628 research outputs found
Dectin-1 binding to annexins on apoptotic cells induces peripheral immune tolerance via NADPH oxidase-2
Summary Uptake of apoptotic cells (ACs) by dendritic cells (DCs) and induction of a tolerogenic DC phenotype is an important mechanism for establishing peripheral tolerance to self-antigens. The receptors involved and underlying signaling pathways are not fully understood. Here, we identify Dectin-1 as a crucial tolerogenic receptor binding with nanomolar affinity to the core domain of several annexins (annexin A1, A5, and A13) exposed on ACs. Annexins bind to Dectin-1 on a site distinct from the interaction site of pathogen-derived β-glucans. Subsequent tolerogenic signaling induces selective phosphorylation of spleen tyrosine kinase (SYK), causing activation of NADPH oxidase-2 and moderate production of reactive oxygen species. Thus, mice deficient for Dectin-1 develop autoimmune pathologies (autoantibodies and splenomegaly) and generate stronger immune responses (cytotoxic T cells) against ACs. Our data describe an important immunological checkpoint system and provide a link between immunosuppressive signals of ACs and maintenance of peripheral immune tolerance
Bmi1 loss produces an increase in astroglial cells and a decrease in neural stem cell population and proliferation
The polycomb transcriptional repressor Bmi1 promotes cell cycle progression, controls cell senescence, and is implicated in brain development. Loss of Bmi1 leads to a decreased brain size and causes progressive ataxia and epilepsy. Recently, Bmi1 was shown to control neural stem cell (NSC) renewal. However, the effect of Bmi1 loss on neural cell fate in vivo and the question whether the action of Bmi1 was intrinsic to the NSCs remained to be investigated. Here, we show that Bmi1 is expressed in the germinal zone in vivo and in NSCs as well as in progenitors proliferating in vitro, but not in differentiated cells. Loss of Bmi1 led to a decrease in proliferation in zones known to contain progenitors: the newborn cortex and the newborn and adult subventricular zone. This decrease was accentuated in vitro, where we observed a drastic reduction in NSC proliferation and renewal because of NSC-intrinsic effects of Bmi1 as shown by the means of RNA interference. Bmi1(-/-) mice also presented more astrocytes at birth, and a generalized gliosis at postnatal day 30. At both stages, colocalization of bromodeoxyuridine and GFAP demonstrated that Bmi1 loss did not prevent astrocyte precursor proliferation. Supporting these observations, Bmi1(-/-) neurospheres generate preferentially astrocytes probably attributable to a different responsiveness to environmental factors. Bmi1 is therefore necessary for NSC renewal in a cell-intrinsic mode, whereas the altered cell pattern of the Bmi1(-/-) brain shows that in vivo astrocyte precursors can proliferate in the absence of Bmi1
The gas temperature in flaring disks around pre-main sequence stars
A model is presented which calculates the gas temperature and chemistry in
the surface layers of flaring circumstellar disks using a code developed for
photon-dominated regions. Special attention is given to the influence of dust
settling. It is found that the gas temperature exceeds the dust temperature by
up to several hundreds of Kelvins in the part of the disk that is optically
thin to ultraviolet radiation, indicating that the common assumption that
Tgas=Tdust is not valid throughout the disk. In the optically thick part, gas
and dust are strongly coupled and the gas temperature equals the dust
temperature. Dust settling has little effect on the chemistry in the disk, but
increases the amount of hot gas deeper in the disk. The effects of the higher
gas temperature on several emission lines arising in the surface layer are
examined. The higher gas temperatures increase the intensities of molecular and
fine-structure lines by up to an order of magnitude, and can also have an
important effect on the line shapes.Comment: 14 pages, 10 figures, accepted for publication in A&
Continuum and line modeling of disks around young stars II. Line diagnostics for GASPS from the DENT grid
Aims. We want to understand the chemistry and physics of disks on the basis
of a large unbiased and statistically relevant grid of disk models. One of the
main goals is to explore the diagnostic power of various gas emission lines and
line ratios for deriving main disk parameters such as the gas mass. Methods. We
explore the results of the DENT grid (Disk Evolution with Neat Theory) that
consists of 300 000 disk models with 11 free parameters. Through a statistical
analysis, we search for correlations and trends in an effort to find tools for
disk diagnostic. Results. All calculated quantities like species masses,
temperatures, continuum and line fluxes differ by several orders of magnitude
across the entire parameter space. The broad distribution of these quantities
as a function of input parameters shows the limitation of using a prototype T
Tauri or Herbig Ae/Be disk model. The statistical analysis of the DENT grid
shows that CO gas is rarely the dominant carbon reservoir in disks. Models with
large inner radii (10 times the dust condensation radius) and/or shallow
surface density gradients lack massive gas phase water reservoirs. Also, 60% of
the disks have gas temperatures averaged over the oxygen mass in the range
between 15 and 70 K; the average gas temperatures for CO and O differ by less
than a factor two. Studying the observational diagnostics, the [CII] 158 \mum
fine structure line flux is very sensitive to the stellar UV flux and presence
of a UV excess and it traces the outer disk radius (Rout). In the submm, the CO
low J rotational lines also trace Rout. Low [OI] 63/145 line ratios (< a few)
can be explained with cool atomic O gas in the uppermost surface layers leading
to self-absorption in the 63 \mum line; this occurs mostly for massive
non-flaring, settled disk models without UV excess. ... abbreviatedComment: 15 pages, 25 figures, accepted for publication in A&
Radiation thermo-chemical models of protoplanetary disks II. Line diagnostics
Methods. We use the recently developed disk code ProDiMo to calculate the
physico-chemical structure of protoplanetary disks and apply the Monte-Carlo
line radiative transfer code RATRAN to predict observable line profiles and
fluxes. We consider a series of Herbig Ae type disk models ranging from 10^-6
M_Sun to 2.2 10^-2 M_Sun (between 0.5 and 700 AU) to discuss the dependency of
the line fluxes and ratios on disk mass for otherwise fixed disk parameters.
Results. We find the [CII] 157.7 mum line to originate in LTE from the surface
layers of the disk, where Tg > Td . The total emission is dominated by surface
area and hence depends strongly on disk outer radius. The [OI] lines can be
very bright (> 10^-16 W/m^2) and form in slightly deeper and closer regions
under non-LTE conditions. The high-excitation [OI] 145.5 mum line, which has a
larger critical density, decreases more rapidly with disk mass than the 63.2
mum line. Therefore, the [OI] 63.2 mum/145.5 mum ratio is a promising disk mass
indicator, especially as it is independent of disk outer radius for Rout > 200
AU. CO is abundant only in deeper layers A_V >~ 0.05. For too low disk masses
(M_disk <~10^-4 M_Sun) the dust starts to become transparent, and CO is almost
completely photo-dissociated. For masses larger than that the lines are an
excellent independent tracer of disk outer radius and can break the outer
radius degeneracy in the [OI] 63.2 mum/[CII]157.7 mum line ratio. Conclusions.
The far-IR fine-structure lines of [CII] and [OI] observable with Herschel
provide a promising tool to measure the disk gas mass, although they are mainly
generated in the atomic surface layers. In spatially unresolved observations,
none of these lines carry much information about the inner, possibly hot
regions < 30 AU.Comment: accepted for publication in A&
An atomic and molecular database for analysis of submillimetre line observations
Atomic and molecular data for the transitions of a number of astrophysically
interesting species are summarized, including energy levels, statistical
weights, Einstein A-coefficients and collisional rate coefficients. Available
collisional data from quantum chemical calculations and experiments are
extrapolated to higher energies. These data, which are made publically
available through the WWW at http://www.strw.leidenuniv.nl/~moldata, are
essential input for non-LTE line radiative transfer programs. An online version
of a computer program for performing statistical equilibrium calculations is
also made available as part of the database. Comparisons of calculated emission
lines using different sets of collisional rate coefficients are presented. This
database should form an important tool in analyzing observations from current
and future (sub)millimetre and infrared telescopes.Comment: Accepted for publication in A&A, 14 pages, 5 figure
Marine and freshwater micropearls: biomineralization producing strontium-rich amorphous calcium carbonate inclusions is widespread in the genus <i>Tetraselmis</i> (Chlorophyta)
Unicellular algae play important roles in the biogeochemical cycles of
numerous elements, particularly through the biomineralization capacity of
certain species (e.g., coccolithophores greatly contributing to the organic
carbon pump of the oceans), and unidentified actors of these cycles are
still being discovered. This is the case of the unicellular alga
Tetraselmis cordiformis (Chlorophyta) that was recently discovered
to form intracellular mineral inclusions, called micropearls, which had been
previously overlooked. These intracellular inclusions of hydrated amorphous
calcium carbonates (ACCs) were first described in Lake Geneva (Switzerland)
and are the result of a novel biomineralization process. The genus
Tetraselmis includes more than 30 species that have been widely
studied since the description of the type species in 1878.The present study shows that many other Tetraselmis species share
this biomineralization capacity: 10 species out of the 12 tested contained
micropearls, including T. chui, T. convolutae,
T. levis, T. subcordiformis, T. suecica and
T. tetrathele. Our results indicate that micropearls are not
randomly distributed inside the Tetraselmis cells but are located
preferentially under the plasma membrane and seem to form a definite pattern,
which differs among species. In Tetraselmis cells, the
biomineralization process seems to systematically start with a rod-shaped
nucleus and results in an enrichment of the micropearls in Sr over Ca (the
Sr∕Ca ratio is more than 200 times higher in the micropearls than in
the surrounding water or growth medium). This concentrating capacity varies
among species and may be of interest for possible bioremediation techniques
regarding radioactive 90Sr water pollution.The Tetraselmis species forming micropearls live in various habitats, indicating that
this novel biomineralization process takes place in different environments
(marine, brackish and freshwater) and is therefore a widespread phenomenon.</p
First light of the VLT planet finder SPHERE. I. Detection and characterization of the sub-stellar companion GJ 758 B
GJ758 B is a brown dwarf companion to a nearby (15.76 pc) solar-type,
metal-rich (M/H = +0.2 dex) main-sequence star (G9V) that was discovered with
Subaru/HiCIAO in 2009. From previous studies, it has drawn attention as being
the coldest (~600K) companion ever directly imaged around a neighboring star.
We present new high-contrast data obtained during the commissioning of the
SPHERE instrument at the VLT. The data was obtained in Y-, J-, H-, and Ks-bands
with the dual-band imaging (DBI) mode of IRDIS, providing a broad coverage of
the full near-infrared (near-IR) range at higher contrast and better spectral
sampling than previously reported. In this new set of high-quality data, we
report the re-detection of the companion, as well as the first detection of a
new candidate closer-in to the star. We use the new 8 photometric points for an
extended comparison of GJ758 B with empirical objects and 4 families of
atmospheric models. From comparison to empirical object, we estimate a T8
spectral type, but none of the comparison object can accurately represent the
observed near-IR fluxes of GJ758 B. From comparison to atmospheric models, we
attribute a Teff = 600K 100K, but we find that no atmospheric model can
adequately fit all the fluxes of GJ758 B. The photometry of the new candidate
companion is broadly consistent with L-type objects, but a second epoch with
improved photometry is necessary to clarify its status. The new astrometry of
GJ758 B shows a significant proper motion since the last epoch. We use this
result to improve the determination of the orbital characteristics using two
fitting approaches, Least-Square Monte Carlo and Markov Chain Monte Carlo.
Finally, we analyze the sensitivity of our data to additional closer-in
companions and reject the possibility of other massive brown dwarf companions
down to 4-5 AU. [abridged]Comment: 20 pages, 15 figures. Accepted for publication in A&
Background Light in Potential Sites for the ANTARES Undersea Neutrino Telescope
The ANTARES collaboration has performed a series of {\em in situ}
measurements to study the background light for a planned undersea neutrino
telescope. Such background can be caused by K decays or by biological
activity. We report on measurements at two sites in the Mediterranean Sea at
depths of 2400~m and 2700~m, respectively. Three photomultiplier tubes were
used to measure single counting rates and coincidence rates for pairs of tubes
at various distances. The background rate is seen to consist of three
components: a constant rate due to K decays, a continuum rate that
varies on a time scale of several hours simultaneously over distances up to at
least 40~m, and random bursts a few seconds long that are only correlated in
time over distances of the order of a meter. A trigger requiring coincidences
between nearby photomultiplier tubes should reduce the trigger rate for a
neutrino telescope to a manageable level with only a small loss in efficiency.Comment: 18 pages, 8 figures, accepted for publication in Astroparticle
Physic
First light of the VLT planet finder SPHERE. II. The physical properties and the architecture of the young systems PZ Tel and HD 1160 revisited
[Abridged] Context. The young systems PZ Tel and HD 1160, hosting known
low-mass companions, were observed during the commissioning of the new planet
finder SPHERE with several imaging and spectroscopic modes. Aims. We aim to
refine the physical properties and architecture of both systems. Methods. We
use SPHERE commissioning data and REM observations, as well as literature and
unpublished data from VLT/SINFONI, VLT/NaCo, Gemini/NICI, and Keck/NIRC2.
Results. We derive new photometry and confirm the nearly daily photometric
variability of PZ Tel A. Using literature data spanning 38 yr, we show that the
star also exhibits a long-term variability trend. The 0.63-3.8 mic SED of PZ
Tel B allows us to revise its properties: spectral type M7+/-1, Teff=2700+/-100
K, log(g)<4.5 dex, log(L/L_Sun)=-2.51+/-0.10 dex, and mass 38-72 MJ. The 1-3.8
mic SED of HD 1160 B suggests a massive brown dwarf or a low-mass star with
spectral type M5.5-7.0, Teff=3000+/-100 K, [M/H]=-0.5-0.0 dex,
log(L/L_Sun)=-2.81+/-0.10 dex, and mass 39-168 MJ. We confirm the deceleration
and high eccentricity (e>0.66) of PZ Tel B. For e<0.9, the inclination,
longitude of the ascending node, and time of periastron passage are well
constrained. The system is seen close to an edge-on geometry. We reject other
brown dwarf candidates outside 0.25" for both systems, and massive giant
planets (>4 MJ) outside 0.5" for the PZ Tel system. We also show that K1-K2
color can be used with YJH low-resolution spectra to identify young L-type
companions, provided high photometric accuracy (<0.05 mag) is achieved.
Conclusions. SPHERE opens new horizons in the study of young brown dwarfs and
giant exoplanets thanks to high-contrast imaging capabilities at optical and
near-infrared wavelengths, as well as high signal-to-noise spectroscopy in the
near-infrared from low (R~30-50) to medium resolutions (R~350).Comment: 25 pages, 23 figures, accepted for publication in A&A on Oct. 13th,
2015; version including language editing. Typo on co-author name on astroph
page corrected, manuscript unchange
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