Mutations in translation initiation factors lead to increased rates of deadenylation and decapping of mRNAs in Saccharomyces cerevisiae

The turnover of most mRNAs in Saccharomyces cerevisiae begins with deadenylation followed by decapping and 5'-->3' exonucleolytic digestion. An important question involves the mechanisms that allow particular mRNAs to exhibit different rates of both deadenylation and decapping. Since the cap structure plays a critical role in the assembly of translation initiation factors, we hypothesized that the status of the cytoplasmic cap binding complex would affect the rate of decapping. To test this hypothesis, we examined mRNA decay rates in yeast strains that were defective in several translation initiation factors that are part of the cap binding complex. These experiments yielded three significant observations. First, any mutation known to inhibit translation initiation also increased the rate of decapping. Second, decapping still occurred only after deadenylation, suggesting that the ability of the poly(A) tail to inhibit decapping does not require efficient translation of the transcript. Third, mutants with defects in translation initiation factors also showed an increase in the rate of deadenylation, suggesting that the rate of deadenylation may be controlled primarily by the translation status of the transcript. These results argue that the nature of the translation initiation complex is a critical factor in determining the mRNA half-life. This view also implies that some cis-acting sequences that modulate mRNA decay rate do so by affecting the translation status of the transcript.

Chainsaw size for delimbing

New Zealand loggers commonly use chainsaws weighing up to 10 kg. Chainsaw work is both physically arduous and potentially dangerous. A contributing factor to the high injury rate of loggers could be the high physiological and biomechanical load of chainsaw work. This study investigated the comparative cardiovascular strain imposed on 11 chainsaw operators when delimbing (cutting branches) with chainsaws of small, medium and large capacity under controlled conditions. Chainsaw operator cardiovascular strain increased with greater chainsaw weight and was associated with two chainsaw operator anthropometric dimensions (arm length and bent elbow height).

SPET brain perfusion imaging in mild traumatic brain injury without loss of consciousness and normal computed tomography

We present SPET brain perfusion findings in 32 patients who suffered mild traumatic brain injury without loss of consciousness and normal computed tomography. None of the patients had previous traumatic brain injury, CVA, HIV, psychiatric disorders or a history of alcohol or drug abuse. Their ages ranged from 11 to 61 years (mean = 42). The study was performed in 20 patients (62%) within 3 months of the date of injury and in 12 (38%) patients more than 3 months post-injury. Nineteen patients (60%) were involved in a motor vehicle accident, 10 patients (31%) sustained a fall and three patients (9%) received a blow to the head. The most common complaints were headaches in 26 patients (81%), memory deficits in 15 (47%), dizziness in 13 (41%) and sleep disorders in eight (25%). The studies were acquired approximately 2 h after an intravenous injection of 740 MBq (20.0 mCi) of 99Tcm-HMPAO. All images were acquired on a triple-headed gamma camera. The data were displayed on a 10-grade colour scale, with 2-pixel thickness (7.4 mm), and were reviewed blind to the patient's history of symptoms. The cerebellum was used as the reference site (100% maximum value). Any decrease in cerebral perfusion in the cortex or basal ganglia less than 70%, or less than 50% in the medial temporal lobe, compared to the cerebellar reference was considered abnormal. The results show that 13 (41%) had normal studies and 19 (59%) were abnormal (13 studies performed within 3 months of the date of injury and six studies performed more than 3 months post-injury). Analysis of the abnormal studies revealed that 17 showed 48 focal lesions and two showed diffuse supratentorial hypoperfusion (one from each of the early and delayed imaging groups). The 12 abnormal studies performed early had 37 focal lesions and averaged 3.1 lesions per patient, whereas there was a reduction to--an average of 2.2 lesions per patient in the five studies (total 11 lesions) performed more than 3 months post-injury. In the 17 abnormal studies with focal lesions, the following regions were involved in descending frequency: frontal lobes 58%, basal ganglia and thalami 47%, temporal lobes 26% and parietal lobes 16%. We conclude that: (1) SPET brain perfusion imaging is valuable and sensitive for the evaluation of cerebral perfusion changes following mild traumatic brain injury; (2) these changes can occur without loss of consciousness; (3) SPET brain perfusion imaging is more sensitive than computed tomography in detecting brain lesions; and (4) the changes may explain a neurological component of the patient's symptoms in the absence of morphological abnormalities using other imaging modalities.

mRNA surveillance in eukaryotes: kinetic proofreading of proper translation termination as assessed by mRNP domain organization?

In the last few years it has become clear that a conserved mRNA degradation system, referred to as mRNA surveillance, exists in eukaryotic cells to degrade aberrant mRNAs. This process plays an important role in checking that mRNAs have been properly synthesized and functions, at least in part, to increase the fidelity of gene expression by degrading aberrant mRNAs that, if translated, would produce truncated proteins. A critical issue is how normal and aberrant mRNAs are distinguished and how that distinction leads to differences in mRNA stability. Recent results suggest a model with three main points. First, mRNPs have a domain organization that is, in part, a reflection of the completion of nuclear pre-mRNA processing events. Second, the critical aspect of distinguishing a normal from an aberrant mRNA is the environment of the translation termination codon as determined by the organization of the mRNP domains. Third, the cell distinguishes proper from improper termination through an internal clock that is the rate of ATP hydrolysis by Upf1p. If termination is completed before ATP hydrolysis, the mRNA is protected from mRNA degradation. Conversely, if termination is slow, then ATP hydrolysis and a structural rearrangement occurs before termination is completed, which affects the fate of the terminating ribosome in a manner that fails to stabilize the mRNA. This proposed system of distinguishing normal from aberrant transcripts is similar to, but distinct from other systems of kinetic proofreading that affect the accuracy of other biogenic processes such as translation accuracy and spliceosome assembly.

Gestational bleeding, bacterial vaginosis, and common reproductive tract infections: risk for preterm birth and benefit of treatment

OBJECTIVE

To examine associations between bacterial vaginosis and other prevalent lower genital tract infections and clinically recognized first-trimester bleeding; possible independent and joint effects of gestational bleeding and bacterial vaginosis or other prevalent infections on preterm birth and premature rupture of membranes; and effects of antimicrobial treatment on reducing risks of preterm birth among these women.

METHODS

A secondary analysis was conducted of 1100 pregnant women enrolled in a prospective observational study that examined the effects of standardized diagnosis and treatment of lower genital tract infections to prevent preterm birth.

RESULTS

Sixty percent of women with first-trimester bleeding had one or more study infections detected at the initial examination. First-trimester bleeding was associated independently with the presence of bacterial vaginosis (odds ratio [OR] 1.5, 95% confidence interval [CI] 1.0, 2.3), Trichomonas vaginalis (OR 2.3, 95% CI 1.3, 4.2), and Chlamydia trachomatis (OR 2.7, 95% CI 1.4, 5.1). Preterm birth was increased among women with first-trimester bleeding and bacterial vaginosis (relative risk [RR] 4.4, 95% CI 2.0, 9.5) and bacterial vaginosis and T vaginalis (RR 3.0, 95% CI 1.0, 8.8). Systemic antimicrobial treatment reduced the rate of preterm birth among women with bacterial vaginosis without first-trimester bleeding (RR 0.37, 95% CI 0.16, 0.88). Treatment of women with both first-trimester bleeding and bacterial vaginosis reduced preterm birth (RR 0.52, 95% CI 0.18, 1.55), but not significantly.

CONCLUSION

First-trimester bleeding was increased among women with bacterial vaginosis, T vaginalis, C trachomatis, and combinations of these infections. Women with bacterial vaginosis who also experienced first-trimester bleeding were at heightened risk for preterm birth. Treatment of studied infections reduced significantly the risks of preterm birth among women without first-trimester bleeding.

Analysis of mutations in the yeast mRNA decapping enzyme

A major mechanism of mRNA decay in yeast is initiated by deadenylation, followed by mRNA decapping, which exposes the transcript to 5' to 3' exonucleolytic degradation. The decapping enzyme that removes the 5' cap structure is encoded by the DCP1 gene. To understand the function of the decapping enzyme, we used alanine scanning mutagenesis to create 31 mutant versions of the enzyme, and we examined the effects of the mutations both in vivo and in vitro. Two types of mutations that affected mRNA decapping in vivo were identified, including a temperature-sensitive allele. First, two mutants produced decapping enzymes that were defective for decapping in vitro, suggesting that these mutated residues are required for enzymatic activity. In contrast, several mutants that moderately affected mRNA decapping in vivo yielded decapping enzymes that had at least the same specific activity as the wild-type enzyme in vitro. Combination of alleles within this group yielded decapping enzymes that showed a strong loss of function in vivo, but that still produced fully active enzymes in vitro. This suggested that interactions of the decapping enzyme with other factors may be required for efficient decapping in vivo, and that these particular mutations may be disrupting such interactions. Interestingly, partial loss of decapping activity in vivo led to a defect in normal deadenylation-dependent decapping, but it did not affect the rapid deadenylation-independent decapping triggered by early nonsense codons. This observation suggested that these two types of mRNA decapping differ in their requirements for the decapping enzyme.

The cis acting sequences responsible for the differential decay of the unstable MFA2 and stable PGK1 transcripts in yeast include the context of the translational start codon

A general pathway of mRNA turnover has been described for yeast in which the 3' poly(A) tail is first deadenylated to an oligo(A) length, leading to decapping and subsequent 5'-3' exonucleolytic decay. The unstable MFA2 mRNA and the stable PGK1 mRNAs both decay through this pathway, albeit at different rates of deadenylation and decapping. To determine the regions of the mRNAs that are responsible for these differences, we examined the decay of chimeric mRNAs derived from the 5' untranslated, coding, and 3' untranslated regions of these two mRNAs. These experiments have led to the identification of the features of these mRNAs that lead to their different stabilities. The MFA2 mRNA is unstable solely because its 3' UTR promotes the rates of deadenylation and decapping; all other features of this mRNA are neutral with respect to mRNA decay rates. The PGK1 mRNA is stable because the sequence context of the PGK1 translation start codon and the coding region function together to stabilize the transcript, whereas the PGK13' UTR is neutral with respect to decay. Importantly, changes in the PGK1 start codon context that destabilized the transcript also reduced its translational efficiency. This observation suggests that the nature of the translation initiation complex modulates the rates of mRNA decapping and decay.

Analysis of mRNA decay pathways in Saccharomyces cerevisiae

The analysis of mRNA turnover often requires a knowledge of the pathway by which a particular mRNA is being degraded. In this article we describe experimental procedures that can be used to determine the mechanism of degradation for yeast transcripts. These approaches include the insertion of strong secondary structures to block exonuclease cleavage and thereby trap decay intermediates. In addition, mRNA decay pathways can be analyzed by using regulatable promoters to perform transcriptional pulse-chase experiments, thereby allowing the determination of precursor-product relationships during the mRNA decay process. Finally, the mechanism of mRNA degradation can also now be determined by using trans-acting mutations specific for distinct mRNA turnover pathways. Most importantly, the combination of these three approaches can often clearly define the mechanism(s) by which a given transcript is degraded.

Regional variations in endothelin-1 and its receptor subtypes in human coronary vasculature: pathophysiological implications in coronary disease

Endothelin-1 is a potent vasoconstrictor peptide and mitogen for vascular smooth muscle cells. Increased plasma or tissue levels of endothelin-1 have been described after myocardial infarction and in atherosclerosis, suggesting that this peptide may play a pathophysiological role in various coronary syndromes. Here, we have studied regional variations in ET-1 and its receptors in control and atherosclerotic human coronary vasculature using standard immunohistochemistry and in vitro autoradiography. ET-1 immunoreactivity was associated with luminal endothelial cells and smooth muscle cells at regions of atherosclerosis. ET(A) receptors were present on smooth muscle cells of coronary arteries and on cardiac myocytes. Medial ET(B) receptor binding at the proximal region of coronary arteries was weak, but increased significantly towards distal regions of this vessel (p<0.005 in control and p<0.0005 in ischaemic heart disease). Microvascular endothelial cells in the adventitia of coronary arteries, myocardial microvessels and the endocardial endothelium expressed the ET(B) receptor exclusively. The receptor variations revealed in this study provide supporting evidence that ET-1 is associated with (1) vascular smooth muscle and endothelial cell proliferation, including areas of intimal hyperplasia and regions of neovascularization (2) increased ET-1-induced reactivity of distal portions of the human coronary artery, (3) ET-1-mediated constriction of myocardial microvessels. These results provide new insights into different potential roles for this peptide in healthy and diseased human coronary vasculature.

Pulmonary vasoconstriction induced by mitral valve obstruction in sheep

We hypothesized that left atrial hypertension results in pulmonary vasoconstriction, which is obscured by the expected passive decrease in pulmonary vascular resistance. The objectives of this study were to demonstrate and quantify the vasoconstrictive changes that occur in the pulmonary circulation during experimental left atrial hypertension, to determine the site of vasoconstriction, and to explore its mechanism. Sheep were instrumented for measurement of pulmonary arterial (Ppa), left atrial (Pla), and systemic arterial pressures (Psa) with a Foley balloon catheter to variably obstruct the mitral valve. Distal pulmonary arterial wedge pressure (Ppaw) was determined by using a 5-Fr Swan-Ganz catheter that was advanced until it wedged with the balloon deflated. Cardiac output (CO) was estimated by thermodilution; pulmonary vascular resistances (PVR) were calculated as mean (Ppa - Pla)/CO = total PVR, (Ppa - Ppaw)/CO = upstream PVR, and (Ppaw - Pla)/CO = downstream PVR. We studied 15 awake sheep at baseline and during increases in Pla of 10 and 20 cmH2O, with and without inhalation of approximately 36 parts per million of nitric oxide. Left atrial hypertension resulted in elevation of Ppa. CO decreased only slightly at both levels of Pla elevation. Nitric oxide inhalation caused a significant decrease in PVR, which was greater as Pla increased. This vasodilator effect was most striking in downstream vessels. Experiments with phentolamine, atropine, and ibuprofen failed to reveal the mechanism of the reactive pulmonary vasoconstriction.

Optimal management of amiodarone therapy: efficacy and side effects

OBJECTIVES

To review management and dosing guidelines for amiodarone therapy, and discuss the drug's adverse event profile.

METHODS

Review of relevant studies and reports.

RESULTS

Amiodarone is a highly effective antiarrhythmic drug, but is associated with adverse effects involving several organs. Amiodarone-induced arrhythmia is rare, with frequency of 0.3% in one study. Pulmonary toxicity is the most serious noncardiac side effect (2-17% of patients). Hypersensitivity pneumonitis can appear early in the course of therapy. Interstitial pneumonitis is a more common but insidious pulmonary reaction characterized by cough, low-grade fever, and dyspnea that occurs after months or years of therapy. Clinically important hypothyroidism and hyperthyroidism occur in 2-10% of patients. Optic neuritis or neuropathy in which patients experience decreased or blurred vision may progress to permanent blindness. Abnormalities in liver function tests, especially elevated aminotransferase and alkaline phosphatase levels, are seen in 4-25% of patients. Neurologic side effects were reported in 20-40% of patients, at times associated with tremor, ataxia, peripheral neuropathy, malaise or fatigue, sleep disturbances, dizziness, and headaches. Several types of dermatologic reactions have been reported, including allergic rash, photosensitivity, and blue-gray skin discoloration. The best strategy for early detection of pulmonary toxicity is vigilant clinical follow-up with monitoring of cardiac status and liver and thyroid function, and prescription of the lowest effective dosage. After an initial loading dose, 200 mg/day in many patients maintains arrhythmia control and minimizes the frequency of side effects.

CONCLUSION

Amiodarone is a safe and efficacious antiarrhythmic agent when lower dosages are given to patients who are closely monitored and subject to careful follow-up.

Angiotensin II mediates systemic rebound hypertension after cessation of prostacyclin infusion in sheep

Prostacyclin (or epoprostenol), an arachidonic acid metabolite, is an effective treatment for patients with primary pulmonary hypertension. Interruption of chronic prostacyclin infusion can result in recurrent symptoms of dyspnea and fatigue. The etiology of this phenomenon is unknown. We hypothesized that sympathoadrenal activation could lead to increased vascular tone after abrupt termination of the infusion. To evaluate this effect, we monitored six chronically instrumented, awake sheep during and after infusion of prostacyclin. Prostacyclin decreased mean arterial pressure (MAP) by 14% and increased cardiac output by 33%. After the infusion ceased, MAP rebounded 23% above baseline, and cardiac output decreased by 28% from peak values within 10 min. We were unable to demonstrate an increase in norepinephrine levels after cessation of prostacyclin, nor did alpha-adrenergic blockade affect postinfusion hemodynamics. However, plasma renin activity increased >10-fold at peak infusion and remained elevated for up to 2 h after discontinuation of prostacyclin. Coinfusion of the angiotensin II-receptor antagonist L-158,809 resulted in complete abrogation of the postcessation rise in MAP. We conclude that renin-angiotensin system activation is primarily responsible for systemic hypertension occurring after abrupt cessation of prostacyclin infusion in sheep and that angiotensin II receptor blockade prevents this response. Our data do not support a role for sympathetic nervous system activation in the systemic pressor response after prostacyclin infusion.

'Killing the angel in the house': creativity, femininity and aggression

The author brings to bear an art historical perspective on the psychoanalytic understanding of creativity as an object relationship, proposing that the creative endeavour is determined by a wider, more complex network of internal and external object relationships than is usually assumed. The workings of tradition, language, contemporary practices, methods and materials are explored. Creative block is considered in the context of the determining relationships, with particular reference to the role of aggression. The position of the latter within psychoanalytic theories of creativity is surveyed and it is proposed that aggression has a pivotal place not primarily in instituting sublimation, reparation or reaction formation but simply because the processes of creativity demand it. Virginia Woolf's image of 'Killing the Angel in the House' is analysed and used to track the implications of gender, focusing on the concept of the muse. It is pointed out that traditionally, the fear, guilt and anxiety associated with aggressive creativity has been mediated by the muse, which is compared to the internal good object. Drawing on art history, artists' statements, and clinical material, the author illustrates the disparate means by which the presence of 'muse' can be internalised to infuse the relationships that constitute creativity.

Isolation and characterization of Dcp1p, the yeast mRNA decapping enzyme

A major mechanism of mRNA decay occurs by the process of deadenylation, decapping and 5' --> 3' exonucleolytic degradation. Recently, the product of the DCP1 gene has been shown to be required for decapping mRNAs in vivo and co-purifies with decapping activity in vitro. We have purified Dcp1p to homogeneity and shown that it is sufficient for decapping, thereby indicating that Dcp1p is the decapping enzyme. Characterization of Dcp1p activity in vitro indicated that the 7-methyl group of the cap structure contributes to the enzyme's substrate specificity. In addition, Dcp1p was effectively inhibited by uncapped mRNAs, and the enzyme efficiently cleaved substrates that were >/=25 nucleotides in length, with a preference for longer mRNA substrates. These properties suggest that Dcp1p recognizes the mRNA substrate by interactions with both the cap and the RNA moiety. The Dcp1p is also a phosphoprotein, suggesting its activity may be regulated by post-transcriptional modification.

Evidence for the embryonic origin of partial chromosome 7 deletion in monozygotic twins with juvenile chronic myelogenous leukemia

During donor evaluation for allogeneic bone marrow transplantation (BMT) of a 28-month-old child with juvenile chronic myelogeneous leukemia (JCML) with 46,XY,-7,+mar karyotype, the potential donor twin brother was found to be thrombocytopenic. Subsequent genotype analysis determined monozygosity with 98% probability. Bone marrow analysis of the twin brother revealed the same 46,XY,-7,+mar karyotype and a diagnosis of JCML was made. Metaphase FISH studies documented that mar chromosome in both twins contains the pericentromeric region of chromosome 7 and thus both twins had a partial monosomy of chromosome 7. A possible embryonic origin of del(7) is proposed.

Analysis of the yeast genome: identification of new non-coding and small ORF-containing RNAs

The genome sequences from increasing numbers of organisms allow for rapid and organized examination of gene expression. Yet current computational-based paradigms for gene recognition are limited and likely to miss genes expressing non-coding RNAs or mRNAs with small open reading frames (ORFs). We have utilized two strategies to determine if there are additional transcripts in the yeast Saccharomyces cerevisiae that were not identified in previous analyses of the genome. In one approach, we identified strong consensus polymerase III promoters based on sequence, and determined experimentally if these promoters drive the expression of an RNA polymerase III transcript. This approach led to the identification of a new, non-essential 170 nt non-coding RNA. An alternative strategy analyzed RNA expression from large sequence gaps>2 kb between predicted ORFs. Fifteen unique RNA transcripts ranging in size from 161 to 1200 nt were identified from a total of 59 sequence gaps. Several of these RNAs contain unusually small potential ORFs, while one is clearly non-coding and appears to be a small nucleolar RNA. These results suggest that there are likely to be additional previously unidentified non-coding RNAs in yeast, and that new paradigms for gene recognition will be required to identify all expressed genes from an organism.

Population-based research data as a means to address health outcomes

Health care restructuring efforts have been influenced by changes in public policy, payment mechanisms, and societal values. In today's environment, leading issues focus on quality and cost-effective care. Health care systems are moving from a concentration on structures and processes of care to an expanded view that encompasses the exploration, documentation, and improvement of patient outcomes. This article presents an overview of the domains of health outcomes, widely used surveys in the measurement of outcomes, methodological issues related to interpreting outcome measures, and trends for clinical practice and future research.

The effect of allograft meniscal replacement on intraarticular contact area and pressures in the human knee. A biomechanical study

To define the biomechanical effects of total lateral meniscectomy and of subsequent lateral meniscal allograft replacement on load transmission and distribution across the human knee, we mounted 10 fresh-frozen young human cadaveric knees on a mechanical testing system. Peak pressure and contact area profiles were determined at 0 degrees, 30 degrees, and 60 degrees of knee flexion using pressure-sensitive film and a densitometer. Load transmission profiles were determined for each knee in a sequential test order: 1) intact knee, 2) after lateral meniscectomy, 3) after implantation of size-matched meniscal allograft fixed with bone plugs, and 4) after release of the anterior and posterior horn attachments of the allograft. Total lateral meniscectomy resulted in a 45% to 50% decrease in total contact area. Allograft replacement increased total contact area by 42% to 65% as compared with total meniscectomy at all flexion angles. After release of the anterior and posterior horn attachments, contact area was identical to that after total meniscectomy. Total lateral meniscectomy resulted in a 235% to 335% increase in peak local contact pressure. Allograft replacement decreased these pressures by 55% to 65% at all flexion angles, but they remained significantly greater than those in the intact state. After release of the anterior and posterior horn attachments, contact pressures were identical to those after total meniscectomy. Compared with total meniscectomy, meniscal allograft transplantation significantly increases contact area and decreases peak local contact pressures, but any biomechanical advantages are lost without bone plug fixation of the anterior and posterior horns.

Self-administration of drugs by older people

Medications are often dispensed in hospital on a drug round, regardless of whether this is the best time for the individual patient. Drug rounds do not enable patients to learn about their medications while in hospital. Self-administration of medication allows patients to receive education about their medications and increases the chances of compliance.

Oxaliplatin, tetraplatin, cisplatin, and carboplatin: spectrum of activity in drug-resistant cell lines and in the cell lines of the National Cancer Institute's Anticancer Drug Screen panel

The present study was designed to explore the activity of platinum compounds in cisplatin-resistant cell lines, the unselected cell lines of the National Cancer Institute's Anticancer Drug Screen, and the potential for use in combination. The activities of four platinum compounds in cisplatin-resistant KB and A2780 cells were investigated. The cells were highly resistant to cisplatin and cross-resistant to carboplatin, but less than one-tenth as resistant to oxaliplatin and tetraplatin. Cellular accumulation of all platinum compounds was decreased in both resistant cell lines. When the activities of cisplatin and oxaliplatin were evaluated in the National Cancer Institute's Anticancer Drug Screen, marked differences were observed. Evaluation of the activity profile using the COMPARE program revealed a different pattern for both agents: the cisplatin activity profile was similar to those of other diamine-platinum compounds, alkylating agents including melphalan, and camptothecin analogs, whereas the activity profile of oxaliplatin resembled those of other "dach" (diaminocyclohexane) platinum compounds and of acridine derivatives. The sensitivity profiles are influenced by the target(s)/mechanism(s) of action and the mechanism(s) of resistance of a drug. The dissimilarity in profiles suggests that these two platinum compounds have a different target(s)/mechanism(s) of action, a different mechanism(s) of resistance, or most likely both. Studies evaluating combinations of cisplatin/oxaliplatin suggest that the activities of these two agents are at least additive and possibly synergistic. Oxaliplatin has a different spectrum of activity and low cross-resistance to cisplatin and should be valuable in cisplatin refractory patients or in combination with cisplatin.