923 research outputs found
Inhibiting CDK4/6 in pancreatic ductal adenocarcinoma via microRNA-21
Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive malignancies, with a 5-year survival rate of 5–10 %. The high mortality rate is due to the asymptomatic progression of clinical features in metastatic stages of the disease, which renders standard therapeutic options futile. PDAC is characterised by alterations in several genes that drive carcinogenesis and limit therapeutic response. The two most common genetic aberrations in PDAC are the mutational activation of KRAS and loss of the tumour suppressor CDK inhibitor 2A (CDKN2A), which culminate the activation of the cyclin-dependent kinase 4 and 6 (CDK4/6), that promote G1 cell cycle progression. Therapeutic strategies focusing on the CDK4/6 inhibitors such as palbociclib (PD-0332991) may potentially improve outcomes in this malignancy. MicroRNAs (miRs/miRNAs) are small endogenous non-coding RNA molecules associated with cellular proliferation, invasion, apoptosis, and cell cycle. Primarily, miR-21 promotes cell proliferation and a higher proportion of PDAC cells in the S phase, while knockdown of miR-21 has been linked to cell cycle arrest at the G2/M phase and inhibition of cell proliferation. In this study, using a CRISPR/Cas9 loss-of-function screen, we individually silenced the expression of miR-21 in two PDAC cell lines and in combination with PD-0332991 treatment, we examined the synergetic mechanisms of CDK4/6 inhibitors and miR-21 knockouts (KOs) on cell survival and death. This combination reduced cell proliferation, cell viability, increased apoptosis and G1 arrest in vitro. We further analysed the mitochondrial respiration and glycolysis of PDAC cells; then assessed the protein content of these cells and revealed numerous Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways associated with PD-0332991 treatment and miR-21 knocking out. Our results demonstrate that combined targeting of CDK4/6 and silencing of miR-21 represents a novel therapeutic strategy in PDAC
A rich, nearby galaxy cluster in Sagittarius
We report on the existence of a rich, heavily obscured galaxy cluster (or a set of clusters) in Sagittarius, centered near l_(II) ≃ 359°, b_(II) ≃ 8°. About 30 objects, originally identified by Terzan and his collaborators, were imaged and followed up spectroscopically. We present here redshifts for 21 galaxies found among them. There is a pronounced concentration at cz ≃ 8600 km/s (containing 14 out of the 21 galaxies), and another possible concentration near cz ≃ 11 340 km/s (five out of 21). This putative Sagittarius cluster is probably part of a larger system, involving the Ophiuchus cluster at l_(II) ≃ 1°, b_(II) ≃ 9°, cz ≃ 8400 km/s, previously identified by Johnston et al. and Wakamatsu and Malkan. The heavy extinction on this line of sight (we estimate A_v ~ 5^m from the observed Balmer decrements) suggests that there is a much larger, as yet undetected number of galaxies in this direction. We propose that the Sagittarius-Ophiuchus concentration may be a massive cluster, or even a supercluster, comparable in richness to the Coma-A 1367 system, and at a comparable distance. The existence of this concentration serves as a reminder that some possibly dynamically important constituents of the local large-scale structure may be absent from the galaxy .catalogs available now, and the dynamical analyses based on them
Cosmological Model Predictions for Weak Lensing: Linear and Nonlinear Regimes
Weak lensing by large scale structure induces correlated ellipticities in the
images of distant galaxies. The two-point correlation is determined by the
matter power spectrum along the line of sight. We use the fully nonlinear
evolution of the power spectrum to compute the predicted ellipticity
correlation. We present results for different measures of the second moment for
angular scales \theta \simeq 1'-3 degrees and for alternative normalizations of
the power spectrum, in order to explore the best strategy for constraining the
cosmological parameters. Normalizing to observed cluster abundance the rms
amplitude of ellipticity within a 15' radius is \simeq 0.01 z_s^{0.6}, almost
independent of the cosmological model, with z_s being the median redshift of
background galaxies.
Nonlinear effects in the evolution of the power spectrum significantly
enhance the ellipticity for \theta < 10' -- on 1' the rms ellipticity is \simeq
0.05, which is nearly twice the linear prediction. This enhancement means that
the signal to noise for the ellipticity is only weakly increasing with angle
for 2'< \theta < 2 degrees, unlike the expectation from linear theory that it
is strongly peaked on degree scales. The scaling with cosmological parameters
also changes due to nonlinear effects. By measuring the correlations on small
(nonlinear) and large (linear) angular scales, different cosmological
parameters can be independently constrained to obtain a model independent
estimate of both power spectrum amplitude and matter density \Omega_m.
Nonlinear effects also modify the probability distribution of the ellipticity.
Using second order perturbation theory we find that over most of the range of
interest there are significant deviations from a normal distribution.Comment: 38 pages, 11 figures included. Extended discussion of observational
prospects, matches accepted version to appear in Ap
The Extragalactic Distance Scale Key Project XXVII. A Derivation of the Hubble Constant Using the Fundamental Plane and Dn-Sigma Relations in Leo I, Virgo, and Fornax
Using published photometry and spectroscopy, we construct the fundamental
plane and D_n-Sigma relations in Leo I, Virgo and Fornax. The published Cepheid
P-L relations to spirals in these clusters fixes the relation between angular
size and metric distance for both the fundamental plane and D_n-Sigma
relations. Using the locally calibrated fundamental plane, we infer distances
to a sample of clusters with a mean redshift of cz \approx 6000 \kms, and
derive a value of H_0=78+- 5+- 9 km/s/Mpc (random, systematic) for the local
expansion rate. This value includes a correction for depth effects in the
Cepheid distances to the nearby clusters, which decreased the deduced value of
the expansion rate by 5% +- 5%. If one further adopts the metallicity
correction to the Cepheid PL relation, as derived by the Key Project, the value
of the Hubble constant would decrease by a further 6%+- 4%. These two sources
of systematic error, when combined with a +- 6% error due to the uncertainty in
the distance to the Large Magellanic Cloud, a +- 4% error due to uncertainties
in the WFPC2 calibration, and several small sources of uncertainty in the
fundamental plane analysis, combine to yield a total systematic uncertainty of
+- 11%. We find that the values obtained using either the CMB, or a flow-field
model, for the reference frame of the distant clusters, agree to within 1%. The
Dn-Sigma relation also produces similar results, as expected from the
correlated nature of the two scaling relations. A complete discussion of the
sources of random and systematic error in this determination of the Hubble
constant is also given, in order to facilitate comparison with the other
secondary indicators being used by the Key Project.Comment: 21 pages, 3 figures, Accepted for publication in Ap
The disruption of nearby galaxies by the Milky Way
Interactions between galaxies are common and are an important factor in
determining their physical properties such as position along the Hubble
sequence and star-formation rate. There are many possible galaxy interaction
mechanisms, including merging, ram-pressure stripping, gas compression,
gravitational interaction and cluster tides. The relative importance of these
mechanisms is often not clear, as their strength depends on poorly known
parameters such as the density, extent and nature of the massive dark halos
that surround galaxies. A nearby example of a galaxy interaction where the
mechanism is controversial is that between our own Galaxy and two of its
neighbours -- the Large and Small Magellanic Clouds. Here we present the first
results of a new HI survey which provides a spectacular view of this
interaction. In addition to the previously known Magellanic Stream, which
trails 100 degrees behind the Clouds, the new data reveal a counter-stream
which lies in the opposite direction and leads the motion of the Clouds. This
result supports the gravitational model in which leading and trailing streams
are tidally torn from the body of the Magellanic Clouds.Comment: 17 pages with 5 figures in gif format, scheduled for publication in
the August 20th, 1998 issue of Natur
Optical and Radio Observations of the Afterglow from GRB990510: Evidence for a Jet
We present multi-color optical and two-frequency radio observations of the
bright SAX event, GRB 990510. The well-sampled optical decay, together with the
radio observations are inconsistent with simple spherical afterglow models. The
achromatic optical steepening and the decay of the radio afterglow both
occuring at day are evidence for hydrodynamical evolution of the
source, and can be most easily interpreted by models where the GRB ejecta are
collimated in a jet. Employing a simple jet model to interpret the
observations, we derive a jet opening angle of , reducing the
isotropic gamma-ray emission of erg by a factor . If the jet interpretation is correct, we conclude that GRB observations
to-date are consistent with an energy for the central source of E \lsim
10^{52} erg.Comment: 12 pages, 2 figures. Version accepted for publication in ApJ Letter
The Protean Challenge of Game Collections at Academic Libraries
The rise of game development and game studies on university campuses prompts academic libraries to consider how to support teaching and research in this area. This article examines current issues and challenges in the development of game collections at academic libraries. The gaming ecosystem has become more complex and libraries may need to move beyond collections largely based on console video games. This article will advance the discussion by considering emerging issues to support access to the full range of games. The article will use examples from Carleton University Library, Ottawa, which has been developing a game collection since 2008
Ray Tracing Simulations of Weak Lensing by Large-Scale Structure
We investigate weak lensing by large-scale structure using ray tracing
through N-body simulations. Photon trajectories are followed through high
resolution simulations of structure formation to make simulated maps of shear
and convergence on the sky. Tests with varying numerical parameters are used to
calibrate the accuracy of computed lensing statistics on angular scales from
about 1 arcminute to a few degrees. Various aspects of the weak lensing
approximation are also tested. For fields a few degrees on a side the shear
power spectrum is almost entirely in the nonlinear regime and agrees well with
nonlinear analytical predictions. Sampling fluctuations in power spectrum
estimates are investigated by comparing several ray tracing realizations of a
given model. For survey areas smaller than a degree on a side the main source
of scatter is nonlinear coupling to modes larger than the survey. We develop a
method which uses this effect to estimate the mass density parameter Omega from
the scatter in power spectrum estimates for subregions of a larger survey. We
show that the power spectrum can be measured accurately from realistically
noisy data on scales corresponding to 1-10 Mpc/h. Non-Gaussian features in the
one point distribution function of the weak lensing convergence (reconstructed
from the shear) are also sensitive to Omega. We suggest several techniques for
estimating Omega in the presence of noise and compare their statistical power,
robustness and simplicity. With realistic noise Omega can be determined to
within 0.1-0.2 from a deep survey of several square degrees.Comment: 59 pages, 22 figures included. Matches version accepted for Ap
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