4,417 research outputs found
Dithizone Staining of Intracellular Zinc: An Unexpected and Versatile Counterscreen for Auxotrophic Marker Genes in Saccharomyces cerevisiae
Auxotrophic marker genes such as URA3, LEU2, and HIS3 in Saccharomyces cerevisiae have long been used to select cells that have been successfully transformed with recombinant DNA. A longstanding challenge in working with these genes is that counterselection procedures are often lacking. This paper describes the unexpected discovery of a simple plate assay that imparts a bright red stain to cells experiencing nutritional stress from the lack of a marker gene. The procedure specifically stains a zinc-rich vesicular compartment analogous to the zinc-rich secretory vesicles found in insulin-secreting pancreatic islet cells and glutamate-secreting neurons. Staining was greatly diminished in zap1 mutants, which lack a homeostatic activator of zinc uptake, and in cot1 zrc1 double mutants, which lack the two yeast homologs of mammalian vesicle-specific zinc export proteins. Only one of 93 strains with temperature-sensitive alleles of essential genes exhibited an increase in dithizone staining at its non-permissive temperature, indicating that staining is not simply a sign of growth-arrested or dying cells. Remarkably, the procedure works with most commonly used marker genes, highlights subtle defects, uses no reporter constructs or expensive reagents, requires only a few hours of incubation, yields visually striking results without any instrumentation, and is not toxic to the cells. Many potential applications exist for dithizone staining, both as a versatile counterscreen for auxotrophic marker genes and as a powerful new tool for the genetic analysis of a biomedically important vesicular organelle
Decoupling of the Antiferromagnetic and Insulating States in Tb doped Sr2IrO4
Sr2IrO4 is a spin-orbit coupled insulator with an antiferromagnetic (AFM)
transition at TN=240 K. We report results of a comprehensive study of
single-crystal Sr2Ir1-xTbxO4. This study found that mere 3% (x=0.03)
tetravalent Tb4+(4f7) substituting for Ir4+ (rather than Sr2+) completely
suppresses the long-range collinear AFM transition but retains the insulating
state, leading to a phase diagram featuring a decoupling of magnetic
interactions and charge gap. The insulating state at x=0.03 is characterized by
an unusually large specific heat at low temperatures and an incommensurate
magnetic state having magnetic peaks at (0.95, 0, 0) and (0, 0.95, 0) in the
neutron diffraction, suggesting a spiral or spin density wave order. It is
apparent that Tb doping effectively changes the relative strength of the SOI
and the tetragonal CEF and enhances the Hund's rule coupling that competes with
the SOI, and destabilizes the AFM state. However, the disappearance of the AFM
accompanies no metallic state chiefly because an energy level mismatch for the
Ir and Tb sites weakens charge carrier hopping and renders a persistent
insulating state. This work highlights an unconventional correlation between
the AFM and insulating states in which the magnetic transition plays no
critical role in the formation of the charge gap in the iridate.Comment: 8 figure
Right ventricular dysfunction after resuscitation predicts poor outcomes in cardiac arrest patients independent of left ventricular function.
OBJECTIVE: Determination of clinical outcomes following resuscitation from cardiac arrest remains elusive in the immediate post-arrest period. Echocardiographic assessment shortly after resuscitation has largely focused on left ventricular (LV) function. We aimed to determine whether post-arrest right ventricular (RV) dysfunction predicts worse survival and poor neurologic outcome in cardiac arrest patients, independent of LV dysfunction.
METHODS: A single-center, retrospective cohort study at a tertiary care university hospital participating in the Penn Alliance for Therapeutic Hypothermia (PATH) Registry between 2000 and 2012.
PATIENTS: 291 in- and out-of-hospital adult cardiac arrest patients at the University of Pennsylvania who had return of spontaneous circulation (ROSC) and post-arrest echocardiograms.
MEASUREMENTS AND MAIN RESULTS: Of the 291 patients, 57% were male, with a mean age of 59 ± 16 years. 179 (63%) patients had LV dysfunction, 173 (59%) had RV dysfunction, and 124 (44%) had biventricular dysfunction on the initial post-arrest echocardiogram. Independent of LV function, RV dysfunction was predictive of worse survival (mild or moderate: OR 0.51, CI 0.26-0.99, p
CONCLUSIONS: Echocardiographic findings of post-arrest RV dysfunction were equally prevalent as LV dysfunction. RV dysfunction was significantly predictive of worse outcomes in post-arrest patients after accounting for LV dysfunction. Post-arrest RV dysfunction may be useful for risk stratification and management in this high-mortality population
Compact Resolved Ejecta in the Nearest Tidal Disruption Event
Tidal disruption events (TDEs) occur when a star or sub-stellar object passes
close enough to a galaxy's supermassive black hole to be disrupted by tidal
forces. NGC 4845 (d=17 Mpc) was host to a TDE, IGR J12580+0134, detected in
November 2010. Its proximity offers us a unique close-up of the TDE and its
aftermath. We discuss new Very Long Baseline Array (VLBA) and Karl G. Jansky
Very Large Array (JVLA) observations, which show that the radio flux from the
active nucleus created by the TDE has decayed in a manner consistent with
predictions from a jet-circumnuclear medium interaction model. This model
explains the source's broadband spectral evolution, which shows a spectral peak
that has moved from the submm (at the end of 2010) to GHz radio frequencies (in
2011-2013) to <1 GHz in 2015. The milliarcsecond-scale core is circularly
polarized at 1.5 GHz but not at 5 GHz, consistent with the model. The VLBA
images show a complex structure at 1.5 GHz that includes an east west extension
~40 milliarcsec (3 pc) long as well as a resolved component 52 milliarcsec (4.1
pc) northwest of the flat-spectrum core, which is all that can be seen at 5
GHz. If ejected in 2010, the NW component must have had v=0.96 c over five
years. However, this is unlikely, as our model suggests strong deceleration to
speeds < 0.5c within months and a much smaller, sub-parsec size. In this
interpretation, the northwest component could have either a non-nuclear origin
or be from an earlier event.Comment: 12 pages, 8 figures, ApJ, in press; v2 includes error corrections and
slight additions to the analysi
Incorporating alternative interaction modes, forbidden links and traitâbased mechanisms increases the minimum trait dimensionality of ecological networks
1. Individual-level traits mediate interaction outcomes and community structure. It is important, therefore, to identify the minimum number of traits that characterise ecological networks, that is, their âminimum dimensionalityâ. Existing methods for estimating minimum dimensionality often lack three features associated with in- creased trait numbers: alternative interaction modes (e.g. feeding strategies such as active vs. sit-and-wait feeding), trait-mediated âforbidden linksâ and a mechanistic description of interactions. Omitting these features can underestimate the trait numbers involved, and therefore, minimum dimensionality. We develop a âmini- mum mechanistic dimensionalityâ measure, accounting for these three features.2. The only input our method requires is the network of interaction outcomes. We assume how traits are mechanistically involved in alternative interaction modes. These unidentified traits are contrasted using pairwise performance inequalities between interacting species. For example, if a predator feeds upon a prey spe- cies via a typical predation mode, in each step of the predation sequence, the predator's performance must be greater than the prey's. We construct a system of inequalities from all observed outcomes, which we attempt to solve with mixed integer linear programming. The number of traits required for a feasible system of inequalities provides our minimum dimensionality estimate.3. We applied our method to 658 published empirical ecological networks includ- ing primary consumption, predatorâprey, parasitism, pollination, seed dispersal and animal dominance networks, to compare with minimum dimensionality estimates when the three focal features are missing. Minimum dimensionality was typically higher when including alternative interaction modes (54% of empirical networks), âforbidden interactionsâ as trait-mediated interaction outcomes (92%) or a mechanistic perspective (81%), compared to estimates missing these features. Additionally, we tested minimum dimensionality estimates on simulated networks with known dimensionality. Our method typically estimated a higher minimum dimensionality, closer to the actual dimensionality, while avoiding the overestimation associated with a previous method.4. Our method can reduce the risk of omitting traits involved in different interaction modes, in failure outcomes or mechanistically. More accurate estimates will allow us to parameterise models of theoretical networks with more realistic structure at the interaction outcome level. Thus, we hope our method can improve predictions of community structure and structure-dependent dynamics
The added value of longitudinal black-blood cardiovascular magnetic resonance angiography in the cross sectional identification of carotid atherosclerotic ulceration
<p>Abstract</p> <p>Background</p> <p>Carotid atherosclerotic ulceration is a significant source of stroke. This study evaluates the efficacy of adding longitudinal black-blood (BB) cardiovascular magnetic resonance (CMR) angiography to cross-sectional CMR images in the identification of carotid atherosclerotic ulceration.</p> <p>Methods</p> <p>Thirty-two subjects (30 males and two females with ages between 48 and 83 years) scheduled for carotid endarterectomy were imaged on a 1.5T GE Signa scanner using multisequence [3D time-of-flight, T1, proton density, T2, contrast enhanced T1], cross-sectional CMR images and longitudinal BB CMR angiography (0.625 Ă 0.625 mm/pixel). Two rounds of review (round 1: cross-sectional CMR images alone and round 2: cross-sectional CMR images plus longitudinal BB CMR angiography) were conducted for the presence and volume measurements of ulceration. Ulceration was defined as a distinct depression into the plaque containing blood flow signal on cross-sectional CMR and longitudinal BB CMR angiography.</p> <p>Results</p> <p>Of the 32 plaques examined by histology, 17 contained 21 ulcers. Using the longitudinal BB CMR angiography sequence in addition to the cross-sectional CMR images in round 2, the sensitivity improved to 80% for ulcers of at least 6 mm<sup>3 </sup>in volume by histology and 52.4% for all ulcers, compared to 30% and 23.8% in round 1, respectively. There was a slight decline in specificity from 88.2% to 82.3%, though both the positive and negative predictive values increased modestly from 71.4% to 78.6% and from 48.4% to 58.3%, respectively.</p> <p>Conclusion</p> <p>The addition of longitudinal BB CMR angiography to multisequence cross-sectional CMR images increases accuracy in the identification of carotid atherosclerotic ulceration.</p
Parton Distributions for Event Generators
In this paper, conventional Global QCD analysis is generalized to produce
parton distributions optimized for use with event generators at the LHC. This
optimization is accomplished by combining the constraints due to existing
hard-scattering experimental data with those from anticipated cross sections
for key representative SM processes at LHC (by the best available theory) as
joint input to the global analyses. The PDFs obtained in these new type of
global analyses using matrix elements calculated in any given order will be
best suited to work with event generators of that order, for predictions at the
LHC. This is most useful for LO event generators at present. Results obtained
from a few candidate PDF sets (labeled as CT09MCS, CT09MC1 and CT09MC2) for LO
event generators produced in this way are compared with those from other
approaches.Comment: 35 pages, 19 figures, and 4 table
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