amino Acid Sequence↗
Communicating the diagnosis of motor neurone disease.
Communication of the diagnosis of motor neurone disease (MND) is a particularly difficult task for doctors in view of the poor prognosis and the lack of significant treatment. This study examined patients' views of being given the diagnosis and of how it was communicated. Fifty people who had been diagnosed with MND more than six months previously were interviewed about their experience of the diagnosis. The majority reported positive aspects of being told, especially having a label for their condition. The most frequently mentioned critical aspect of how they were told was the directness and clarity with which they were given the information. Patients were more critical if the diagnosis was worse than expected (as it was for most patients) and more satisfied if they felt they had been able to ask questions. There was no evidence that unsatisfactory communications were associated with later mood disturbance. A longitudinal study is recommended to overcome limitations in this cross-sectional design.
Adaptation, Psychological↗
Evaluation of a soluble fibrin assay in patients with suspected pulmonary embolism.
In order to determine the clinical utility of an enzyme immunoassay (EIA) for soluble fibrin in patients with suspected pulmonary embolism (PE), 195 unselected patients with suspected PE underwent blood sampling for measurement of plasma levels of soluble fibrin, and objective testing for PE. A soluble fibrin result of < or = 0.75 micrograms/ml showed a sensitivity of 100% for PE and a specificity of 12.8%, whereas a soluble fibrin result of < or = 1.35 micrograms/ml showed a sensitivity of 90.3% and a specificity of 49.4% for PE. The soluble fibrin assay has potential clinical utility in excluding PE.
Adolescent↗
Free protein S deficiency may be found in patients with antiphospholipid antibodies who do not have systemic lupus erythematosus.
In order to determine if there is a relationship between antiphospholipid antibodies and reduced free protein S levels, we evaluated 21 patients who had an antiphospholipid antibody but had neither a history of venous thromboembolism nor systemic lupus erythematosus (cases) and 55 matched controls, who did not have an antiphospholipid antibody, a history of thrombosis or systemic lupus erythematosus. Cases and controls had similar protein C and antithrombin levels. Six of 21 cases had reduced free protein S antigen levels, compared to 5 of 55 controls (chi 2 = 5.823 p < 0.025). In addition, the mean free protein S level was significantly lower in cases than in controls (0.30 +/- 0.09 units vs 0.39 +/- 0.13 units, p < 0.01, two-tailed Student's t-test). We conclude that antiphospholipid antibodies are associated with a significant decrease in free protein S levels, and that this acquired free protein S deficiency may contribute to the thrombotic diathesis seen in patients with antiphospholipid antibodies.
Adult↗
Isolation of yeast artificial chromosomes free of endogenous yeast chromosomes: construction of alternate hosts with defined karyotypic alterations.
An intrinsic feature of yeast artificial chromosomes (YACs) is that the cloned DNA is generally in the same size range (i.e., approximately 200-2000 kb) as the endogenous yeast chromosomes. As a result, the isolation of YAC DNA, which typically involves separation by pulsed-field gel electrophoresis, is frequently confounded by the presence of a comigrating or closely migrating endogenous yeast chromosome(s). We have developed a strategy that reliably allows the isolation of any YAC free of endogenous yeast chromosomes. Using recombination-mediated chromosome fragmentation, a set of Saccharomyces cerevisiae host strains was systematically constructed. Each strain contains defined alterations in its electrophoretic karyotype, which provide a large-size interval devoid of endogenous chromosomes (i.e., a karyotypic "window"). All of the constructed strains contain the kar1-delta 15 mutation, thereby allowing the efficient transfer of a YAC from its original host into an appropriately selected window strain using the kar1-transfer procedure. This approach provides a robust and efficient means to obtain relatively pure YAC DNA regardless of YAC size.
Chromosomes, Artificial, Yeast↗
Antiphospholipid antibodies and venous thromboembolism.
The clinical relevance of antiphospholipid antibodies (APLA) in patients without systemic lupus erythematosus who have venous thromboembolism (VTE) in unknown. Limited evidence suggests that there is an association between the presence of APLA and both initial and recurrent episodes of VTE and that patients with APLA and VTE are resistant to warfarin therapy. Unselected patients with a first episode of clinically suspected deep vein thrombosis or pulmonary embolism were evaluated with objective tests for VTE and with laboratory tests for APLA; the latter included tests for the lupus anticoagulant (LA) and anticardiolipin antibodies (ACLA). Patients with VTE were treated with anticoagulant therapy and observed during and after discontinuation of anticoagulants for symptomatic recurrence of VTE. There was a strong association between LA and VTE (odds ratio, 9.4; 95% confidence interval [CI], 2.1 to 46.2) and 9 to 65 (14%; 95% CI, 7% to 25%) patients with VTE had LA. There was no association between the presence of ACLA and VTE (odds ratio, 0.7; 95%CI, 0.3 to 1.7) because of the high frequency of positive ACLA assays in patients without VTE. None of the 16 patients with VTE and APLA developed recurrent VTE while receiving warfarin therapy. There was no difference in rates of recurrent VTE in patients with or without APLA after anticoagulant therapy was discontinued. The strong association between LA and VTE suggests that testing for LA in patients with VTE is useful. The measurement of ACLA in patients with VTE has no clinical usefulness because the results are abnormal in a high proportion of patients without VTE. Although the presence of APLA in patients with VTE was not associated with resistance to a conventional intensity of warfarin or an increased risk of recurrent VTE after discontinuation of warfarin, a larger study should address these issues in a subgroup of patients with VTE and LA.
Adolescent↗
INR reporting in Canadian medical laboratories. Thrombosis Interest Group of Canada.
A written survey of all licensed medical laboratories in Canada performing coagulation testing was performed to investigate the level of knowledge and overall usage of the INR system for reporting prothrombin time results in medical laboratories. There was an overall response rate of 857 of 1,228 laboratories surveyed. Fifty-seven percent of responding laboratories utilized some format of INR reporting. The ISI of the individual thromboplastin utilized was known by 89% of laboratories. The ISI of the thromboplastin utilized was known to be specific for the particular reagent/instrument combination in 44% of cases. Fifty-five percent of client physicians preferred PT results to be reported in seconds while 42% desired an INR format. The situation in Canada is similar to the United States in that further education regarding the INR system for PT reporting is required by both medical laboratories and physicians.
Administration, Oral↗
Acquired free protein S deficiency is associated with antiphospholipid antibodies and increased thrombin generation in patients with systemic lupus erythematosus.
In order to determine whether there is a relationship between acquired free protein S deficiency and increased thrombin generation, we performed a cross-sectional study of patients with systemic lupus erythematosus (SLE). Plasma samples were assayed for free protein S and were correlated to levels of prothrombin fragments (F1 + 2); an elevated level of F1 + 2 was used as a surrogate marker for a prothrombotic state. Assays for anticardiolipin antibodies (ACA) and lupus anticoagulant (LA) were performed on two separate blood samples taken at least 3 months apart in order to detect the presence of antiphospholipid antibodies. Of the 36 subjects, 9 had reduced free protein S levels compared to 0 of 21 controls (P = 0.01) and the mean free protein S level was significantly lower in the SLE population than in controls (0.30 +/- 0.08 U/mL versus 0.43 +/- 0.10 U/mL, P < 0.001). Of the 24 subjects with antiphospholipid antibodies, 9 had reduced free protein S levels, compared to 0 of 12 subjects without antiphospholipid antibodies (P = .01). The mean F1 + 2 level was significantly higher in study subjects with reduced free protein S levels than in those with normal free protein S levels (1.22 +/- 0.50 nmol/L versus 0.78 +/- 0.27 nmol/L, P = 0.05). This study confirms an association between antiphospholipid antibodies and reduced free protein S levels and demonstrates that patients with SLE and acquired free protein S deficiency generate more thrombin than patients with SLE and normal free protein S levels. Further studies are needed to determine whether the thrombotic diathesis associated with the presence of antiphospholipid antibodies is directly caused by the concomitant presence of acquired free protein S deficiency.
Adult↗
Variation in odor thresholds for l-carvone and cineole and correlations with suprathreshold intensity ratings.
Specific anosmias have been reported for l-carvone and cineole, two compounds of importance in food flavor perception. Detection thresholds were assessed in groups of 50+ individuals by ascending forced-choice tests conducted in quadruplicate. Wide individual differences in thresholds were observed. Within the same session, threshold correlations were in the range of +0.8 to +0.9, showing good short-term reliability. Correlations with suprathreshold ratings were moderate (in the range of r = -0.5) after subtraction of false positive ratings for blank samples. However, a cineole mixture experiment failed to show any differences between subgroups that were previously classified as high or low sensitivity on the basis of threshold measurements. Re-testing selected groups after a period of months showed considerable within-individual variation in the thresholds, especially for l-carvone. These results call into question the stability and utility of threshold classification for these two compounds.
Adult↗
Three different regulatory mechanisms enable yeast hexose transporter (HXT) genes to be induced by different levels of glucose.
The HXT genes (HXT1 to HXT4) of the yeast Saccharomyces cerevisiae encode hexose transporters. We found that transcription of these genes is induced 10- to 300-fold by glucose. Analysis of glucose induction of HXT gene expression revealed three types of regulation: (i) induction by glucose independent of sugar concentration (HXT3); (ii) induction by low levels of glucose and repression at high glucose concentrations (HXT2 and HXT4); and (iii) induction only at high glucose concentrations (HXT1). The lack of expression of all four HXT genes in the absence of glucose is due to a repression mechanism that requires Rgt1p and Ssn6p. GRR1 seems to encode a positive regulator of HXT expression, since grr1 mutants are defective in glucose induction of all four HXT genes. Mutations in RGT1 suppress the defect in HXT expression caused by grr1 mutations, leading us to propose that glucose induces HXT expression by activating Grr1p, which inhibits the function of the Rgt1p repressor. HXT1 expression is also induced by high glucose levels through another regulatory mechanism: rgt1 mutants still require high levels of glucose for maximal induction of HXT1 expression. The lack of induction of HXT2 and HXT4 expression on high levels of glucose is due to glucose repression: these genes become induced at high glucose concentrations in glucose repression mutants (hxk2, reg1, ssn6, tup1, or mig1). Components of the glucose repression pathway (Hxk2p and Reg1p) are also required for generation of the high-level glucose induction signal for expression of the HXT1 gene. Thus, the glucose repression and glucose induction mechanisms share some of the same components and may share the same primary signal generated from glucose.
Gene Expression↗