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At least 307 records · Page 17Linked to original sources
PubMed2005

Cis-Golgi matrix proteins move directly to endoplasmic reticulum exit sites by association with tubules.

The role of cis-medial Golgi matrix proteins in retrograde traffic is poorly understood. We have used imaging techniques to understand the relationship between the cis-medial Golgi matrix and transmembrane proteins during retrograde traffic in control and brefeldin A (BFA)-treated cells. All five of the cis-medial matrix proteins tested were associated with retrograde tubules within 2-3 min of initiation of tubule formation. Then, at later time points (3-10 min), transmembrane proteins are apparent in the same tubules. Strikingly, both the matrix proteins and the transmembrane proteins moved directly to endoplasmic reticulum (ER) exit sites labeled with p58 and Sec13, and there seemed to be a specific interaction between the ER exit sites and the tips or branch points of the tubules enriched for the matrix proteins. After the initial interaction, Golgi matrix proteins accumulated rapidly (5-10 min) at ER exit sites, and Golgi transmembrane proteins accumulated at the same sites approximately 2 h later. Our data suggest that Golgi cis-medial matrix proteins participate in Golgi-to-ER traffic and play a novel role in tubule formation and targeting.

Animals↗
PubMed1993

Effects of TPA on mitosis of V79 Chinese hamster cells. Reduced precision of chromosome distribution and modification of entrance into and exit out of mitosis.

Protein kinase C (PKC) was activated in V79 Chinese hamster cells with 10 nM 12-O-tetradecanoylphorbol-13-acetate (TPA). Within 30 min soluble activity decreased concomitant with a 10-fold increase of particulate activity. The latter was still elevated after 3 h but was back to control levels after 24 h of treatment; by then soluble activity was lost. The frequency of mitotic cells with signs of abnormal spindle function increased within 15 min and reached a plateau after 45-60 min which lasted throughout the 4 h treatment. The c-mitotic effect was delayed and significantly lower when 10 nM TPA was combined with 50 microM of the protein kinase inhibitor H7. The frequency of disturbed mitotic cells decreased after 24 h of treatment but remained significantly higher than in non-treated cells. Change of medium and addition of new TPA caused a slight but significant further increase. It is suggested that PKC takes part in eliciting the c-mitotic effect of TPA. However, the sustained effect coincident with down-regulation points to significant alterations of the level or the activity of an as yet unidentified ultimate elicitor. TPA also caused a transient block in the G2 phase which was ameliorated by H7 and which could not be detected at all in TPA-pretreated cells (24 h) given new TPA. This suggests that PKC takes part in eliciting the G2/M block as well but the mechanism is different from the one(s) behind the c-mitotic effect. V79 cells were found to exit from mitosis in the presence of 0.2 microgram/ml of colcemid but TPA-pretreated cells showed a decreased exit rate. There was no sign of hampered exit among cells going into mitosis soon after the G2 block was reversed, which implies that the spontaneous reversal of the block does not involve rapid down-regulation of PKC.

Animals↗
PubMed1979

Coupling interval, exit block, and periodicity of ventricular parasystolic rhythm.

The electrocardiograms in this study of parasystolic rhythm were tape recorded and then analysed with a special purpose hybrid computer. The rate of appearance of specific inter-ectopic intervals was shown to change significantly with small changes in either the sinus or parasystolic pacemaker period. Natural changes in the period of the ectopic pacemakers were observed over several hours. Changes amounting to 14% within 10 min and 18% overall were observed in one patient, and a gradual lengthening of 10% over 3 h in another. A previously undescribed form of exit block has been discovered in one patient where the block remained active for a given time only after propagation from the parasystolic focus. Different interectopic intervals were shown to contribute to specific and restricted coupling interval locations in diastole. Hence this form of exit block, by preventing some inter-ectopic intervals from propagating, limited the locations in diastole in which parasystolic ectopic complexes could appear. In this case later diastolic complexes were inhibited and hence fusion complexes were completely absent. Parasystolic rhythm, with and without the exit block described, was simulated successfully by a digital computer. The simulations aided our understanding of the clinical data.

Aged↗
PubMed2000

Residual Cdc2 activity remaining at meiosis I exit is essential for meiotic M-M transition in Xenopus oocyte extracts.

To investigate the regulatory mechanisms of the cell cycle transition from M phase to M phase in meiotic cycles, a Xenopus oocyte extract that performs the M-M transition has been developed. Using the meiotic extract, we found that a low level of Cdc2 activity remained at the exit of meiosis I (MI), due to incomplete degradation of cyclin B. The inactivation of the residual Cdc2 activity induced both entry into S phase and tyrosine phosphorylation on Cdc2 after MI. Quantitative analysis demonstrated that a considerable amount of Wee1 was present at the MI exit and Cdc2 inhibitory phosphorylation during this period was suppressed by the dominance of Cdc2 over Wee1. Consistently, the addition of more than a critical amount of Wee1 to the extract induced Cdc2 inhibitory phosphorylation, changing the M-M transition into an M-S-M transition. Thus, the Cdc2 activity remaining at MI exit is required for suppressing entry into S phase during the meiotic M-M transition period.

Animals↗
PubMed2000

Nud1p links astral microtubule organization and the control of exit from mitosis.

The budding yeast spindle pole body (SPB) not only organizes the astral and nuclear microtubules but is also associated with a number of cell-cycle regulators that control mitotic exit. Here, we describe that the core SPB component Nud1p is a key protein that functions in both processes. The astral microtubule organizing function of Nud1p is mediated by its interaction with the gamma-tubulin complex binding protein Spc72p. This function of Nud1p is distinct from its role in cell-cycle control: Nud1p binds the spindle checkpoint control proteins Bfa1p and Bub2p to the SPB, and is part of the mitotic exit network (MEN) in which it functions upstream of CDC15 but downstream of LTE1. In conditional lethal nud1-2 cells, the MEN component Tem1p, a GTPase, is mislocalized, whereas the kinase Cdc15p is still associated with the SPB. Thus, in nud1-2 cells the failure of Tem1p to interact with Cdc15p at the SPB probably prevents mitotic exit.

Animals↗
PubMed2000

Saccharomyces cerevisiae BUB2 prevents mitotic exit in response to both spindle and kinetochore damage.

The spindle assembly checkpoint-mediated mitotic arrest depends on proteins that signal the presence of one or more unattached kinetochores and prevents the onset of anaphase in the presence of kinetochore or spindle damage. In the presence of either damage, bub2 cells initiate a preanaphase delay but do not maintain it. Inappropriate sister chromatid separation in nocodazole-treated bub2 cells is prevented when mitotic exit is blocked using a conditional tem1(c) mutant, indicating that the preanaphase failure in bub2 cells is a consequence of events downstream of TEM1 in the mitotic exit pathway. Using a conditional bub2(tsd) mutant, we demonstrate that the continuous presence of Bub2 protein is required for maintaining spindle damage-induced arrest. BUB2 is not required to maintain a DNA damage checkpoint arrest, revealing a specificity for spindle assembly checkpoint function. In a yeast two-hybrid assay and in vitro, Bub2 protein interacts with the septin protein Cdc3, which is essential for cytokinesis. These data support the view that the spindle assembly checkpoint encompasses regulation of distinct mitotic steps, including a MAD2-directed block to anaphase initiation and a BUB2-directed block to TEM1-dependent exit.

Cell Cycle↗
PubMed2001

The Spo12 protein of Saccharomyces cerevisiae: a regulator of mitotic exit whose cell cycle-dependent degradation is mediated by the anaphase-promoting complex.

The Spo12 protein plays a regulatory role in two of the most fundamental processes of biology, mitosis and meiosis, and yet its biochemical function remains elusive. In this study we concentrate on the genetic and biochemical analysis of its mitotic function. Since high-copy SPO12 is able to suppress a wide variety of mitotic exit mutants, all of which arrest with high Clb-Cdc28 activity, we speculated whether SPO12 is able to facilitate exit from mitosis when overexpressed by antagonizing mitotic kinase activity. We show, however, that Spo12 is not a potent regulator of Clb-Cdc28 activity and can function independently of either the cyclin-dependent kinase inhibitor (CDKi), Sic1, or the anaphase-promoting complex (APC) regulator, Hct1. Spo12 protein level is regulated by the APC and the protein is degraded in G1 by an Hct1-dependent mechanism. We also demonstrate that in addition to localizing to the nucleus Spo12 is a nucleolar protein. We propose a model where overexpression of Spo12 may lead to the delocalization of a small amount of Cdc14 from the nucleolus, resulting in a sufficient lowering of mitotic kinase levels to facilitate mitotic exit. Finally, site-directed mutagenesis of highly conserved residues in the Spo12 protein sequence abolishes both its mitotic suppressor activity as well as its meiotic function. This result is the first indication that Spo12 may carry out the same biochemical function in mitosis as it does in meiosis.

Amino Acid Sequence↗
PubMed1991

Epidemiology of CAPD-associated peritonitis caused by coagulase-negative staphylococci: comparison of strains isolated from hands, abdominal Tenckhoff catheter exit site and peritoneal fluid.

We identified twenty patients maintained on continuous ambulatory peritoneal dialysis who suffered repeated episodes of peritonitis caused by coagulase-negative staphylococci. We documented hand and exist-site coagulase-negative staphylococcus-associated peritonitis over a total period of 32 months, and compared hand and exit-site strains with strains isolated from dialysate fluid using three typing methods: biotyping using the API Staph kit plus antibiograms, immunoblotting using sera raised in rabbits to three standard strains of coagulase-negative staphylococci, and 35S-methionine-labelled coagulase-negative staphylococcal profiles separated on sodium dodecylsulphate polyacrylamide gel electrophoresis and visualised by autoradiography (radioPAGE). In 5 of 84 episodes, strains isolated from skin were indistinguishable by all three typing methods from the dialysate strain. In a further two episodes, hand or exit-site isolates were indistinguishable by all three typing methods from the dialysate strain isolated in the subsequent, but not the same, episode. Thus in the majority of episodes, no inference of hand or exit-site origin of dialysate infection could be drawn.

Adult↗
PubMed1995

Exit rounds: a reflection exercise.

This paper questions the long-held assumption that "experience is the best teacher". Reflection, it is argued, is the element that turns experience into learning. Unfortunately, reflection is the experiential learning skill in which student are most deficient. Further, clinical teachers may not appreciate the reciprocal and synergistic relationship of experience and reflection, and therefore they may not exploit its full potential. This paper argues for the formal and explicit use of reflection to clinical teaching. In addition to providing a theoretical rationale for the use of reflection is learning, one example of a reflection exercise--exit rounds--is described. Exit rounds focus on recently discharged patients and provide students with an opportunity to reflect on what they have learned from working with these patients. In addition to being a learning exercise, exit rounds provide attending physicians with an opportunity to address emotional issues, to evaluate students' learning and performances, to deal with "housekeeping" details, and to provide closure.

Clinical Competence↗
PubMedDate not supplied

Image-guided coaxial fine needle aspiration biopsy with a side-exiting guide.

PURPOSE: The aim of this study was to evaluate the diagnostic accuracy and complication rates of a side-exiting coaxial needle system for fine needle aspiration (FNA) biopsies. METHOD: Between 1995 and 1998, 127 nonconsecutive biopsies were performed on 122 patients (74 males, 48 females). CT guidance was used in 111, ultrasound guidance was used in 14, and both were used in 2 biopsies. Patient history, biopsy site, needle performance, complications, and cytology results were recorded. RESULTS: Diagnostic rate and accuracy were 92.9 and 99.2%, respectively. There were minor complications from 14 biopsies, and all of them arose from chest biopsies: pneumothorax in 13 of 47 and hemoptysis in 1 of 47. There were no major complications. CONCLUSION: The side-exiting coaxial needle system is a safe and effective alternative to the conventional end-exiting coaxial needle system for performance of image-guided FNA biopsies.

Biopsy, Needle↗
PubMedDate not supplied

Comparison of native versus nonnative English-speaking nurses on critical thinking assessments at entry and exit.

Diversity of language among healthcare employees and nursing students is growing as diversity increases among the general population. Institutions have begun to develop systems to accommodate diversity and to assimilate workers. One barrier to nonnative English-speaking nurse hires may be posed by readiness for the licensure exam and the critical thinking assessments that are now an expected outcome of nursing programs, and act as a gatekeeper to graduation and to employment. To assist in preparing for high-stakes testing, the Assessment Technologies Institute Critical Thinking Assessment was developed in compliance with credentialing bodies' educational outcomes criteria. This pilot study of 209 nursing students was designed to reveal any possible language bias that might act as a barrier to nonnative English speakers. Nursing students were entered as whole classes to the study to control for selection bias. A sample representative of national nursing enrollment was obtained from 21 universities, with 192 (92%) native English-speaking students and 17 (8%) nonnative English speakers participating in the study. All students were given the Assessment Technologies Institute Critical Thinking Assessment at entry and exit to their nursing program. Average scores on entry were 66% for nonnative speakers and 72% for native speakers. At exit, the nonnative speakers had closed the gap in academic outcomes. They had an average score of 72% compared to 73% for native speakers. The study found that the slight differences between the native and nonnative speakers on 2 exit outcome measures-National Council licensure examination (NCLEX-RN) pass rates and Critical Thinking Assessment-were not statistically significant, demonstrating that nonnative English speakers achieved parity with native English-speaking peers on the Critical Thinking Assessment tool, which is often believed to be related to employment readiness.

Bias↗
PubMed2002

Identification of a new APC/C recognition domain, the A box, which is required for the Cdh1-dependent destruction of the kinase Aurora-A during mitotic exit.

The mitotic kinase Aurora A (Aur-A) is required for formation of a bipolar mitotic spindle and accurate chromosome segregation. In somatic cells, Aur-A protein and kinase activity levels peak during mitosis, and Aur-A is degraded during mitotic exit. Here, we investigated how Aur-A protein and kinase activity levels are regulated, taking advantage of the rapid synchronous cell division cycles of Xenopus eggs and cell-free systems derived from them. Aur-A kinase activity oscillates in the early embryonic cell cycles, just as in somatic cells, but Aur-A protein levels are constant, indicating that regulated activation and inactivation, instead of periodic proteolysis, is the dominant mode of Aur-A regulation in these cell cycles. Cdh1, the APC/C activator that targets many mitotic proteins for ubiquitin-dependent proteolysis during late mitosis and G1 in somatic cells, is missing in Xenopus eggs and early embryos. We find that addition of Cdh1 to egg extracts undergoing M phase exit is sufficient to induce rapid degradation of Aur-A. Aur-A contains both of the two known APC/C recognition signals, (1) a C-terminal D box similar to those required for ubiquitin-dependent destruction of cyclin B and several other mitotic proteins, and (2) an N-terminal KEN box similar to that found on cdc20, which is ubiquitinated in response to APC/C(Cdh1). The D box is required for Cdh1-induced destruction of Aur-A but the KEN box is not. Destruction also requires a short region in the N terminus, which contains a newly identified recognition signal, the A box. The A box is conserved in vertebrate Aur-As and contains serine 53, which is phosphorylated during M phase. Mutation of serine 53 to aspartic acid, which can mimic the effect of phosphorylation, completely blocks Cdh1-dependent destruction of Aur-A. These results suggest that dephosphorylation of serine 53 during mitotic exit could control the timing of Aur-A destruction, allowing recognition of both the A box and D box by Cdh1-activated APC/C.

3T3 Cells↗
PubMed1998

Position of exit X-rays from rotated-inclined double-crystal monochromators.

The rotated-inclined double-crystal monochromator (RIDCM) has been adopted to reduce the heat load from third-generation undulator radiation. The position of the exit X-rays from RIDCM has been calculated as a function of X-ray energy on the basis of diffraction theory including refraction effects. The results show that the positions of the exit X-rays vary over a wide range due to asymmetric reflection. Methods of fixing the exit position in RIDCM are also discussed.

Journal Article↗
PubMed1998

Micro X-ray diffraction analysis of thin films using grazing-exit conditions.

An X-ray diffraction technique using a hard X-ray microbeam for thin-film analysis has been developed. To optimize the spatial resolution and the surface sensitivity, the X-ray microbeam strikes the sample surface at a large glancing angle while the diffracted X-ray signal is detected with a small (grazing) exit angle. Kirkpatrick-Baez optics developed at the Photon Factory were used, in combination with a multilayer monochromator, for focusing X-rays. The focused beam size was about 10 x 10 micro m. X-ray diffraction patterns of Pd, Pt and their layered structure were measured. Using a small exit angle, the signal-to-background ratio was improved due to a shallow escape depth. Under the grazing-exit condition, the refraction effect of diffracted X-rays was observed, indicating the possibility of surface sensitivity.

Journal Article↗
PubMed1997

A study of the efficacy of dressings in preventing infections of continuous ambulatory peritoneal dialysis catheter exit sites.

This paper describes a preliminary investigation into the efficacy of dressings in preventing catheter exit site infections in patients undergoing continuous ambulatory peritoneal dialysis (CAPD). It has been carried out in the form of a pilot study. The background to the study is described and the literature is reviewed. This revealed that it is an important field of research. Exit site infections are the main cause of morbidity and treatment failure in CAPD patients. The rationale for carrying the study out, the findings and the implications for further study are reported and discussed. There is little guidance in current literature for clinicians on the prevention of catheter exit site infection. Patients are difficult to recruit to research studies. Practising nurses need training and careful management as data collectors.

Bandages↗
PubMed1995

Mechanism of image formation for thick biological specimens: exit wavefront reconstruction and electron energy-loss spectroscopic imaging.

With increasing frequency, cellular organelles and nuclear structures are being investigated at high resolution using electron microscopic tomography of thick sections (0.3-1.0 microns). In order to reconstruct the structures in three dimensions accurately from the observed image intensities, it is essential to understand the relationship between the image intensity and the specimen mass density. The imaging of thick specimens is complicated by the large fraction of multiple scattering which gives rise to incoherent and partially coherent image components. Here we investigate the mechanism of image formation for thick biological specimens at 200 and 300 keV in order to resolve the coherent scattering component from the incoherent (multiple scattering) components. Two techniques were used: electron energy-loss spectroscopic imaging (ESI) and exit wavefront reconstruction using a through-focus series. Although it is commonly assumed that image formation of thick specimens is dominated by amplitude (absorption) contrast, we have found that for conventionally stained biological specimens phase contrast contributes significantly, and that at resolutions better than approximately 10 nm, superposed phase contrast dominates. It is shown that the decrease in coherent scattering with specimen thickness is directly related to the increase in multiple scattering. It is further shown that exit wavefront reconstruction can exclude the microscope aberrations as well as the multiple scattering component from the image formation. Since most of the inelastic scattering with these thick specimens is actually multiple inelastic scattering, it is demonstrated that exit wavefront reconstruction can act as a partial energy filter. By virtue of excluding the multiple scattering, the 'restored' images display enhanced contrast and resolution. These findings have direct implications for the three-dimensional reconstruction of thick biological specimens, where a simple direct relationship between image intensity and mass density was assumed, and the aberrations were left uncorrected.

Chromatin↗
PubMed2004

Cdt1 and geminin are down-regulated upon cell cycle exit and are over-expressed in cancer-derived cell lines.

Licensing origins for replication upon completion of mitosis ensures genomic stability in cycling cells. Cdt1 was recently discovered as an essential licensing factor, which is inhibited by geminin. Over-expression of Cdt1 was shown to predispose cells for malignant transformation. We show here that Cdt1 is down-regulated at both the protein and RNA level when primary human fibroblasts exit the cell cycle into G0, and its expression is induced as cells re-enter the cell cycle, prior to S phase onset. Cdt1's inhibitor, geminin, is similarly down-regulated upon cell cycle exit at both the protein and RNA level, and geminin protein accumulates with a 3-6 h delay over Cdt1, following serum re-addition. Similarly, mouse NIH3T3 cells down-regulate Cdt1 and geminin mRNA and protein when serum starved. Our data suggest a transcriptional control over Cdt1 and geminin at the transition from quiescence to proliferation. In situ hybridization and immunohistochemistry localize Cdt1 as well as geminin to the proliferative compartment of the developing mouse gut epithelium. Cdt1 and geminin levels were compared in primary cells vs. cancer-derived human cell lines. We show that Cdt1 is consistently over-expressed in cancer cell lines at both the protein and RNA level, and that the Cdt1 protein accumulates to higher levels in individual cancer cells. Geminin is similarly over-expressed in the majority of cancer cell lines tested. The relative ratios of Cdt1 and geminin differ significantly amongst cell lines. Our data establish that Cdt1 and geminin are regulated at cell cycle exit, and suggest that the mechanisms controlling Cdt1 and geminin levels may be altered in cancer cells.

Animals↗
PubMed2006

Gonococci exit apically and basally from polarized epithelial cells and exhibit dynamic changes in type IV pili.

Type IV pili are a major virulence factor of the obligate human pathogen Neisseria gonorrhoeae (the gonococcus; Gc). Pili facilitate bacterial adherence to epithelial cells, but their participation in later steps of epithelial infection, particularly intracellular replication and exit, is poorly understood. Using polarized T84 cells as a model for mature mucosal epithelia, pilus dynamics in piliated, Opa-expressing Gc were examined over time. T84 infection was characterized by a several-hour delay in the growth of cell-associated bacteria and by non-directional exit of Gc, the first time these phenomena have been reported. During infection, non-piliated progeny arose stochastically from piliated progenitors. Piliated and non-piliated Gc replicated and exited from T84 cell monolayers equally well, demonstrating that piliation did not influence Gc survival during epithelial infection. The frequency with which pilin variants arose from a defined piliated progenitor during T84 cell infection was found to be sufficiently high to account for the extensive pilin variation reported during human infection. However, the repertoire of variants appearing in association with T84 cells was similar to what was seen in the absence of cells, demonstrating that polarized epithelial cells can support Gc replication without selecting for a subset of pilin variants or piliation states.

Bacterial Adhesion↗